in greenhouses€¦ · jojanneke rodenburg harry stijger pieternel van velden editor helen...

In GreenhousesThe international magazine for greenhouse growers

Number 4

October 2015

Volume 4

Focused fertilisation requiresknowledge, insight and experience

Page 34 Production very closelylinked to amount of intercepted light

Page 23 High quality tomatoesin innovative plasticgreenhouse in Mexico

Page 7 Automatic containerfiller prevents errors during fertilisation

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“Even in the summer it can

take hours before the correct

EC reaches the last point.”

Page 44

3

Feature

Research

Report

5 Introduction chief editor Henk van Esch

15 Local report: Burston Nurseries (UK) breaks with

tradition and grows roses from cuttings

23 Local report: Hydroponic Green Valley Produce: Innovative

plastic greenhouse for high quality tomatoes in Mexico

33 The series of pests and diseases: Phytophthora

48 Local report: Dutch entrepreneur teaches local producers in

Georgia how to produce more effectively

51 Product news

Columns

9 Phalaenopsis distributor Eric Moor

17 Tomato grower Frank van Kleef

12 DNA is the recipe book for all the processes in the plant

30 When choosing a glass type also consider the cleaning of it

34 Production very closely linked to amount of intercepted light

42 ‘Avoid delay when distributing fertilisers and crop protection agents’

46 What the slab says is not

automatically the opinion of the plant

10 Alternative to iron chelates tests positive in practise

18 Market ready for affordable roof with high level of insulation and light transmission

26 Extra light and save energy in ideal winter-light greenhouse

39 News from Wageningen UR Greenhouse Horticulture

40 Short term non-chemical approach to Tuta absoluta and thrips

7 Automatic container filler prevents errors during fertilisation

20 Innovative fertilisation concept for chrysanthemums also looks at soil condition

28 Ethylene gives better control over the ripening of tomatoes

36 No lighting, but still two energy screens without dehumidification

44 Creative device is extra tool in fight against adult thrips

Coverphoto

Dutch strawberry nursery, Van Gennip Kwekerijen, chose a fully automatic fertiliser container filler. (page 7) Against higher costs there are big benefits: convenience, prevention of errors and saving on expensive management time. (Photo: Wilma Slegers)

Further

NUMBER 4OCTOBER 2015

Content

IN GREENHOUSES NO 4 OCTOBER 2015

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5IN GREENHOUSES NO 4 OCTOBER 2015

Colophon

Contributors

Contributors to this issue Marleen Arkesteijn Helen ArmstrongJos BezemerAnita ElingsEp HeuvelinkKarin van HoogstratenTijs Kierkels Frank van KleefEric MoorJojanneke RodenburgHarry StijgerPieternel van Velden

EditorHelen Armstrong

Design Van de Sande, NootdorpTheo van Vliet

Contact

Advertising sales Holland and BelgiumWouter van EschTelephone: +31 6 - 16 47 69 98E-mail: [email protected]

International advertising sales Horti Media SalesMiguel Mendes de LeónTelephone: +31 6 - 81 54 33 66E-mail: [email protected]

Editorial In Greenhouses is published byHorti-Text BV Bastion Willem 183445 DH WoerdenThe Netherlands

Henk van Esch Telephone: +31 6 - 47 98 25 85E-mail: [email protected]

Internet

Website & Twitterwww.ingreenhouses.comtwitter.com/ingreenhouses

Digital archiveAll editions are digitally available on our site.

Subscriptions and change of addressTo request or terminate a subscription or inform us of a change of address simply go to www.ingreenhouses.com and click on the heading Readers.

Or by post: In GreenhousesPostbus 262630 AA NootdorpThe Netherlands.

Introduction

Fertilisation is a tricky subject, whether the crop is in soil or in a substrate. It’s because many

factors play a role in fertilisation. Compare it, for example, with temperature. For this you only

need a thermometer, linked or not to a climate computer, that precisely displays the situation.

With fertilisation it’s not only the various elements that play a role, but also the relationship

between the elements, the concentration of the elements and thus the amount of water that

a grower supplies. It becomes even more difficult when you include the uptake by the crop

as well.

Many growers base the fertilisation on a crop recipe. But Dutch research shows that

this is not always accurate: the plants don’t always get what they need. This is because the

measurements taken in the slab may not show the actual requirement of the plants. This

has led to the design of a new method (page 46). By using a model, a nursery can determine

the actual uptake by the plant. In this way a grower can provide

fertilisers in a much more focused way.

Nearly all modern greenhouse nurseries utilise a fertilisation unit

which, as standard, uses an A and B container with an automatic pH

control. The preparation and filling of the containers is an exact job;

mistakes are mercilessly punished through loss of yield and quality.

For this reason more growers are switching to automatic container

fillers (page 7). This requires an investment but they do save money

too and more importantly they prevent mistakes.

Good fertilisation requires knowledge about the chemical elements but you also need

to know the effect of each individual element. The role of the most important nutrients

is covered in the book, Plant Physiology In Greenhouses, which can be ordered via our

website www.ingreenhouses.com/books. With this information a grower can further develop

his knowledge and understanding and thereby further optimise production in terms of both

quantity and quality.

PS. Next issue of In Greenhouses will be published January 2016 just before IPM Essen.

Focused fertilisation requires knowledge, insight and experience

HENK VAN ESCHCHIEF EDITOR

“Good fertilisation requires

insight into the chemical elements

and their individual effect.”

The contents of In Greenhouses has been compiled as carefully as possible and to the best of the publisher’s and authors’ knowledge. However, the publisher and authors cannot in any way guarantee the accuracy or completeness of the information and they accept no liability for damage, of any nature whatsoever, resulting from acts and/or decisions based on the information included in this journal. No part of this publication may be reproduced, stored or made public without prior written consent from the publisher and authors.

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IN GREENHOUSES NO 4 OCTOBER 2015 7

Strawberry grower Theo van Gennip: “One error during fertilisation can be very costly.”

Nurseries that are starting to invest again are choosing remarkably often for fully automatic fertiliser container fillers. Dutch strawberry nursery Van Gennip Kwekerijen already has four and a fifth is in the pipeline. Theo van Gennip is very pleased with his choice: “It is always accurate, you don’t have to drag heavy bags and you save on expen-sive man-hours.”

Even a large horticultural company usually

has a very flat organisational structure: One

director, one manager, several people with

a certain specialism and many unskilled

labourers. That means that work that requires

great accuracy, automatically ends up being

done by the owner or manager. And their

time is expensive.

“In the past it used to cost me one and

half hours every three days just filling the

fertiliser containers. I used to use a litre

counter, which you had to rinse and reset

every time you switched to a different

fertiliser ingredient. You really have to pay

attention because one mistake can cost a lot

of money. And at such a moment the tele-

phone goes, of course. Then you’re no longer

certain where you were! Since we started

using automatic liquid fertiliser container

fillers we have had far fewer worries,” says

Theo van Gennip.

Many advantages Together with his three brothers and another

grower, Theo owns Mts. Van Gennip Kweke-

rijen that has five locations in the southeast

of the Netherlands. They grow strawberries

under glass, in gutters and in soil and they

Text: Tijs KierkelsImages: Wilma Slegers

STRAWBERRIESREPORT

No more topping up nutrient containers in the weekend

Automatic container filler prevents errors during fertilisation

Continued on page 8 >

7-9-Thema12-OG-Reportage-basis1-3pag.indd 2 28-09-15 09:02


Extra shotThe grower can set dozens of different

fertilisation recipes. In principle, Van Gennip

uses two for the strawberries: a start strategy

and a potassium strategy for when the plants

start to flower. He has a different recipe for

the mother plants. He formulated them

together with the representative and these

change just slightly throughout the year.

He takes leaf and soil samples each week

and makes adjustments based on the results.

“We can give an additional ‘shot’ of fertiliser

from the C-container if necessary. We do use

solid fertilisers for this,” he says. Everything is

recirculated after it’s been disinfected. On an

annual basis this saves 25% on fertilisers

compared with non-recirculation.

GravityThe automatic container filler has its own

software and therefore can “think” for itself

and can be operated stand alone, but a link to

The fully automatic container filler individually collects the liquid fertilisers from one of the

large storage tanks using the pipework.

René van der Stam at the control panel:

“All the data is kept up-to-date.”

propagate their own plants. The latest nursery

in Someren is a greenhouse of 6.1 ha, that was

built in 2013, plus field trays. “We start the

season here with 2.65 ha of a lit Sonata crop

which we harvest from mid February to mid

April. The cuttings from the mother plants are

brought into the greenhouse and we follow

this with an early autumn crop of Elsanta.

The other 3.45 ha is unlit; here we have an

autumn and spring crop of Elsanta. Then we

bring the mother plants into the greenhouse

that have already been put onto the field

trays,” he says.

FertiFills from Hortimax are already used

at the other locations and the grower didn’t

consider for one moment doing it any other

way in Someren. It required an extra invest-

ment of some € 25,000 and the liquid ferti-

lisers are more expensive than solid ones but

it brings a lot of advantages, says Van Gennip.

“The benefits are the convenience and the

hours saved. Filling always came at an

inconvenient time. You had to wait until the

container was empty and it’s remarkable that

that often seemed to happen in the weekend!

Also, you no longer make any mistakes; the

machine can do it better than you can do it

yourself. And besides it’s safer. Some of the

materials are really messy: the acids, bases

and the iron chelate. When we built the

greenhouse we didn’t even consider any other

alternative,” he says.

Fully automaticThe fertiliser container filler works in exactly

the same way as a person would do the job

but instead its fully automatic. When the

level sensor in one of the A or B containers

gives a sign it starts to work. One by one and

via the pipework it collects a liquid fertiliser

from one of the large storage tanks and then

fills the A- and B-reactor containers that are

positioned on a platform. When the correct

amount has been reached it rinses the pipe-

work with water and then it’s the turn of the

next fertiliser.

When all the fertiliser ingredients are com-

pleted each reactor container is filled with

water. First one of the 500-litre reactor con-

tainers is filled and then the other. As soon as

this is finished the solution goes from the

machine to the A and B containers. Therefore

you don’t have to wait until the containers

are empty and the substrate unit (FertiMix)

can keep running during the refilling. It also

prepares the acid container. “I never have to

fill the containers unexpectedly, I just have to

occasionally keep an eye on the stocks,” says

the grower. “We still make up the container

for trace elements ourselves; we make up a

batch that will last one and a half months.

Then the automatic container filler automati-

cally mixes in these trace elements.”

Continued > from page 7


Dutch strawberry nursery, Van Gennip

Kwekerijen, choose a fully automatic

fertiliser container filler. Counter-ba-

lancing the extra investment needed

for the equipment and the higher price

of the liquid fertiliser (compared with

solids) are the benefits of convenience,

prevention of errors and saving on

expensive management time.

Column

Globalisation, how do you do that?

In May this year we, Sion Orchids, finally started

transplanting the first plants at our propagation site

in Brazil. We want to become international, but how

do you do that? We started simply by trial and error. I

still can’t explain how to go about it exactly, just share

our experiences.

Eight years ago I joined a Dutch trade mission be-

cause I’d heard that there were orchid growers in Brazil.

The mission coincided with a fair. That was convenient

as it enabled us to speak to many people from the

sector and visit nurseries. It helped that several growers

had already visited our Dutch nursery. I came home

enthusiastic, saw plenty of opportunities and returned

to Brazil very quickly. I visited some more nurseries

and went in search of a local agent. I found one very

quickly. With hindsight, possibly too quickly because

a good agent needs to be transparent and certainly not

count on too high margins.

After eight years and two annual visits to Brazil we

came up with the idea to propagate locally and to

look for a location. I was lucky to find a relatively new

greenhouse that, due to private circumstances, had

been standing empty for a few years. We equipped

the rental greenhouse to our own taste. Establishing

a limited company and arranging the financing cost a

lot of time because despite the TV commercials by the

Dutch banks about Brazil, it appeared that nothing

could be arranged within the country.

For good local management we let someone work

alongside us in our nursery for a year. If the test

phase is successful we also want a Dutchman on site.

The climate computers are linked together and are

monitored daily and remotely from the Netherlands.

Every month someone from Sion goes to South

America to supervise the cultivation and give advice.

We decided to start very carefully. On one hand

because of the financing and, on the other hand, we

first have a lot to learn. Only when we feel that we

have sufficient control will we try to scale up. We

have learnt that you need to adjust to the culture

and that everything takes more time. Also you need

to learn to cope with a temperature of 36°C and

humidity of nearly 100%.

It has given our company a ‘boost’ to take this

international step. Only time will tell if it was the

right step. But if there’s no fight, there’s no victory!

Eric Moor, phalaenopsis supplier, De Lier

[email protected] or twitter at @Eric_moor

Column

9

the computer is more logical. What is unusual

is that it doesn’t contain a pump for pumping

the liquids to the A- and B-containers. “The

machine is positioned higher and gravity does

the work when the machine opens the valves,”

explains René van der Stam of Hortimax. “All

the data is kept up to date: the amount of

fertilisers and litres of water, how often the

machine runs, etc.”

This is an additional point of measurement

for the grower who supplies a plethora of

information to retail customer Albert Heijn,

not only the product characteristics but also

the amount of substances used during pro-

duction. This is compulsory in order to comply

with EurepGap-regulations. Why the customer

needs figures about fertilisation is still a mys-

tery to him.

Purchase price Van der Stam has noticed a striking increase

in interest for automatic fertiliser fillers over

the last few months. He thinks the reason is a

combination of two factors: “Here and there

growers are starting to earn money again so

once again there is room for investment. And

the rising size of nurseries plays a role. Filling

the containers is time consuming and because

it is very precise work it takes a lot of concen-

tration so it is mainly the job for the owner of

nursery manager, who already has many jobs

to do.”

The purchase price and the cost of the

liquid fertilisers are a hurdle. You can cal-

culate what you save on labour, for example

three hours per week on a management

salary. In addition there are qualitative

benefits, such as the prevention of expensive

errors and the relief it brings.

Summary

Van Gennip Kwekerijen starts the season with a lit crop of Sonata.

After the mother plants have been in the

greenhouse there follows an early autumn

crop of Elsanta.




Iron is an essential element that is requi-red for the formation of chlorophyll and in doing so prevents chlorosis. Because the element doesn’t usually remain dis-solved in a solution – and therefore is not available to the plant – for years growers have been using iron chelates. With the launch of a new fertiliser the iron is bound in a different way, namely in combination with polyphosphates. When given via a separate container it appears to work well in practice. The fertiliser also produces other effects such as less leaf curling and it makes UV dis-infection of drain water more efficient. Recent research and practical experiences support these findings.

In 2012 and 2013 Wageningen UR Greenhouse

Horticulture, in the Netherlands, was commis-

sioned to carry out research on the fertiliser

Micronutri Fe by the producer, Prayon. Kurt

Verhelst explains the reason for the research.

“The horticultural sector had been using

organic chelates for decades to ensure that

the plant could take up iron. As a large

phosphate supplier we think that a mineral

fertiliser based on iron polyphosphate has the

same effect. In addition, it prevents problems

during UV disinfection. Of course there is

scepticism, so with proper research we want

to validate its activity.”

During the trials the new fertiliser was

compared with the iron chelate DTPA. Both

products were found to prevent chlorosis

equally well. In addition, the new fertiliser

appeared to have a favourable effect on

calcium transport in the plant, so less leaf

cupping occurred. The fertiliser was launched

on the market at the end of 2013.

Calcium uptakeDutch high wire cucumber grower, Jan Reijm,

of Berkel en Rodenrijs, was one of its first

users. Ewoud van der Ven, crop advisor at

DLV Plant, gave him advice. “Last year I grew

a cucumber variety that was sensitive to leaf

necrosis at the top. That’s why I especially

chose this fertiliser because– in addition to

the prevention of chlorosis – it also seems to

improve calcium uptake,” says Reijm.

Although the crop developed well, he still

questioned its application. “We take weekly

samples of the drain water and we saw the

iron level drop each time. Although the plants

remained lovely and green, we were worried

about that decline. Time and again I gave

more iron polyphosphate. That’s why in the

autumn I switched over to ferric oxide just to

be sure.”

Research carried out againAfter this experience in the nursery, the manu-

facturer decided to ask Wageningen UR Green-

house Horticulture to carry out research

again on this fertiliser and a few other new

ones. Wim Voogt led the research. From Sep-

tember to November 2014 a trial was carried

out on a substrate-based crop of cucumbers

and from January to April 2015 on a tomato

crop to compare the new fertiliser with DTPA

iron chelate. Both trials had the same objec-

tive. Voogt: “The first question for the resear-

chers was whether the iron content remained

stable. And the second question was whether

indeed the fertiliser led to less leaf cupping in

cucumber and less tipburn in tomato, which

could suggest a better calcium transport.”

Dry matter analysisIn order to answer the first question the

water supply and the drain water were inten-

sively sampled in both trials. The results

confirmed what had been seen in practice:

The iron concentration in the drain water

was significantly lower than in the drain

from the plants that had received the iron

chelates. Especially when the pH rose above

6.5, the iron was released much more easily

and disappeared from the solution.

But that does not say everything about the

Text: Karin van HoogstratenImages: Studio G.J. Vlekke

NUTRITIONAL ELEMENTS RESEARCH

Separate administration gives better results

Alternative to iron chelates tests positive in practise

Verhelst: “With proper research we can validate the activity of the fertiliser.”

Van der Ven: “By dosing separately the fertiliser is not crowded out.”

Wim Voogt: “Iron polyphosphate leads to less leaf cupping in cucumber.”

10-11-Thema17_IG-Onderzoek-basis1.indd 1 28-09-15 09:09


availability of iron and the uptake by the

crop, says Voogt. “We noticed that the plant

didn’t suffer. Measuring the iron in the drain

solution is not necessarily a good measure of

the amount of iron available. Therefore we

also carried out a dry matter analysis on the

leaves. This showed that the iron level in the

leaf was virtually the same as in the chelate-

treatments. Therefore, despite the low levels

in the slab and drain, sufficient iron is avai-

lable for the plant. Ultimately the growth and

yield are the best indicators for the activity.

Here we observed no differences between the

trial area that received iron chelate and the

area that received iron polyphosphate.”

Black-whiteClear differences were seen regarding the tip-

burn, indicating a side effect of the fertiliser.

The second question for the researchers was

therefore easy to answer. “We could establish

that very black and white. We saw leaf cupping

all over the area that received DTPA. In the area

that was treated with iron polyphosphate we

didn’t see it at all. That suggests that the cal-

cium transport through the plant is better.

That is consistent with the theory that

polyphosphate can bind calcium,” says the

researcher. In cucumber production tipburn

and leaf cupping are a nuisance; in tomatoes

these can be entry points for Botrytis. In

short, the prevention of curled leaf edges is a

welcome side effect of the fertiliser.

Separate dosingCucumber grower Reijm chose – despite his

initial doubts – to apply the iron polyphos-

phate right from the start of the new crop.

Based on advice from the manufacturer and

his own advisor he now administers the

fertiliser via a separate mixing container and

doesn’t add it to the B-container, like he did

last year. Van der Ven: “By dosing it separately

the fertiliser doesn’t have time to react with

other substances. There is less crowding. It

appears to work. Of course it does require

extra effort and investment by the grower.”

Reijm added that he choose to measure

the values in the slab and not sample the

drain water. This gives him more insight. So

far he has managed to achieve the target

values for iron in the slab, even when the pH

rose above 7. “The crop and the buds are nice

and green, there’s no chlorosis and fewer

cupped leaf than last year. In theory that can

be the result of better calcium uptake due

to the fertiliser but I’m not sure if that’s the

reason. This year I have also used anti-con-

densation film. That too could have a positive

effect.”

Disinfecting capacity higherA clear advantage of using iron polyphos-

phate is the ability to disinfect the drain

water much more easily. The capacity of

his Vialux-disinfection unit has increased

now that he no longer uses chelates. Reijm:

“Chelates cake on and make the water cloudy.

The cleaner the water the faster the UV-

disinfection unit can work. Because we treat

both drain water and rain water equally, in

the summer we have to disinfect 450m3 of

water per day. Faster disinfection is more

economical for us.”

Research Voogt explains that iron poly-

phosphate remains in tact better during

disinfection, also when using chlorine dioxide

or hydrogen peroxide. Traditional iron

products are broken down and precipitate out

which can lead to dirt in the system. So what

did they conclude? Iron polyphosphates are

an interesting alternative but you do need to

use a different user manual.

An alternative fertiliser to iron chelates

appears to work well, although it needs

to be administered via a separate

container. The fertiliser also offers

advantages for UV disinfection. In the

meantime, purer and low-sodium iron

chelates are entering the market, which

allow for longer recycling.

Summary

Strong, green tops and not a trace of chlorosis: Jan Reijm’s high wire cucumbers are not suffering

from an iron deficiency.

Iron chelates are improving, says Boris

Berkhout, of Horticoop. Due to the recy-

cling of water that takes place it is impor-

tant that products become purer. He sug-

gests the first step would be to switch from

3% DTPA to 6% DTPA. “That first contains

sodium, the second is sodium-free.”

The new iron chelate Bolikel XP goes

one step further. It is sodium-free, contains

6% iron and the active chelate HBED is 100%

ortho-ortho. “This means that it contains the

maximum concentration of the active

agent in ferric oxide. If you needed one kilo

of EDDHA-chelate, in this case you can

manage with 600 gram. Also, at a lower

dosage you have less red colouring.”

Iron chelates becoming purer

Boris Berkhout: “Iron chelates are beco-

ming increasingly purer.”

10-11-Thema17_IG-Onderzoek-basis1.indd 2 28-09-15 09:09


DNAFEATURE

12

It’s sometimes called a blueprint: DNA, the carrier of genetic information. But the term recipe book covers it better. It explains how the plant can respond to changing conditions. Plant breeders take advantage of natural variations in DNA. Genetic modification can make their job easier.

DNA is short for deoxyribonucleic acid.

A bizarre name for what can be called the

mystery of life. Only a variation in the

bases in DNA determines the vast diversity

of all living things. There are just four of

these bases: guanine (G), cytosine (C), adenine

(A) and thymine (T). A gene is then charac-

terised by a long series of letters consisting

merely of these four options, for example,

AAGCTTACC and so on.

Long spiral staircase DNA is often presented as a very long spiral

staircase. The banister and railing is made

from a sugar and a phosphate group. The

treads are made up of bases. A base is a mole-

cule with a free electron pair that can be

shared with an acidic molecule. These bases

are always connected in the same way to

each other. A is always opposite T and C is

always opposite G.

In order for an inherited trait to be

expressed, the gene has to be readable. The

bases then let go of each other, allowing the

strands to become free. Then messenger RNA

is formed which copies precisely the codes

on the gene. This message is sent to the

ribosomes where it is read and the protein

is made.

Researchers often say that a gene encodes,

for example, resistance to fungi. But strictly

speaking genes encode only for the produc-

tion of proteins, the plant’s building blocks.

The order of bases in the gene determines

the order in which amino acids bind to each

other and form proteins. This is a remarkably

simple code. The combination of just three

bases, for example AAC, determines which of

the 20 amino acids is next in line. The order

of the amino acids in the protein determines

the way in which the protein is folded. And

the way of folding is crucial to its behaviour.

A small mistake in the transcription can

make it completely ineffective.

The same genetic information All cells have the same genetic information.

For example, the cells in a tomato leaf also

contain all the information needed for flower

and fruit formation. This is easy to appreciate

knowing that complete plants can be produ-

ced from tissue taken from a piece of leaf.

How then do leaf cells remain so orderly

and not suddenly start to make flowers or

fruits? This is because most genes are ‘swit-

ched off ‘. The DNA is folded up and packed

inside the nucleus. If a gene has to be read it

first has to be made accessible. Regulatory

proteins take care of this. They, as it were,

switch ‘on’ the gene. The stimulus to do

this comes from, for example, external

circumstances (such as climate) and plant

hormones.

It’s remarkable that the majority of DNA

doesn’t code for anything. It’s called junk-

DNA. This accounts for 97% of the total DNA

in humans.

Text: Ep Heuvelink (Wageningen University) and Tijs KierkelsImages: Wilma Slegers and Marleen Arkesteijn

All cells have the same genetic information

DNA: The recipe book for all the processes in the plant

During crossing genetic material comes from two sources creating a new set of double genes. The

breeder is not able to control whether a desired characteristic in the mother is passed on to the

offspring.

12-13-Thema7-IG-Onderzoek-basis1.indd 1 28-09-15 09:16


A particular feature of plants is that DNA is

not only present in the cell nucleus but also

in chloroplasts and mitochondria, the energy

factories of the cell. For example, the cell

nucleus in maize contains 30,000 genes,

the chloroplasts 125 and the mitochondria

40. This supports the theory that these cell

organs were originally bacteria that became

trapped, eventually leading to such a far-

reaching form of symbiosis that the modern

plant can no longer do without it.

Mutation by DNA damage DNA is reasonably well protected by its

double structure (the spiral staircase) but

damage can still occur, for example by

UV-radiation. This causes mutations, the

majority of which lead to the malfunctioning

of the DNA. However, very occasionally a new

characteristic is created. It means that in a

greenhouse full of white chrysanthemums a

pink one can suddenly appear. This is the

result of a mutation in a gene that is respon-

sible for colour. But most characteristics are

based on multiple genes, for instance, yield

is a very complex issue and can’t increase

drastically by just one or a few mutations.

Breeders take advantage of the natural

variation in a plant’s characteristics and

select the most favourable plant from which

to make further crossings. Sometimes they

damage the genetic material deliberately to

cause mutations from which they select a

few useful ones.

Breeding is time consumingBefore describing further the breeding

possibilities, we first need to explain some-

thing about chromosomes. Chromosomes

are the carriers of the genetic material and

are made up of DNA. In general, the genetic

information is available twice (diploid),

originating from the plant’s mother and its

father. However, pollen and egg cells are

haploid, that is they have only one set of

genes. It is pure chance whether the genes in

this single set originate from the mother or

the father.

During crossing (and therefore fertilisa-

tion of the egg cell) genetic material comes

from two sources and in this way a new

double set of genes is created. The breeder

can’t control if the desired characteristic in

the mother will be passed onto the offspring.

Firstly, it’s possible that the information

wasn’t passed on from the mother (but from

the father). Secondly, there are dominant and

recessive genes: the dominant genes are

expressed, not the recessive.

Thirdly, it’s often not that simple.

Sometimes both genes are expressed. In

addition, many characteristics are based

on multiple genes working together. For

all these reasons, breeding is very time

consuming work.

Genetic modification If you happen to find a wild variant with

resistance to a disease it takes a very long

time before you have a good cultivar. A

well-known procedure is to cross the wild

variant with an existing cultivar or parent

line and to cross the selected offspring (that

have inherited the disease resistance) many

times with the cultivar. This process can take

several years.

It’s very appealing therefore, to be able to

‘cut and paste’. This entails removing the

correct gene (or genes) for disease resistance

from the wild variant and placing it in an

existing cultivar that is performing well. This

is the process of genetic modification. In

plant breeding that happens a lot with help

from the crown gall bacterium (Agro-

bacterium tumefaciens). In nature, this

bacterium introduces genes into the plant

in order to make galls. Breeders use this

property during genetic modification.

The desired gene is first inserted into

Agrobacterium which takes it to the

plant DNA.

Much discussion There is much debate about genetic modifi-

cation. It is said to be much less safe than

DNA is the carrier of the genetic

information. This information is

encoded into a message which is

sent to the ribosomes which trans-

late the code and make proteins. All

cells have the same DNA but the

majority of the genes are switched

‘off’. That’s why, for example, no

fruits form on leaves. DNA some-

times mutates and as a result new

features may be created which

breeders take advantage of.

Summary

Figure. DNA transcription

1 Genetic information is read from the DNA

and converted into messenger RNA.

3 The cytoplasm contains amino acids.

Transport RNA carries them to the

ribosomes.

2 Messenger RNA leaves the nucleus and

goes to the ribosomes.

4 The ribosomes read the messenger RNA

and bond amino acids together to form

proteins (e.g. enzymes).

traditional crossing. However, the transfer

of a gene from a wild variant by genetic

modification is actually safer. You know

precisely what you are changing, which is

not the case with conventional crossing. The

situation is different when inserting foreign

genes (for example from a bacterium or

animal). This situation does not (or hardly

ever) occur in nature and there’s a large

degree of unpredictability in the final

outcome.

12-13-Thema7-IG-Onderzoek-basis1.indd 2 28-09-15 09:16

• Spores

• Tissue Culture

• Rapidly growing assortment

[email protected]+31 111 468 088www.vitroplus.nl

2016February

Experience Dutch innovation in horticulture

16 17 18

More info? Visit evenementenhal.nl/horticulture now!

Horticulture Business Days is proud to be considered the largest specialist Dutch horticulture nexus point. Are you ready to venture beyond your business borders?

In three days, we will welcome over 17,000 breeders, growers and associaties to our trade fair, from both the Netherlands and abroad.

An opportunity for you to expand your corporate horizon as a horticulture professional!

SCREEN SYSTEMS

Industriestraat 40 Postbus 245 2670 AE Naaldwijk The NetherlandsTel. +31 (0)174 62 94 44 [email protected] www.pdinl.com

GreenTechStand 11.116



General manager James Alcaraz at one of three transplanters that can transplant from virtually any plug tray into almost any pot or pack

configuration.

The UK would seem synonymous with garden roses. However, in recent years new housing developments have produ-ced much smaller gardens, traditional front gardens have been replaced with parking areas for cars. Therefore roses, like other hardy nursery stock has suffered and seen sales decline. Burston Nurseries, a major supplier of bedding plants and roses to the British garden centre industry, is bucking the trend by introducing ranges of modern roses, using innovative breeders and selecting only the very best.

Burston Nurseries has been at the heart of the

UK garden plant industry since it started tra-

ding in the 1963. Its late founder, John Pearson,

was a pioneering figure in the industry from

the 1950s onwards and one of the first chair-

men of the British Bedding Plant Association.

Also, its central location close to St Albans,

gives it easy access to major motorways for fast

distribution throughout the country. Today the

nursery covers around 10 ha including around 3

ha of glasshouses and poly tunnels, plus

offices, warehousing and cold storage facilities.

The nursery originally grew roses and later

on introduced bedding plants. Now around

70% of production is bedding plants and

30% is roses. It still produces well over 300

varieties of roses and a similar number of

bedding plants, mostly pansies, primulas and

polyanthus in the autumn and a full range of

summer plants from Non-Stop begonias to

geraniums and calibrachoa to surfinia for

the hanging basket market. These are sold

to shops, independent garden centres and

garden centre chains. “We also have a garden

centre onsite and this enables us to trial any

new products or varieties prior to going to

market in larger quantities,” says nursery

manager, James Alcaraz.

Text: Helen ArmstrongImages: Burston Nurseries

ROSESREPORT

Pioneer in bedding plants still at the forefront

Burston Nurseries grows roses from cuttings and breaks with tradition


15-17-Thema9-IG-Reportage-basis1-3pag.indd 2 28-09-15 09:21


amount of water. We’ve had this for three

years and it gives us confidence that the seeds

are being watered and they all receive the

same amount.”

When the seed trays have been filled they

are moved into the germinating room, a glass-

house which is set at 25ºC and 80% humidity.

“We’ve discovered that everything except

lobelia can be germinated in a stack so now

we stack trays on the trollies and once the

seeds have germinated we transfer the trays

to the floor.”

TransplantersGermination takes from a few days to two

weeks, depending on the variety. Once they’ve

reached a suitable size they are moved to

another room for hardening off before trans-

planting. “We use Tref Go propagation mix

which includes a clay substance. This binds

the plug together and forms a little bullet

around the root which makes the seedlings

much less susceptible to damage during

transplanting.

The nursery has three Hamilton-TEA

transplanters which are computer controlled

and can transplant from virtually any plug

tray into almost any pot or pack configura-

tion. The manufacturer is close by, which is

not only handy for servicing, it is also readily

available to reprogram for a new tray if

necessary.

“The transplanters will plant every cell,

although of course they are only as good as

the plug tray you give them. For example,

while we can reckon on 100 per cent germina-

tion from lobelias, some primulas, for exam-

ple, only have a 50 per cent germination rate.

A retail display at the onsite garden centre where new products or varieties can be trialled prior to going to market in larger quantities.

The company developed a range of roses that

grow on their own roots.


Roses from cuttingsThe market for garden roses has changed

dramatically over the last five to six years.

Less people are planting roses in gardens

although they are used for patio planting,

pots and balconies, says Alcaraz. The nursery

has been experimenting together with German

breeder Tantau Roses, near Hamburg. Over

the last three years they have developed roses

that can be grown from cuttings and that

survive and thrive in UK conditions.

“Tantau does the breeding and I visit yearly

to select the varieties that I feel are suitable for

the UK market. We then trial them here to

check they are compatible with our weather.

We have been using traditional cultivation

methods for roses for too long in the UK.

We are changing that and introducing some

brilliant varieties that will dazzle everyone. As

a result we’ve developed a range of roses that

grow on their own roots. In this way we can

manipulate the crop, similarly to bedding

plants, to flower when we want them to

flower,” he says. “We’ve also found that health

is much better and the roses flower for much

longer.”

It has a license agreement to take cuttings

itself and is now in the process of bulking up

numbers. “It’s a new way for us to produce

roses. We can produce large quantities in a

very small greenhouse whereas normally we

would need considerable amounts of fresh

land which is expensive and hard to find

locally,” says Alcaraz.

10 million seeds per yearOver 90% of the company’s bedding plants are

produced from seed within the nursery’s own

young plant facility. “We’ve been growing

young plants from seed since the 1980s. We

sow 10 million seeds per year and on a busy

day it can be up to 170,000. The ability to

produce our own young plants enables us to

be very competitive and flexible as we can

produce mixes of colours to suit customers’

requirements.

Burston is now on its second Hamilton

drum seeder. Seeds are fed into a hopper and

flow by means of agitation. A vacuum sucks

the seed onto small holes drilled into the

drum, as the drum rotates the seeds are

placed into the cells. The machine can be

programmed to virtually any tray size.

“The machine is brilliant. We are now on

our second one. We had to replace the first

one after 25 years. The technology has moved

on – everything is faster and it has an inte-

grated computer controlled watering system

which waters every single tray with a fixed


Burston Nurseries has been a pioneer

in the UK bedding plant industry

since the 1950s. Today it is changing

the way it produces roses. Not only is

this more efficient, it is leading to eye-

catching healthy varieties, designed

to buck the declining market. It has

the capacity to sow some 10 million

seeds per year and recently opened a

new cuttings facility.

Which variety? For West-European growers of greenhouse vege-

tables this period is a signal to choose your varieties.

But isn’t advice on this subject the same as kicking

in an open door? After all, we all know it’s a good

idea to opt for better-tasting varieties and the highest

possible quality instead of striving for the last extra

per cent of yield. However, it’s still the case that

not all growers are prepared to compromise a little

on yield to the benefit of quality and a satisfied

customer.

Encouraged by the seed companies, who against

better judgment bring the cheap and plentiful

varieties onto the market and even promote them,

many growers under pressure from low margins

choose a variety which they themselves wouldn’t

take home to turn into a tasty dish. Unfortunately

we’ve all come so far that in many cases this

decision is even understandable.

At least, that is, if you don’t look any further than

‘how will I get through the coming year’ because in

that case it really is only about highest yield at the

lowest cost. However, if you are planning to still

produce tomatoes or peppers for the next 20 years

then you’ll have to make choices that justify your

existence as a grower. That means choosing varieties

that aren’t going to disappoint the paying consumer

in terms of taste.

If you’ve chosen a product that you can be proud of,

which for example you can let visitors to the Grüne

Woche in Berlin taste without fear of their reaction,

then the next step is to bring the quality and taste to

a higher level. Because less kilos coupled to a poor

price returns twice as little and it won’t enable you to

pay the bills. Therefore visit the people who sell your

product and help them to bring your products to the

attention of their customers. And don’t be fobbed off

with “that’s not possible” or “people don’t want that.”

If we, as modern greenhouse growers, want to

maintain our right to produce, or perhaps I should

say ‘win back our right’ then we have to ensure that

together we establish a united level of quality; a level

at which we can surprise consumers and urge them

towards a healthier diet. We need to grow products

that the consumer deliberately chooses and not

just grow products to fill the increasingly seldom

shortages in the market. Product is needed for that

too but not so much. I wish all my fellow vegetable

growers much wisdom in their forthcoming choice

of varieties.

Frank van Kleef

Tomato grower at Harvest House

Column

17

We do ask breeders to test the germination

rates before we buy and sometimes we dou-

ble sow to ensure we get a seedling,” says

Alcaraz.

Most of the seedlings are transplanted

into polystyrene boxes, a small range of

two-litre and three-litre pots and increasingly

six-litre single and mixed containers, such as

a Trixie Mix, for the “bbq” market. All pro-

ducts are colour labelled and can be pre-

priced and barcoded.

New cuttings facilityOver the last 10 years there has been more

demand and need for bedding plants raised

from cuttings to be available for the end user.

“Our consumption of cutting raised plugs

reached a peak in 2014 at 800,000 plugs. This

was very expensive and as a result reduced

the overall profits. We have been experimen-

ting with rooting cuttings for the last three

years, with great success, so in autumn 2014

we built a new facility for sticking our own

cuttings and producing plugs.”

An old greenhouse of 1000 m2, was

rejuvenated with modern heating, lighting

and water systems. “The first crop went in

during the third week in January and we’ve

put through 550,000 plugs. Next years

production, which is sales led, is estimated to

be more than double, going up to 1.4 million,”

says Alcaraz. “We source cuttings from around

the world and ensure they come from a clean

source, we only buy material from reputable

sources that pay all royalties due to the bree-

ders,” he continues.

The cuttings are rooted in the same pro-

pagation mix as the seedlings and are placed

on the benches with underfloor heating

(20-22ºC) “We also build small plastic tents

within the greenhouse to create a micro

climate.” Cuttings take from around ten days

to three to four weeks to root and only when

rooted, trimmed and weaned are they ready

for machine transplanting.

Profitable cropsThe greenhouses are full for most of the year,

with just a lull in the autumn. “Production is

currently at capacity. However, we only want

to grow crops that are profitable.” Luckily the

nursery is able to run fluid staffing levels so

can easily increase or decrease numbers. “We

use an agency which supplies a lot of labour

from Eastern Europe. We provide an estimate

of our seasonal labour requirement but if it’s

a cold or wet season we can end the contract,”

says Alcaraz. “There is no point in having the

greenhouse full all the time just to keep the

staff busy.”

Summary

The glasshouses and poly tunnels, situated close to St. Albans, cover around 3 ha.




Exactly one year ago Wageningen UR Greenhouse Horticulture and a consor-tium of Dutch companies started buil-ding a new, energy-efficient greenhouse. The key component is a cavity roof, with ventilation, made of clear glass under which is a layer of durable diffuse film. This autumn those involved will weigh up its assets but it already looks like that this innovation will benefit Next Generation Growing. The system looks professional and visitors have reacted positively.

A group of growers are just ending their tour

through the tomato crop as researcher, Frank

Kempkes, and general manager, Arno van

Deursen of Van der Valk Systems, enter the

trial greenhouse for a photo. The growers

visit the 2SaveEnergy greenhouse in Bleiswijk

(Netherlands) weekly and advise on the next

cultivation strategy. “Of course they also

monitor the progress,” explains Kempkes.

“And up to now no technical problems have

occurred in the crop.”

Energy savingThis time too the group was satisfied. It was

11 May and the first day of summer weather

this year. The plants were in good condition;

a strong top, eight clusters of six fruits had

been harvested and a ninth cluster was in

flower. Only the setting of the fifth cluster

had been a little slow but it looked like the

crop (cluster tomato Capricia RZ) would

make it to November.

The aim of the trial is to use a maximum

of 19 m3 gas for the entire cultivation period

to harvest 63 kilo tomatoes per m2. This is

7 m3 less than the 26 m3 that was achieved in

a trial with a ‘standard greenhouse’ for the

Next Generation Growing. That had two

moveable screens, a fixed film in the start-up

phase and a dehumidification system that

used air sucked in from outside. If they meet

their target those involved hope to prove that

the energy efficient properties of the insula-

ted greenhouse roof will be an extra gain for

sustainable production. And they are well on

track: by mid May they had used just 8.8 m3

of gas.

Insulated cavityKempkes and Van Deursen are pleased that

the greenhouse actually does what they had

worked out on paper. Van Deursen: “Fortuna-

tely it works, because you devise such an

innovation for eventual use in practise. That’s

why we continuously take into account the

availability and suitability of the materials

and techniques that we are use during the

development phase.”

The concept works. The innovative green-

house is based on Next Generation Growing

and builds on the ID Greenhouse by Techno-

kas and Duijvestein Tomatoes, in the Dutch

Text: Jojanneke RodenburgImages: Studio G.J. Vlekke

DOUBLE ROOF RESEARCH

Next Generation Growing even more energy efficient

Affordable roof with high level of insulation and light transmission

Contrary to the plans made on paper, the trial greenhouse is equipped with a double glazed roof comprising clear glass and a diffuse foil. This

choice, motivated to provide assurance, is also financially beneficial.

18-19-Thema19-OG-Onderzoek-basis1.indd 1 28-09-15 09:22


village of Pijnacker, as well as other trials

with double glass. The 2SaveEnergy roof isn’t

made from double glass, that can be relati-

vely expensive, but instead from single glass

with high-quality film, which is integrated

into the roof as a sort of fixed energy screen.

The cavity between the two components is

achieved by the F-CLEAN film, which is fitted

on both sides with integrated strips, and is

pulled from a large roll, placed in one path,

over the entire length of the bay under the

roof bars. To achieve this the supplier may

need to make minor adjustments to existing

equipment.

Continuous roof ventilation The director points to the film: “Tight as a

drum. Even in warm weather it doesn’t sag.

Look, the profiles are equipped with special

guiding locks, which keep the film properly

in place, directly underneath the roof bars.

This creates a cavity of about 5 cm.”

Further to this technique, the consortium

– which comprises VDH Foliekassen, BOAL

Group and AGC Chemicals – and the research

institute also chose continuous ridge venti-

lation of multiple-coated, diffuse double AR

glass. “This roof ventilation is usually the only

special thing that visitors notice immediately.

You hardly see the cavity roof. You do notice

that the temperature here rises faster. Thanks

to the insulation effect the heat stays inside

and when the sun shines, the mercury rises

very quickly.”

Clear glass and diffuse filmConstruction of the greenhouse at Wagenin-

gen UR Greenhouse Horticulture started at

the end of June 2014. By mid-October more

than 470 m2 of the large construction work

was completed (4 bays of 4.8 meter and five

areas of 5 meter with a column height of

about 6 meter) and a crop of cucumbers had

been planted. We did have a delay, says Van

Deursen. “The biggest hurdle was the glass.

Our original plan was a combination of dif-

fuse glass and clear foil. After all, this allows

for the highest level of transmission. But what

happened, none of the glass suppliers could

give us sufficient information about the form

and drainage of any condensation that could

occur on the inside of the cavity.”

There is still little experience on this point

with diffuse glass. “And we certainly didn’t

want to take the risk of any moisture accumu-

lating in the cavity. So we turned it around:

Now the trial greenhouse has a cavity roof

made from clear glass and a diffuse film.

Funnily enough, later on we discovered

several benefits from having made this deci-

sion. It turned out that clear glass is 3 euro per

m2 cheaper – the price of diffuse and clear film

is the same – and when this diffuse film is

damp the transparency increases. So during

the winter months when you have a lot of

condensation, the film allows in more light.

And in the summer months the film is dry

and its diffuse property works optimally.”

Smarter screens A second point, in which the actuality is

different from the concept, is the introduc-

tion of a double screen. Kempkes: “Next

Generation Growing for greenhouse vegeta-

bles works optimally with two screens and

a fixed film during the starting phase. The

whole greenhouse is full of cloths and wires

and one way and another they obstruct the

light entering. We have already removed the

fixed foil because the roof is now insulated.”

Furthermore the discussion about the

screen installation and screen(s) got the con-

sortium thinking. Why not work with a cavity

screen? Van der Valk installed a double screen,

not on top of each other but with a gap of

5 cm. “The movable function gives growers

maximum control possibilities, a point, which

when it is a fixed screen, always generates

discussion. In the end, our greenhouse has less

screens, but we use them smarter.”

The techniques applied are working well,

given the good growth, cultivation and yield

of the tomato plants that were planted on 27

January. During the autumn of 2015 it should

become clear how the greenhouse performs

in terms of energy and cultivation and it

should highlight any points that could be

improved. After the ‘i’s have been dotted the

initiators of the greenhouse hope to be able to

build a commercial greenhouse. The system

is suitable for every type of Venlo green-

house, regardless of the crop, and it is a more

affordable alternative to double-glazing.

Cavity ventilation with greenhouse air It’s likely that the trial will be extended: It’s

a good opportunity to further research and

fine-tune the special characteristics of the

roof. “Among other things will be to work on

keeping the roof snow and ice-free, explains

Van Deursen. To achieve this the roof has a

special feature: active cavity ventilation with

greenhouse air. The gutters have openings

into the cavity where small fans can be con-

nected. Via hoses in the transom (transverse

horizontal bar in the roof construction),

which open when the vents are at the mini-

mum opening position, the air is blown back

into the greenhouse.

While the vents are in this position,

flexible rubber strip keeps them closed to

outside air. “Unfortunately we were unable

to test it last winter. Here, we would like to

make additional steps because it is a really

important point.”

Normally a greenhouse should be able to

bear a weight of 25 kilo snow per m2. But

because the snow doesn’t melt due to the

double-glazing, the value for insulated glass

is 50 kilo per m2. “That requires a heavier

construction and therefore higher costs and

less light in the greenhouse. Of course with

our concept we want to prevent that.”

An insulated greenhouse roof should

make Next Generation Growing even

more energy efficient. Parties involved

are developing a greenhouse with a

double glazed roof comprising single

glass and a film. The cavity that exists

between both layers creates a high

level of insulation with limited loss of

light transmission. The greenhouse was

completed in the summer of 2014 and

tomatoes were planted in January. The

crop is growing well and gas consump-

tion is certainly less than in the control

greenhouses.

Summary

Arno van Deursen (left) and Frank Kempkes and a cross section of the insulated greenhouse

cover. “The sector recognises that this innovation is both practical and affordable.”



Huisman Chrysanthemum in the southwest of the Netherlands produces 13 million Bonita stems annually. After switching to the new fertiliser

concept quality has remained high.

Chrysanthemum grower Peter Huisman has over the last year applied the Hori-zon fertilisation concept to his nursery in Maasdijk, the Netherlands. On one hand this strategy takes into account the emissions and the needs of the crop and on the other hand the structure of the ground. The biggest change for the grower is the method of administrating the fertiliser. “Previously we gave the necessary nutrients in the irrigation water, now we scatter over granules before we start cultivating. This stock of fertiliser then has to do its job. Quite exciting!”

After a one-year test period Huisman des-

cribes his experiences with the Horticoop

fertilisation concept. “Compared with the

usual methods Horizon is just as expensive

and the quality of the flowers is almost the

same. Let me put it this way: the crop is

certainly no worse. And that is good. In

addition I’ve noticed a visual improvement

recently in the upper soil layer. The structure

is slowly becoming looser.” Just like Horti-

coop’s product manager for fertilisers, Peter

Klein, and account manager, Arie Verloop,

the grower also believes that there is more to

gain from the ground. That was his reason for

trying this new fertiliser concept.

At the moment the trial is only being

carried on chrysanthemum nurseries. In

addition to Huisman, the trial involves two

other Dutch chrysanthemum nurseries. “I

believe that everything succeeds or fails based

on the structure of the soil,” says Huisman.

“Therefore this concept sounds very plausible

to me: When you’re fertilising you shouldn’t

forget about the soil. Also, my advisor from

DLV Plant had a good feeling about it. As an

independent professional he closely follows

the results and he gives me the necessary

objective feedback.”

Soil availability of minerals The intention is to roll out the concept for

other product groups. Lisianthias is likely to

be the first to join the programme followed

in the long term probably by alstroemeria.

Verloop: “It’s quite strange. We claim to be

such an innovative sector, but for decades

we’ve been using the same fertilisation

strategy for many cut flowers. During the

cultivation we dose everything out of the A-

and B-fertiliser containers and provide plenty

of water but otherwise growers hardly bother

any further. The result: over dosing and a lot

of fertiliser in the drain water.” In their search

for a more efficient fertilisation method the

Text: Jojanneke RodenburgImages: Studio G.J. Vlekke

CHRYSANTHEMUMREPORT

‘Everything succeeds or fails with structure of the ground’

Innovative fertilisation concept also looks at soil condition

20-21-Thema13-IG-Reportage-basis1.indd 1 28-09-15 09:24

A new fertilisation concept takes into

account both soil characteristics and

crop needs. The method includes

supplying the soil with a large stock

of fertilisers using an organic fertiliser

and regular Spurway soil analyses. In

addition to a healthy end product it

should also lead to more efficient

fertilisation of both main and trace

elements, less leaching and eventually

a better soil structure. Up until now

the concept has been applied only to

chrysanthemum cultivation.


horticultural supplier started to work with

Altic. This resulted in a tailor-made fertilisation

concept. “We call it a concept because it is

more than just applying fertilisers,” explains

Klein. “And it is innovative because we look

further than the current system. We begin with

a soil analysis. The results give us insight into

the structure and composition of the soil and

the availability of the minerals. From these

figures, we next look at the nutritional needs

of the crop. Based on this we accurately custo-

mise the fertilisation, including using a special

organic fertiliser.”

Good soil analysisGood soil analysis forms the heart of the

concept. The measurement is carried out

using the Spurway-method from Altic. While

traditional laboratory techniques focus on the

short term and the stocks, the focus of this

method is on the long term and actual availa-

bility. This method has been used a lot in the

last 15 years in practical trials and has shown

a strong link between the fertiliser applied

and measurements taken later during soil

analysis. By using this data reliable relations-

hips have been established between what is

measured regarding availability of main and

trace elements and the crop response.

For many crops this information provides

good insight into the relationship between

available elements and the actual uptake by

the crop. Klein: “And since our fertilisation

concept also focuses on improvement of the

soil structure, the current analysis has been

extended to examine the general characteris-

tics of the soil in the area which is to be

planted.”

80% pre fertilisationOn the 4.8 ha nursery belonging to Huisman

Chrysanten a new crop is planted 5.4 times

per year.

The new concept requires the grower to

have a fixed method of working. “Shortly be-

fore planting each new crop we have soil sam-

ples taken from the area concerned. Then

before the young plants arrive we scatter over

an organic fertiliser. This is tailor-made for

chrysanthemums and is in pellet-form.” By

using a small spreader behind the tractor he

can apply some 180 kilo per 1,000 m2.

The granules are mixed into the soil and

then humic acid is added to the first watering

so that there is less leaching of the fertiliser

and it is better available to the plant; it’s a

well organised and clear method that hardly

costs any extra labour.

With this pre-fertilisation the grower sup-

plies about 80% of the crop and soil require-

ments. The remaining 20% is supplied via the

usual fertiliser containers during the cultiva-

tion period. The results of the analysis deter-

mine its composition. Working with pre-ferti-

lisation takes the grower some getting used

to. “Luckily this concept also requires samples

to be taken during the cultivation, in any case

at least five times per year. In this way we

know for sure that no deficiencies occur and

we can make adjustments if necessary.”

More efficient application = less leaching By using this method to better balance the

crop with the soil, the account manager is

able to reduce leaching without damaging the

end product. “Current fertilisation strategies

provide the plant with 2.5 to 3 times the

amount it requires. Horizon is based on 1.5

times the need of the plant so is somewhat

more efficient. That’s important, certainly

considering the increasingly stricter rules

regarding emissions. Growers should easily

be able to reuse their drain water; the cleaner

the water, the better it is.”

Up to now the results appear successful;

the quality of the chrysanthemums remains

high and the soil conditions are improving

gradually. The latter should also lead to a

more active environment, more soil life and

thus better functioning of, for example,

natural predators. It takes time. That’s why

those involved are not planning to end the

trial quickly. Klein: “Only after prolonged

application of the concept can we be sure that

there are no longer any ‘old’ fertilisers in the

ground and the soil can regain its balance.

Then we can also attribute any other effects

to this method. For example, I believe I can

already see greener leaves at the bottom of the

chrysanthemum crop, but if that is actually

due to the new approach is too early to say.”

Summary

Peter Huisman (middle), Peter Klein (left) and Arie Verloop all decided it was time for a new

and innovative fertilisation concept for chrysanthemums.

Huisman spreads the organic fertiliser using a

spreader for synthetic fertilisers.


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Oscar Garza: “We have 60 ha, mostly tomatoes, but we want to grow to 100 ha. We also see opportunities in America and we want to be considered a

serious player.”

Investors in Mexico have just completed phase three of a newly established nur-sery that is producing cluster tomatoes, mostly for the US and Canadian market. Phase four is in the pipeline. The project began in 2010 and already covers 15 ha. The greenhouse for phase three was especially developed by its Dutch buil-ders and includes a newly designed alumi-nium gutter, durable insect netting that is integrated into the plastic cover and a new construction profile which signifi-cantly speeds up the building work.

Hydroponic Green Valley Produce is a relative

newcomer to the Mexican market. The Garza

family made the move into greenhouses just

five years ago having seen a synergy between

high tech tomato production and their gas

distribution company. With a strikingly dif-

ferent approach to traditional family produ-

cers, they immediately invested in high tech

equipment and wanted to scale-up as quickly

as possible.

Phase one was completed in 2010, phase

two in 2012 and the first plants went into the

third five-ha block in March this year. “Even

while we were constructing phase one we

were already taking into account the layout

for phase two so all the infrastructure was

based on 10 hectares,” says Edward Verbakel,

of Dutch greenhouse builder, VB Greenhou-

ses.

Top of the lineThe company cooperated with a Mexican

builder on the first two greenhouses and was

then given the contract to build the third

phase entirely. It had developed a new type of

plastic covered greenhouse, which was highly

Text: Helen ArmstrongImages: Green Valley

CONSTRUCTIONREPORT

Innovative greenhouse for high quality tomatoes in Mexico

New structure speeds construction and replacement of plastic cover




profile, which secures the plastic covering.

“Often, when the plastic is replaced every

few years people tend to use heavy tools,

such as a hammer, and end up damaging the

profile. Our long term partner for glass green-

houses, Boal Systems, designed for this pro-

ject a new profile which makes it so easy to

replace the plastic that it can be done many

times without causing the usual damage,”

says Verbakel.

Aluminium gutterThe aluminium gutter is another new feature

not normally seen in plastic greenhouses. The

advantage, just like in a glasshouse, is that

when condensation forms as the warm air

hits the cold metal surface, it can be collec-

ted. “Even though more condensation tends

to form in a plastic greenhouse than a glass-

house, until now it has not been possible to

drain it off effectively. Boal designed a new

model that allows this to happen and the

gutter is integrated into the construction

profile,” says Verbakel.

The aluminium gutter collects condensa-

tion as well as rainwater at both ends of the

greenhouse and is then transported by pipe-

line to a foil-lined irrigation reservoir of

18,000 m3. An additional condensation gutter

is integrated below the aluminium gutter to

collect condensation that is formed under-

neath the gutter itself.

Double plastic coverThe greenhouse is covered in a double layer

of plastic, which has air in between to pro-

vide a high degree of insulation – certainly

more so than single glass. This is an advan-

tage in the winter when the night tempera-

ture can drop to minus 10ºC as the greenhou-

ses are situated on a high plateau, 2,000m

above sea level. The cold nights are also the

reason why they installed an energy screen.

They also have boilers that supply CO2 during

the day and provide heat, which is collected

in water storage tanks, for night usage. The

two heat storage tanks of 2500 m3 each are

large enough to be able to serve 20 ha by the

time phase 4 is finished.

The growers choose plastic above glass

because the light intensity in this area of

Mexico is so intense that if the greenhouse

had been made from glass you would need to

apply a whitewash or coating for most of the

year, says Garza. This treatment would need

to be repeated during the season, increasing

the costs and labour requirement. This is not

necessary with the plastic covering. A further

advantage is that the plastic diffuses the light

somewhat, improving growth as light

penetrates the crop further.

Durable insect gauzeThe grower says he was also keen to install

insect gauze because the nursery is in an area

The greenhouse is covered in a double layer of plastic which, thanks to a new profile in the

construction, is easy to replace when necessary.

The continuous ridge ventilation has extra

large vents that are fitted with harmonica

insect gauze.


suitable for the area around Saltillo, near

Monterrey.

“We saw that the US market was con-

stantly increasing its quality standards and

certification requirements,” says Oscar Garza,

managing director of Hydroponic Green Val-

ley Produce. “From the beginning we pictured

ourselves selling to clients at the top end of

the market, competing in quality and fresh-

ness with the best Canadian or US producers,

and being able to deliver year round. We

could only achieve this by having the top of

the line technology available, and this new

greenhouse provided better solutions to our

needs,” he says.

In his previous experiences with phase 1

and 2, Garza was very involved with the VB

Group in all the planning, layout design and

construction. “And I learned a lot about how

we could improve for the next phases. We

focused a lot on construction efficiency, with

fewer connections, less people to bring it up

and less heavy equipment needed.”

More kilosThey started laying the foundations in Octo-

ber and the construction was finished within

two months. The interior was completed

during January and February and the first

plants went in on 1 March. The plants are in

hanging gutters in Riococo substrate slabs,

made from Coco peat. The first cluster toma-

toes, of the non-grafted variety, Merlice, were

harvested in early May.

Garza hopes they will produce a higher

yield than the previous greenhouse because

of the capability to produce year round, only

stopping to change the plastic cover when

needed, “It will certainly out-perform the

previous greenhouses; we expect 15 to 20 per

cent more kilos,” he says.

Faster construction“We knew we could complete the construc-

tion quickly due to the better design of the

connecting elements,” says Verbakel. The steel

bow that holds the systems above the gutter

has three holes, one that holds the ridge and

two to hold the gutters. “In previous green-

houses there were 12 connections so now we

can build much faster. Also, the aluminium is

extruded in such a way that it requires fewer

nuts and bolts. We were able to reduce the

speed of construction by one third which

saves on local labour and supervision and it

can make a considerable difference to the

planting date of a project,” he says. The reduc-

tion in materials also means that more light

can enter the greenhouse.

Another significant feature is the redesigned


Hydroponic Green Valley Produce is

a relative newcomer to the Mexican

market. It has invested in high tech

greenhouses to produce year round

tomatoes and be able to compete with

the best producers in the American and

Canadian market on quality and

freshness. The design of the plastic

covered greenhouse reduces construc-

tion time and its innovative features

include an aluminium gutter to collect

rainwater and condensation and an

integrated durable insect gauze.

25

with a lot of agriculture and is regularly ex-

posed to large swarms of insects, for example

during the maize harvesting. However, insect

gauze often leads to problems when replacing

the plastic covering as the profile tends to get

in the way. Again the Dutch partner was able

to design a new profile that makes it much

simpler to replace the plastic.

“We have installed double continuous

roof vents that run the length of the house

into which is set an integrated harmonica

insect system of very fine gauze. This has a

mesh opening of 0.4 x 0.7 mm with 14 folds.

Also the window vents are extra-large and

measure 2 meter long with openings of 1.75

meter in order to improve air exchange. The

bays measure 9.6 meter so you see the vents

are extremely large. Each one has an indivi-

dual motor so they can be operated individu-

ally,” says Garza.

The gauze has a long lifespan due to its

high resistance to UV-radiation. UV-radiation

often causes normal gauze to deteriorate ma-

king it susceptible to breakage so that insects

are able to enter.

Bear crop loadIn order to supply cluster tomatoes year-

round the company decided from the begin-

ning to implement interplanting. This meant

that the double crop load needed to be taken

into account during the construction. To

confirm that the structure could carry the

weight, VB Greenhouses had the calculations

independently verified by the Dutch Institute

TNO. “We wanted an independent institute

to confirm that the construction could bear

the weight of the crop load as well as the

screen and the pull wire system and be wind

resistant. We wanted to prove its reliability,”

says Verbakel.

Marketing organisationThe technical area is located between the

greenhouses likewise the hub for the complete

logistical system. The harvesting carts are

brought here and the tomatoes are weighed,

packed and put in cold stores in readiness for

distribution to the USA, apart from the small

percentage that goes to the local market.

Hydroponic Green Valley Produce has

joined forces with a few other Mexican

growers who meet the same quality standards

to establish their own marketing and distribu-

tion company. Under the name GlobalMex

the growers represent about 60 ha, mostly

tomatoes, although their ambition is to

strengthen their position and grow to 100 ha

Summary

In the new greenhouse, variety Merlice, aluminium gutters are integrated into the construction profile and collect condensation as well as

rainwater.


and diversify with other crops, says Garza.

“We see opportunities in America and we

want to be considered a serious player. While

the trend there is for locally produced produce

we know that with our labour and climatic

advantages we can be as good, providing we

have high standards and that we monitor and

secure all systems in the greenhouse environ-

ment, which can only happen if we invest in

high levels of technology.”



A consortium of companies, together with Wageningen UR, is developing a green-house that will maximise the amount of light entering between October and March. The goal is to achieve 10% extra yield during these months. The gain in light should come from a combination of various adjustments and improvements. Following the theoretical simulation models and physical scale models, the first winter-light greenhouse will be built next year as ‘proof of principle’ at the Innovation- and Demonstration centre in Bleiswijk, the Netherlands.

During the winter, when the natural light

level in West-Europe becomes the limiting

factor for growth and yield, the prices for

horticultural products are at their best. That’s

why growers and greenhouse builders asked

researchers to design the ideal ‘Winter-light

Greenhouse’.

Project leader Frank Kempkes distinguis-

hes three stages in their search for this green-

house concept. Firstly they needed to confirm

which features play a role and from that

calculate some greenhouse concepts. In the

second phase, researchers used scale models

of greenhouse roofs to validate the simula-

tion model and measured light transmission

when condensation (wet glass) was present.

In the last phase the ‘best’ winter-light green-

house will be built.

Effect on light transmissionThe research project is funded by Greenhouse

as Energy Source, the innovation and action

program run by sector association LTO

Glaskracht Netherlands and the Dutch Ministry

of Economic Affairs. A consortium of compa-

nies, comprising Bom Group, Glascom Horticul-

ture, Bayer Cropscience and Ludvig Svensson,

will design and develop the greenhouse. The

different consortium partners are working on

different components, such as the develop-

ment of a ‘winter-light ‘ cucumber crop that

doesn’t produce unnecessary leaves or screens

with an even higher light transmission.

“During the summer of 2014, we deter-

mined which features play a role in light

transmission in the winter when light is the

limiting factor. These include angle of the

roof, direction of the ridge, asymmetry,

arc-shaped greenhouse roofs, different types

of anti-reflective coatings, diffuse and clear

glass and the reflection value of the structural

parts in the greenhouse,” explains Gert-Jan

Swinkels, researcher greenhouse climate and

energy. Regarding the direction of the ridge, in

general a north-south direction is favourable

but during the winter an east-west orientation

is more beneficial, also with diffuse glass.

Simulation modelThe researchers varied the slope and form of

the roof: symmetrical, asymmetric or

curved. They also looked at the effect of

various AR-coatings. Most coatings increase

the transmission especially at low angles, but

in the winter it’s actually the very high angles

(greater than 60º) of incidence that are impor-

tant. The angles indicated are relative to

perpendicular. “We used these properties to

calculate a large number of greenhouse

concepts. These calculations were carried out

using a ray-tracing simulation model. This is a

realistic simulation of the transmission of light

through a greenhouse roof,” says Kempkes.

Text and images: Marleen Arkesteijn and Wageningen UR Greenhouse Horticulture

LIGHT TRANSMISSIONRESEARCH

Effect of condensation still being researched

Extra light and save energy in ideal winter-light greenhouse

Trials have been set up to measure light transmission in dry conditions. The aim is to develop a winter-light greenhouse that allows maximum

light penetration from October to March.



For each concept they calculated, on the

basis of the predicted transmission values

and hourly radiation (direct and diffuse), the

total amount of daily natural light in winter.

This first calculation phase took six months,

from March/April to September. Important

conclusions emerged that allowed Kempkes

and Swinkels to progress further.

More winter transmissionThe aim is to achieve 10% better light trans-

mission. In the winter an east-west orienta-

tion of a Venlo roof gives 2 to 4% more light

than a north-south direction. The most opti-

mal slope for an east-west orientation lies

between 20 and 25°. There is hardly any gain

in light when using diffuse glass on an

asymmetrical saw-tooth greenhouse roof,

with the standing side-facing south, yet up to

4% for clear glass. A greenhouse construction

with a high degree of reflection can yield 3 to

6% more light.

“We’ve tinkered with the shape of the

gutters, glazing bars and ridge. By optimising

an existing angle-dependent AR-coating, in

theory it is possible to achieve a seven per

cent gain in light, at the same overall hemisp-

heric transmission,” says Kempkes. “The pro-

duction of such a coating is still a challenge.”

The model calculations work with many

degrees of freedom, so many independent

parameters. This showed, for example, that

a saw tooth roof does have construction

constraints. The long glass planes need an

extra purlin and more glazing bars for

support, which lead to less light transmission

instead of more.

Model greenhousesUp to now everything described was theore-

tical. To check if the model calculations were

correct the researchers built scale models of a

Venlo and saw tooth roof with various sur-

face areas of construction parts combined

with clear and diffuse glass. A light sensor

was placed both in the open field and under

each scale model to measure the light trans-

mission over a longer period and to make

comparisons with the model calculations.

Swinkels: “There seems to be a good match

between the model and the measurements

from the scale models. Thus the simulation

model is very useful as a tool to calculate the

design of the final winter-light greenhouse.

We have also added the laboratory measure-

ments on the glass and the refection measure-

ments for the greenhouse construction to the

model. It involves spectral transmission,

reflection and the light scattering from the

material under all angles of incidence.”

One of the unexpected insights gained

from the trial with the scale models raised

the question: how diffuse is the cloud cover

actually? It appears that the height of clouds

does make a difference. Low hanging cloud

makes light more diffuse than cloud higher

in the sky. This requires possible adaptations

to the existing models.

CondensationThe measurements show that condensation

has a big impact on the light transmission of

glass. But not much is known about it except

that windows in winter are almost never dry.

“We did some research on condensation seven

years ago,” continues Swinkels. Then, with

trials set up in a climate cell, we measured

differences of +2 to -5%.

Taking reproducible measurements on

condensation turned out to be a real chal-

lenge. “Because little is known about the

effect of condensation on light transmission

through different types of diffuse glass, we

set up a trial in a greenhouse in Bleiswijk.”

Here the researchers can look at five different

sorts of glass in dry and wet conditions: clear

glass without coating, two types of diffuse

glass with a pyramid structure from different

manufacturers (of which one has the struc-

ture on the inside and the other on the

outside), etched diffuse glass and various

AR-coatings to mimic hydrophilic and

hydrophobic effects.

Effect of condensationThe trial greenhouses in Bleiswijk have

eleven panes in a single continuous vent in

the ridge. Swinkels: “We’ve measured five sets

of two: dry and wet. Under each pane is a

PAR-sensor. The cultivation strategy is warm

and humid with frequent use of atomisers.

Therefore there is certainly condensation

on the greenhouse roof. The ‘dry’ glass is

kept dry by blowing through warmed air. A

V-shaped structure ensures that no condensa-

tion falls from above onto the area being

measured. The dry windows allow for com-

parative measurements.”

The results are currently being analysed

and visually there are large differences in the

form of condensation between the different

panes and that will most likely also affect the

transmission. Of course, with the current

modern greenhouses, as much as possible is

already taken into account regarding light

transmission. So for the winter-light green-

house all the stops have to be pulled out to

achieve the target of 10%. At the moment the

researchers are considering the use of new

materials and the design of the construction,

all of which takes time. It is expected that

the construction of the winter-light green-

house will start in the summer of 2016.

Research should lead to the ideal

winter-light greenhouse for Western

Europe that will allow the maximum

amount of light to penetrate from

October to March. The target is 10%

extra yield. Last year by using a

simulation model researchers calcula-

ted how different greenhouse con-

cepts and components could contri-

bute to better light transmission. A

Venlo roof in an east-west orientation,

with a slope of 20 to 25º, a construc-

tion with a high reflective value and

an angle dependent AR-coating made

a positive contribution to better

transmission. Construction of the first

winter-light greenhouse will start in

the summer of 2016.

Summary

Frank Kempkes (left) and Gert-Jan Swinkels: “By taking measurements from scale models we

checked if our calculations were correct. The goal is to achieve 10% extra yield with the winter-

light greenhouse.”



Nursery manager Remco Vijverberg sets the sensor, which hangs in the crop, to the correct gas concentration.

Ripening the last tomatoes at the end of the season is often a problem. By using a controlled administration of ethylene gas it is possible to stimulate the ripening process. Tomato nursery Van Heijningen of Maasdijk, the Netherlands, has had some good experiences with it.

Brothers John and Johan van Heijningen

grow loose tomatoes on 11.2 ha of rock wool

without artificial lighting. In this traditional,

year-round system production begins in late

February and runs through until the begin-

ning of November. Then the last tomatoes

need to have been harvested because they

start planting the new crop. Previously, to

ripen the last tomatoes, they sprayed the crop

with ethrel one week before the end of the

cultivation period.

“These ripened fruits were red on the outside

but when you cut them in two they were still

green on the inside,” says nursery manager,

Remco Vijverberg. “In terms of quality this

was not an optimal product and it was sepa-

rated into special containers by the trade. And

you had to be really careful that you didn’t

exceed the Maximum Residue Level (MRL).”

Ethylene treatmentWhile looking for an alternative to ethrel

spraying the tomato nursery came in contact

with Restrain Ethylene. This generator uses a

catalyser to convert ethanol into ethylene gas.

A sensor determines just the right concentra-

tion to use to stimulate the ripening process.

The Ctgb – the board in the Netherlands that

authorises the use of plant protection

products and biocides – granted permission

to use this gas in the Dutch tomato sector at

the end of last year.

By using a compact ‘plug and play system’

it is possible to administer a low dosage of gas

in the greenhouse during the last weeks of the

tomato crop. This ensures that the last clusters

also ripen properly. “By using this one hundred

per cent natural application a tomato grower

can harvest an extra one to one and a half

clusters per plant, without any residue,” says

Paul O’Connor, of Restrain. “Also, by adminis-

trating the gas you accelerate the ripening of

the last clusters, so the crop can finish earlier.”

This can save 0.5 to 0.75 m3 gas per m2.

ResearchResearch into this treatment with ethylene, a

natural maturation hormone, was first carried

in 2011 at the request of a nationwide commis-

Text and images: Harry Stijger

RIPENINGREPORT

Good alternative to spraying with ethrel

‘ Ethylene gives you better controlover the ripening of tomatoes’


Treatment with ethylene gas is a

good alternative to spraying with

ethrel for the ripening of tomatoes.

The quality of the ripened tomatoes

is better and it does not lead to any

residues. More clusters can mature

and ripen at the end of the crop. A

rise in temperature, such as that

required for ethrel, is not necessary.

In addition to saving energy, tomato

nursery Van Heijningen also makes

savings on labour.


sion of tomato growers. This had to do with

the negative press coverage at the time and

the pending ban on the use of ethrel, due to

its toxicity and the possible carcinogenic

effect of the active substance, ethefon.

The first research project began in

November 2011 with the variety Komeett and

compared an area in which the fruits could

ripen naturally with an area that was treated

with the gas. The same temperature regime

was maintained in both research greenhouses

in Bleiswijk, the Netherlands. “The ripening

process of tomatoes was stimulated by

ethylene, after which the fruits started to

produce the substance themselves,” says Jan

Janse, researcher at Wageningen UR Green-

house Horticulture.

Ripening effectAfter three days of dosing with the ethylene

gas they reached a level of 1.3 ppm. In nature

this is usually about 0.3 ppm. The researcher

reported the following observations: “Compa-

red with the non-treated area there was a

clear visual effect on ripening. There were no

signs of wear on the crop that you sometimes

see after spraying with ethrel. There weren’t

any differences in shelf life or internal

colouring of the fruit. The untreated tomatoes

showed more variation in colour within a

cluster; colour was more uniform after the

ethylene treatment.”

One year later, in November, more exten-

sive research was carried out in the two green-

house sections. As well as untreated and

ethylene treated, this trial also included

ethrel. In accordance with the requirements,

ethrel was sprayed on the crop when it still

had two to three clusters. During the dosing

of the ethylene gas the aim was to achieve

1.3 ppm; 1.4 ppm was realised within five days.

The same temperature regime was main-

tained in each research section: first high and

then lower.

EvaluationJanse: “The crop that was sprayed with ethrel

deteriorated faster, had more yellow stems and

more stem botrytis. The colour of the toma-

toes was similar for both treatments, especially

for the first unripe cluster. In this trial the

clusters higher up ripened slightly faster when

treated with ethrel. The largest colour varia-

tion was within the cluster on the untreated

plants.”

No difference in taste and refraction (Brix-

factor) was noted between the treatments.

The treated tomatoes had a better shelf life

than the untreated.

More clustersTomato nursery Van Heijningen applies

ethylene to ripen the last fully developed

clusters. They start to dose one month before

the end of the cultivation period. Vijverberg:

“During the last month there are five clusters

that you can allow to ripen faster. When using

ethrel you can only harvest two clusters. In

addition the day temperature has to rise from

17 to 22 degrees C in order to have the green-

house empty one week after spraying. When

using ethylene no rise in temperature is

required, so no extra energy costs.”

The gas is only dosed at night. Application

starts around 23.00 when the vents have all

been closed. This continues until 7.00 the

next morning and then the house is ventila-

ted again to activate the plant to start assimi-

lating. “The gas stops the plant assimilating

but growth must still continue.” The crop and

tomatoes continue to grow during the day

without ethylene.

Change of crop The nursery manager starts with a set point

of 0.5 ppm. After a week he checks how the

ripening is progressing. After ten days he

increases the dose to 1 ppm, and in the last

week up to 1.5 ppm. The possible final step,

five days before the crop changeover, is to

switch from night-only to 24 hour dosing.

“If all goes well with the ripening you

can simply continue with the same low dose.

If not, for example when it is cold and dark,

you may have to increase it sooner. With this

system you can control the ripening much

better,” says Vijverberg. “This is positive be-

cause everything is calculated to the date at

which the greenhouse has to be empty. The

change of crop is important for a grower

because the contractor and new plant mate-

rial have already been ordered.”

Measuring the concentration The manager has noticed better development

and quality of tomatoes after using ethylene.

This leads to fewer problems with the pro-

duct in the trade. The treatment also saves

four hours labour per hectare which other-

wise would be needed to spray the ethrel.

The fans in the greenhouse spread the gas

throughout the greenhouse very quickly and

well. Using a handheld sensor Vijverberg

measures the values before and after ventila-

ting to see how quickly the air in the green-

house returns to a normal value.

Summary

Jan Janse (left), Remco Vijverberg and Paul O’Connor (right): “Ethylene stimulates the ripening of

tomatoes but the crop doesn’t show any sign of wear as happens shortly after spraying with ethrel.”

The generator uses a catalyser to convert etha-

nol into ethylene gas.



In new greenhouses standard float glass has already made way for toughened diffuse glass with a coating. To make the most of the light gain, regular cleaning is essential. But how should you clean the glass without damaging it?

In addition to standard float glass, several

types of glass are now available for the

greenhouse roof: toughened, coated and

diffuse glass. Diffuse glass is made ‘perma-

nently’ diffuse by using rollers or etching.

Several different types of glass coatings are

available such as anti-reflective (AR), energy

saving or sun reflecting. Each type of glass

with special characteristics requires correct

cleaning to avoid losing its specific activity.

When choosing which type of glass to use

for the roof, cleaning plays an important role.

“How well and simply can you clean the

glass?” is the question always asked by Jos

Koop, project leader DLV glass & energy, the

Netherlands. “Because if a grower doesn’t

regularly clean his roof its generally 3 to 4 per

cent dirty. This light loss has a negative impact

on the yield.”

Guarantee on coated glass Regarding the choice of glass, the project

leader says, “Coated glass must withstand the

normal greenhouse conditions of moisture,

plant protection and cleaning agents, without

becoming damaged. Actually, suppliers and

glass manufacturers should provide a certifi-

cate or a written guarantee. Growers should

not have to encounter any problems with the

glass if using a coating solution for at least 15

years, the economic lifespan of a greenhouse.

If there is no certificate or guarantee the

grower shouldn’t choose that glass.”

Koop knows that condensation between

glass panes produces an etching effect. “Be-

cause there is absolutely nothing else con-

tained in condensation water it has a great

ability to dissolve substances. Therefore

growers must take care that spare glass is

stored in a dry place. Manufacturers use a

layer of white powder, such as titanium

oxide, between the panes to protect the

glass. In the past they used to put a sheet

of paper in between.”

Types of diffuse glassAccording to Koop growers can choose from

two different types of diffuse glass. The first

type is ‘prismatic’ glass into which has been

rolled small pyramids or other forms to make

it uneven. Examples of this include Vetrasol

502 and 503. The second type is micro-etched

glass, which has been roughened by using a

solvent. This type of glass is available with

a level of diffusion (haze-factor) from 10 to

90%. For a more accurate indication of ability

to diffuse light Wageningen UR Greenhouse

Horticulture developed a new value: the

F-scatter. This indicates the distribution of

the light.

Koop: “The distribution of light by the

micro-etched glass is better than that of

prismatic glass. The glass becomes dirty more

quickly and it is more difficult to clean than

the micro-etched glass. By laying the diffuse

side of the prismatic glass on the outside of

the greenhouse roof it becomes dirty more

quickly but it is easier to clean. When it’s on

the inside it becomes dirty less quickly but it

is more awkward to clean.”

Damage to glass types Solutions containing fluoride are certainly

not suitable for cleaning toughened, coated

or diffuse glass. The cleaning and etching

effect of fluoride not only dissolves the dirt

but also a miniscule layer of glass. Due to this

roughening effect the glass becomes dirty

even faster. After repeated applications the

glass becomes mat which also leads to light

loss.

With diffuse glass it is also possible to

damage the structure of the glass. Laboratory

tests on toughened glass have shown it is

affected by fluoride-containing products and

these cause a light blue haze on the glass.

Fluoride containing products irreparably

damage the coating on coated glass. Even if the

coating is on the inside of the glass, droplets

can seep through to the inside during cleaning

and damage the glass. High-pressure hoses can

also damage coatings.

Remove chalkOxalic acid or citric acid can be used as clea-

ning agents to remove dirt and chalk. These

products don’t produce any vapour and don’t

affect normal glass. Special cleaning solutions

are available for removing specific shading

products.

Glass that is coated on the outside cannot

of course be coated with a layer of white-

wash. The whitewash removers can eventu-

ally affect the properties of the coating. For

example, sodium hydroxide solution does

affect the AR-coating.

Koop: “Growers who want to whitewash

the greenhouse roof must select glass that is

coated on just one side and lay the coated

side on the inside of the greenhouse. The

outside can then be coated and cleaned later

with a remover. If the glass is clean, with a

coating on one side only half the extra trans-

mission will be achieved.”

Clean waterGrowers are advised to ask the manufacturer

or glass supplier about which cleaning pro-

ducts are most suitable to use. In addition, it

doesn’t hurt to first test a (new) solution on

both sides of one window pane. After such a

trial treatment inspect the glass for any

damage and for its clearness before conti-

nuing to use the solution. Also, it’s always


CLEANING GLASSFEATURE

Project leader Koop warns about light loss

‘ When choosing a glass type also consider the cleaning of it’

Jos Koop (links) and Cock van Schie: “The green-

house roof cannot be completely cleaned with

just one wash per year.”

30-31-Thema4_OG-Achtergrond-2-pag.indd 1 28-09-15 09:40

When choosing a type of glass gro-

wers should also consider how they

should clean it. Coated glass needs to

withstand the normal greenhouse

conditions of moisture, plant protec-

tion and cleaning agents, without

becoming damaged. Suppliers and

glass manufacturers need to provide

a certificate or written guarantee for

this, because if cleaning solutions

damage the coating then the extra

investment is lost.


good when hiring in a contractor to inform

him about the special glass on the roof.

To prevent a solution damaging the spe-

cial glass, the only really safe way to clean it

is to use warm water. However, cleaning just

once will not be 100% effective, therefore it

is recommended to clean it several times per

year. The outside can be best done using a

roof washer. The cleaning brushes should not

be old and dried out but clean and made

from soft bristles.

Cleaning greenhouse roofTomato grower Cock van Schie, of Westland,

the Netherlands, has standard float glass on

the greenhouse roof. During the crop change-

over, sprayer contractor, Paul Sosef cleans the

inside of the roof with a mechanical sprayer

using a 1% fluoride solution and soon after-

wards rinses it off again. Van Schie: “By kee-

ping the greenhouse windows closed the

night before we clean we ensure that the glass

is damp. For as long as the glass remains wet

and the fluoride is only on for a short period

all the dirt is removed from the glass and the

roughening effect is kept to a minimum. The

windows are then cleaner than when we use

oxalic acid or citric acid.”

The outside of the greenhouse is cleaned

in February or March by contractor, Jan Poot,

who uses a roof washer and cold water. The

roof washer also brushes the gutter clean.

Take the weightThe grower has noticed that the moss gro-

wing in the gutter and along the roof rods is

not completely removed when the roof is

cleaned just once per year and grows back

again, especially in the summer. “Then you

have to clean the roof a second time in the

year, for example in September, but that

costs a lot of money on 10 hectares.” Van

Schie has considered buying his own roof

cleaner but the investment in a fully auto-

matic machine is very high.

Koop says that a roof capable of carrying

a roof washer should be able to bear 600kg,

as calculated by TNO. “A grower should

reckon on 2,000 kg for the extra burden on

the end wall. This is the combined weight

of the docking station and roof washer that

rides along the gutter rail.”

Summary

Various contractors clean the inside of the greenhouse roof during the crop change-over using a mechanical spray trolley. This sprays the glass

with a fluoride solution and very soon afterwards rinses it off.

It’s not possible to completely remove moss gro-

wing in the gutter and along the roof rods with

just one wash per year.

30-31-Thema4_OG-Achtergrond-2-pag.indd 2 28-09-15 09:40

128 PAGES PLANT PHYSIOLOGY

Order at: www.ingreenhouses.com/books

PLANT PHYSIOLOGY

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€ 75+ shipping costs

Plantkundeboek-adv-124pag-2015-ENG.indd 1 20-03-15 10:57IG4-Oktober2016-ADV.indd 1 28-09-15 10:25


Phytophthora is a very common genus of pathogens whose many specific species

affect both the roots and parts of the crop above ground. Just like Pythium, it belongs

to the so-called class of water moulds. The characteristic of water mould is that it lives

on organic material and as a result damages the plant. Water moulds, also known as

oomycetes, require an individual approach when using chemical control. Therefore

it’s important that the diagnosis clearly shows the cause of a certain wilting or dis-

coloration.

If plants go limp and lose their leaves in the summer then treatment rarely succeeds

in reviving severely infected plants. When Phytophthora capsici attacks sweet peppers

then the removal of diseased plants is sometimes the only option. It is recommended to

remove these plants hygienically: This requires putting every diseased plant directly

into a leak-proof bag and then transporting it to a waste container.

Plants in the vicinity of the plant that has been removed can be treated with an

anti-Phytophthora substance if necessary. In addition, it is advisable to disinfect the

area around the cleared plants to limit the spread of the fungus further.

.

Phytophthora

Text and images: Groen Agro Control

PESTS AND DISEASESIN GREENHOUSES

33-Thema22-OG-Plagen-BASIS.indd 1 28-09-15 09:41


The photosynthetic process can hardly be bettered. But the utilisation of natural or artificial light certainly leaves room for improvement. In recent years our understanding of light has grown considerably and this has major impli-cations on how we deal with light in horticulture.

Light that falls onto a plant represents a

hefty chunk of energy. The plant can do three

things with it. First and foremost, of course,

photosynthesize: The utilisation of solar

energy for the production of assimilates.

The solar energy excites an electron in the

chlorophyll (the substance that makes the

plant green) taking it to a higher energy level.

During a whole chain of reactions it falls

back to its original level. In doing so the

trapped energy is transferred into all sorts of

chemical substances and eventually is used

to convert water and carbon dioxide into

sugars.

FluorescenceHowever, the electron can immediately

return to its lower energy level. Then it

emits light. This second effect is called

fluorescence. The plant always fluoresces

somewhat, but when this happens at a high

level something is wrong with photo-

synthesis. The plant is then unable to use the

majority of the light to produce sugars. This

happens when there is too much light, but

also if those sugars already produced cannot

be sufficiently transported away. The latter

occurs if the sugars cannot be transported

to enough places, such as developing fruits,

young buds or flowers.

The third effect of light is to heat the

plant. These three processes – photo-

synthesis, fluorescence and heating – all run

next to each other. Of course, as a grower, we

want plenty of photosynthesis because this

means production. We don’t need to worry

about trying to improve the photosynthetic

process because this is out of our control. But

because the light in the greenhouse is often

below optimum, artificial lighting is a good

way to improve production and quality.

Furthermore, there is no longer any doubt

that diffuse light improves both yield and

quality.

Photo-inhibition More light, however, is not always better.

At a certain level, photosynthesis is at its

maximum and part of the light is not utilised.

Firstly photo-inhibition occurs: The photo-

synthetic system is temporarily ‘full’,

whereby the plant not only starts to fluoresce

more, it also heats up. The situation recovers

when the light level falls and the plant

functions normally again. But at an even

higher level so-called reactive oxygen species

arise which cause irreparable damage to the

photosynthetic system.

In particular, pot plant growers are very

apprehensive about light damage and for this

reason frequently use screens and white-

wash. They tend to use light levels lower

than necessary so photosynthesis is still a

long way from its maximum and therefore

they forfeit production. However, research

shows that many shade plants can handle a

higher light level than is usual in practice

and grow much better and are available for

delivery faster. A condition is that the

humidity remains relatively high (75-80%) and

the temperature doesn’t rise too much. The

combination of a high light level, high tem-

perature and low humidity does damage the

plant.

More efficient lighting For many crops extra light offers many

benefits. With more light the plant makes

more sugars. This larger reservoir of sugars

eventually results in the plant making more

side shoots and more flowers. Setting is also

better.

Text: Ep Heuvelink, Tom Dueck, Filip van Noort (all at Wageningen UR) and Tijs KierkelsImages: Jan van Staalduinen and Philips

Plant can use a lot of light

Production very closely linked to amount of intercepted light

Much research has been carried out in recent

years on diffuse light and the results all point

in the same direction: Diffuse light is better

than direct light; yield increases.

Figure. The photo response curve

Light is used more efficiently if the leaves share the available light, such as under diffuse glass.

Light intensity (in µmol PAR/m2/s)

Net p

hoto

synt

hesis

(in

µmol

/m2 /s

)LIGHTFEATURE

34-35-Thema8_IG-Achtergrond-basis1.indd 1 28-09-15 09:42

Light is responsible for photo-

synthesis, fluorescence and warming.

Too much light can cause damage.

However, pot plants appear to be

able to withstand more light than

is commonly used in practise. A

combination of top and interlighting

can be very efficient. Diffuse light is

almost always better.


The way in which we provide light in the

greenhouse can still be done much more

efficiently. Usually the lighting fixtures hang

above the crop. In this way we supply

additional lighting mostly to the upper

leaves, which already get plenty of sunlight.

During the day they quickly reach a situation

when they have too much light. They can’t do

anything with the extra amount and become

too warm. In addition a relatively large

amount of light is bounced back off the crop

by reflection, even at the right light levels.

Trials that combined top lighting with

interlighting show that this system of lighting

does have some prospects. With interlighting

more light clearly lands on the leaf and it

reaches those leaves that are not yet saturated

by sunlight. In addition, the older leaves

remain active for longer, which can have an

important yield-increasing effect.

Diffuse light better than direct Much research has been carried out in recent

years on diffuse light and the results all point

in the same direction: Diffuse light is better

than direct light; yield increases. The reason

is simple: A crop is very dull. It doesn’t like

extreme highs or lows in temperature or light

intensity. This happens regularly in the

greenhouse. For example, when the sun is

very bright and the glass is normal you

always see areas of sunlight and areas of

shadow. The sun flecks disappear under a

diffuse glass or coating. The upper leaves

receive less light, the leaves at the bottom

somewhat more.

Photosynthetic efficiency With respect to plant physiology, the use of

diffuse glass has quite an effect. If the light

intensity is too high it can lead to localised

stress; here photosynthesis severely

deteriorates. But even without extreme stress

the photosynthetic efficiency drops at higher

light intensities. This is shown in the photo

response curve (see figure). It flattens off at

high light intensity.

If you can distribute the light better you

come into the steeper part of the curve

where the efficiency is greater. For example,

if 800 µmol/m2/s of direct light falls onto a

leaf, the photosynthetic rate is 25.5 µmol

CO2/m

2/s. If this amount of light was ‘split’ by

diffuse glass into two parts of 400 µmol/m2/s,

this results in 2 x 17 = 34 CO2/m

2/s. Therefore

the light is used much more efficiently if the

leaves share the available light.

The crop itself also changes due to the

better light distribution. The capacity of a

leaf to assimilate depends on the light

conditions under which it grew up. In this

way you have sun and shade leaves, which

differ in photosynthetic capacity due to

leaf thickness and amount of chlorophyll.

Because more light lands on the middle layer

of leaves under a diffuse roof they behave

more as sun leaves and their photosynthetic

capacity increases.

Dark period Finally, there’s still the question, for how

long should you leave on the assimilation

lights? Many plants need a dark period

otherwise they suffer growth defects. This

has been extensively studied in tomatoes.

Under continuous light the sugars are

insufficiently transported away. Starch grains

accumulate in the leaf and the chlorophyll

becomes damaged. This can be seen in the

leaves; they turn yellow, tough and hard.

Tomatoes require a minimum of six hours

darkness. Development is underway to make

crossings with wild tomatoes that can

withstand continuous lighting.

Roses can endure 24 hours of light but this

does disrupt the stomata. After cutting the

rose, the stomata don’t close properly which

seriously shortens the vase life. Here too a

dark period is necessary.

Summary

The combination of top lighting and interlighting results in higher yields, providing the grower

adjusts the cultivation measures to the situation.

34-35-Thema8_IG-Achtergrond-basis1.indd 2 28-09-15 09:42


By using a double screen tomato grower Gertjan van der Spek hopes to end with gas consumption of 27 m3.

Gertjan van der Spek is the first grower in the Netherlands without supplemen-tary lighting to install two transparent energy screens without any dehumidifi-cation system. This is his next step towards saving energy having already reduced the use of the minimum heating pipe and ventilating above the screen, instead of making gaps in the screen. In this way he hopes to use less than half a cubic metre of gas per kilogram toma-toes.

The idea of a double energy screen in vegeta-

ble production is not new. A growing number

of pepper growers are choosing this option.

“Pepper plants grow less quickly. Therefore the

screens can remain closed for longer. For them

the switch to two screens is not so great,” says

climate specialist Paul Arkesteijn, of screen

manufacturer Ludvig Svensson.

To show that this offers possibilities for

tomato growers too, a demonstration trial has

been running at the Improvement Centre in

Bleiswijk, the Netherlands, over the last year.

The trial compared the results in an area with

two moveable transparent screens with a

control that had a transparent screen with a

fixed anti-condensation film.

The upper screen was a normal Luxous

1347 FR transparent energy screen and under-

neath was a 1347 FR H2NO with anti-conden-

sation activity: This latter screen spreads out

the droplets of condensation. According to

Arkesteijn both transmit 80% light and when

both are closed they transmit just 64% light.

The crops in both greenhouses grew well. The

trial greenhouse saved an extra 4 m3 gas/m2 of

energy.

More savingsGertjan van der Spek, of Solyco, which has two

units in the west of the Netherlands, grows

Roma-tomatoes on 4.3 ha. He belongs to a

group of six nurseries that together form a

horticultural cluster. They have a joint boiler

house that has access to three energy sources:

Waste heat from the ROCA-central; two com-

bined heat and power (CHP) generators; and

a boiler, which serves as back-up if there’s a

break-down in the supply of OCAP-CO2.

“Within the cluster we want to invest in a

heat pump to further cool the flue gases from

the CHPs. The flue gases are currently 45 to

Text and images: Marleen Arkesteijn

DOUBLE SCREENREPORT

Tomato grower Van der Spek makes distinct choices

No lighting, but still two energy screens without dehumidification

36-37-Thema24-OG-Reportage-basis1.indd 1 28-09-15 09:43

Gertjan van der Spek is the first

tomato grower without supplementary

lighting in the Netherlands to use two

transparent energy screens with no

dehumidification system. After a series

of energy saving actions, such as his

first screen, ventilating above the

screen cloth and sparse use of the

minimum pipe, he took the decision to

purchase a second screen system with

movable screen. With this step he aims

to end with gas consumption of 27 m3

and a yield of around 63 kg per m2.


50ºC. By using the heat pump we’d like to

bring that down to 23ºC. We currently use

900 m3 gas per hour with the two CHPs. The

recovered heat is the equivalent of about 130

m3 gas. To be eligible for the subsidy scheme,

Market Introduction Energy Innovations, the

cluster has to save a total of 15 per cent on its

energy use. That requires extra effort from

each nursery,” explains the tomato grower.

This trial took place at the time when Van

der Spek was one of two growers appointed

to the Supervisory Commission at the Impro-

vement Centre. Hence, the reason he followed

the trial with the two transparent screens

with extra interest.

Two energy screens In spring 2014 it was apparent that the trial

was progressing well which enticed Van der

Spek to install a second energy screen under

his existing screen which he did in August

last year. The fact that his first screen was

already eight years old, was becoming porous

and in need of replacement also played a role.

An investment in a second screen system for

the second screen was also required. This was

not a problem even though this option had

not been taken into account in the construc-

tion during the building of the house. “Screen

fitters Alweco found a solution by attaching

the second cloth half way through the trellis.

As security we ensure that the cloths don’t

move at the same time, because most of the

force occurs on the wall during the opening

and closing.”

The grower chose the light transmitting

Luxous 1347 FR, without any anti-condensation

(AC) activity. “The anti-condensation activity is

not required here because we mostly screen at

night.”

1,500 double screening hours The planting date was 1 December 2014. Up

until the end of April he regularly worked

with two energy screens. The grower always

allowed the new screen to close first. Up to

week 20 he had screened for 2,200 hours; his

old screen was used for 1,500 hours.

Compared with last year he used 0.5 m3

more gas during this period over a slightly

longer cultivation. “In terms of energy con-

sumption it’s about the same as last year but

then it was very mild, in contrast to this year.”

When he compares his energy consumption

with that of colleagues then his consumption

is about 2 m3 less than that of growers with a

fixed AC-foil and 5 m3 of gas less than growers

with a single screen.

During the first six weeks he saved hardly

anything compared with the growers with the

fixed AC-foil. “In this period the biggest advan-

tage is that a moveable screen gives you more

flexibility. I already had other advantages

because with a moveable screen you have less

trouble with moisture. Incidentally, we never

chose to have a fixed foil. I always had the

idea that it only became cold when the foil

was removed.”

During the autumn months, from October,

the screening during the trial in Bleiswijk was

even more intensive and it was possible to

save an extra 1 to 2 m3. “During the last few

weeks of the crop, the temperature has to be

high enough to allow the tomatoes to ripen

properly.”

The New ThinkingIn 2014, when the winter was mild, the grower

used 27 m3 gas per m2 and the yield was 63 kg.

In a ‘normal’ year it’s about 32 m3. “Now we

want to achieve these savings with a double

screen and still get a yield of 63 kg,” says the

grower.

Van der Spek has also made huge strides on

his own nursery over the last few years. When

he started in 1992, he used 72 m3 gas. After the

construction of a new greenhouse in 2000

consumption dropped to 50 m3 gas. In 2005 he

installed his first screen and it fell even further

to 40 m3. The step to 32 m3 happened primarily

thanks to new cultivation methods. The pro-

duction increased from 50 kg in 1992 to around

the 63 kg of tomatoes today. “The use of

grafted plants increased production to over

65.5 kg. Now we’ve conceded some yield to

save energy.”

The result is impressive: from 1.5 m3 gas

previously to 0.5 m3 gas per kg tomatoes now.

Arkesteijn attributes these new insights about

cultivation to The New Thinking, an offshoot

of Next Generation Growing. “Before, we used

to open a gap in the screen to release moisture

and the result was a dump of cold air in the

greenhouse. Consequently there were diffe-

rences in the horizontal temperature. The

climate was controlled based on the coldest

places. Now growers keep the screens closed

for longer and the moisture escapes through

the screen itself. The biggest advantage is a

uniform climate. That is not only better for

saving energy, it is also better for product

quality.”

Seldom use of minimum pipe The tomato grower indicates that at first he

only ventilated on the leeward side of the

house, out of the wind. Now, with both

energy screens closed at the same time, he

vents from both sides in order to create good

air movement above the screen to help draw

air through the screen. And now, instead of

opening the vents just a little, he dares to

open them much wider.

Another adjustment is that the grower

only uses the minimum pipe very sparingly.

“We’ve dropped the temperature from 50ºC

to 40ºC and now to 30ºC.”

Arkesteijn: “Previously we used to think

that you have to heat the crop so that it will

continue to transpire. Now what matters is

that the crop transpires sufficiently during

the day. The energy screen closes when the

radiation reaches 80 tot 100 watt. The crop is

activated the next day by the sun that shines

through the very transparent screen.”

Summary

Arkesteijn (r) with Van der Spek: “What matters is that the crop transpires sufficiently during

the day.”

36-37-Thema24-OG-Reportage-basis1.indd 2 28-09-15 09:43

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Shelters for predatory mites As part of the project ‘standing army’ we are looking at

possible ways to improve the establishment of predatory

mites. It is very clear that lack of food is often a problem

in ornamental crops. This can be overcome by providing

extra pollen or other food sources.

However, even in crops where an excess of food is

offered, the predatory mites do not always become well

established. In a trial with pot plants it was found that

the density of predatory mites was ten times higher in

spathiphyllum than in anthurium, even when a similar

amount of pollen was added to both plants. The possi-

ble reason is that when the air humidity is low, spathi-

phyllum offers more shelter as it has a better micro-

climate than anthurium.

On some plants these shelters, so called acarodo-

matia or ‘predatory mite houses’, are very clearly present.

Often they are dense clusters of leaf hairs on the area

where leaf veins come together (see photo). These

domains provide a better microclimate as well as offer

protection against the predators of predatory mites.


WAGENINGEN UR GREENHOUSE HORTICULTURE

For more information please contact: José Frederiks, office managerWageningen UR Greenhouse HorticultureTelephone: +31 317-483878Email: [email protected]

Mushroom compost works against root knot nematodes

Horticultural training for greenhouse systems in Rwanda

Root knot nematodes are a problem in the organic

production of fruit vegetables. A trial is being carried

out in Bleiswijk together with organic growers to test

measures for the propagation and cultivation of

tomatoes.

Five litre pots were filled with soil from the growers.

The research focused on various types of compost,

additives such as silicon as well as antagonists to root

knot nematodes. The measures were tested separately

and in combination with each other to see if it was

possible to achieve a synergetic effect. Woody compost

and mushroom compost with silicon in particular were

able to reduce the number of root nodules on the roots.

Woody compost also resulted in a reduction in the

number of offspring. However, adding the fungus

Trichoderma was counter-productive and reduced the

suppressing effect.

The combination of mushroom compost and silicon

also reduced the number of root nodules. The effect

was stronger when the products were given together

than when each was given separately. Use of mushroom

compost also resulted in a larger (heavier) tomato plant.

Mushroom compost does need to be applied carefully

because the material is ‘sharp’ and can damage the roots.

Together with a number of Dutch companies and

research institutes Wageningen UR Greenhouse

Horticulture is taking part in the SMART-programme.

The project focuses on Africa and has already organised

demonstrations and training for greenhouse cultivation

systems at different levels of technology in Rwanda and

South Africa.

Rwanda is a country with a suitable climate for green-

house production and has a strong, growing interest

in covered cultivation. Together with Rijk Zwaan and

Koppert, training has been organised for managers and

staff of the RwandaBest Company who are preparing for

the first crop in a new greenhouse built by Bosman Van

Zaal and equipped by Hoogendoorn.

Covered cultivation in Rwanda is still at a low level

in terms of technology, cultivation technique, production

and product quality. Issues such as plant care, water and

nutrient supply, crop protection and marketing can still

undergo much improvement. There is, however, a

reasonable demand for good tomatoes in supermarkets

and hotels but these customers expect continuity and

good quality.

Water cultivation of iceberg lettuce in cabrio greenhouse

The production of iceberg lettuce and other types of

lettuce on water cultures in Bleiswijk is progressing

well. Lettuce is growing in two plastic greenhouses on

the Dry Hydroponics system. During the winter LEDs

provide supplementary light during the day.

As the weather turns warm, the roof and sidewalls

of this greenhouse can be fully opened. It is being

investigated whether iceberg lettuce can be grown year

round in a sustainable way and still maintain a good

quality. Certain customers, such as processors,

increasingly require a year round supply of a product

with a consistently high quality.

By increasing the planting density from 20.8 to 25 plants

per m2 (+20%), the weight of the heads of various types

dropped by 10%, but the total number of kilos increased

by 8%.

Compete Plus is added to each container on a

monthly basis. This increased the harvest in February,

March and April by 15, 5 and 0% respectively. Thus the

effect decreased with time. With more artificial light,

together with a higher greenhouse and water tempe-

rature, the lettuce grew faster in winter. The water was

heated to 15 or 17ºC, depending on the light intensity of

the artificial light.

39-Thema21-WUR.indd 1 28-09-15 09:45


Pests such as insects, mites and nemato-des don’t just cause damage, in the case of quarantine pests they can also limit exports. In cooperation with the sector, entomologist Yutong Qiu tested the possibility of using Controlled Atmos-phere Temperature Treatment (CATT) in the post harvest phase to control these pests in a non-chemical way. Within the short term this approach is expected to successfully control Tuta absoluta in tomatoes and thrips in chrysanthemums and peppers.

The ‘controlled atmosphere’ (CA)-technique

is already widely used during the storage of

fruit and vegetables. Heat treatment is another

technique currently used. The CATT-method is

a combination of both, in which the composi-

tion of both air as well as temperature can

vary. By applying an atmosphere that contains

a low level of oxygen and more carbon dioxide

at a slightly raised temperature, the aim is to

kill the pests within a few hours to a few days

while preserving the product.

Standard treatmentThis method was developed for the environ-

mentally friendly disinfection of propagation

material for strawberries against strawberry

mite when disinfection with methyl bromide

was banned. The strawberry mite is control-

led while the plants remain in good condi-

tion. Strawberry growers now use this as a

standard treatment.

Carbon dioxide and oxygen are gases that

are normally present in the air so the CATT-

treatment is regarded as non-chemical and

therefore does not require special permis-

sion. The method is included in the Elite-

certification for strawberry plants. In the

meantime two companies in the Netherlands

are applying this method of disinfection to

the whole sector.

Four parametersThe next step was for researcher Yutong Qiu,

and colleagues at Applied Plant Research (PPO)

in the Netherlands, to see if was possible to

apply this non-chemical approach to quaran-

tine diseases. In one of the projects financed

by the Dutch Ministry for Economic affairs

they screened, in close cooperation with

Wageningen UR Food & Biobased Research,

ten different quarantine pests. The project

ran from 2012 until the beginning of this

year.

Text and images: Marleen Arkesteijn

PLANT HEALTHRESEARCH

CATT shows promise against quarantine pests

Short term non-chemical approach to Tuta absoluta and thrips

Screening for the ideal atmospheric conditions is taking place at Wageningen UR Food & Biobased Research where there is a range of 64 ‘mini’

CATT-setups



The screening took place at Food & Biobased

Research which has a range of 64 ‘mini’ CATT-

set-ups. This makes it possible to test a wide

range of possible conditions parallel to each

other over a short time. This is in contrast to

just the one condition found in commercial

conditions. Qiu varied the temperature, the

air composition (percentage of oxygen and

carbon dioxide) and the time duration.

As an example, she refers to a treatment

lasting between 1 and 24 hours at a tempera-

ture of 35 ºC in an atmosphere containing

50% carbon dioxide and less than 5% oxygen.

“At the moment we are still in the testing

phase. The final treatment conditions are still

being developed,” she says. “The range of

temperature and air composition with which

you can kill pests is wide. The band in which

the plant or product remains good is much

narrower. This can even be different per

cultivar. The combination of these two

should lead to a tailor-made treatment.”

Thrips, spider mite and leafminer As a follow-up to the broader screening

they ran another project that focused on the

most important pests: western flower thrips,

Frankliniella occidentalis; tomato leafminer,

Tuta absoluta; tulip stem nematode, Ditylen-

chus dipsaci; spider mites and nematodes in

potting compost.

Once again the researcher screened these

pests based on the ability of the CATT-method

to kill them in combination with different

products. This project was funded 60% by

Dutch businesses, which included horticultu-

ral trade organisations.

The researcher and her colleagues now

want to take the most promising pest-product

combinations from the lab trials a step further:

They want to scale up the trials in practise at

two controlled atmosphere companies. “These

two CA-companies took part in the trials with

strawberries-mother plants and now have

the technique to disinfect strawberry plants

according to the CATT method.”

She not only wants to test these methods for

thrips on the end product, the flowers, but

also on the propagation material, the cut-

tings.

PossibilitiesQiu expects the first application in about two

years. “The success of the method depends

on the sensitivity of the pest and the product.

A product such as poinsettia is very sensitive

to temperature. Chrysanthemums can take

more. A difference between varieties also

plays a role in the sensitivity of the products.

And the more lively the pest the easier it is to

kill. We look at all stages of the insects. The

last caterpillar stages and the pupa stage are

often the most difficult. A white fly, which

still sits and sucks, is also more difficult to

kill. Pests, such as codling moth, which

burrow in the fruit, are also less simple to

deal with.”

The CATT-method (Controlled Atmos-

phere Temperature Treatment) invol-

ves products being kept for several

hours in a room with a controlled

temperature and air composition

(certain percentage of carbon dioxide

and oxygen). It is important to create

conditions that will kill the pests but

not harm the product. Within a couple

of years researchers hope to have

found the right conditions so that this

method can be used against Tuta

absoluta in tomatoes and thrips in

chrysanthemums and sweet peppers.

Summary

Researcher Yutong Qiu: “A high percentage of carbon dioxide is a good post harvest treatment

against the tomato leafminer, Tuta absoluta.”

Looking at the list, she expects to achieve the

first results with Tuta absoluta in tomatoes

and thrips in peppers and chrysanthemums,

both in the cuttings as well as the end pro-

duct. Not only the method, but also the order

of the logistical process counts. “It’s important

to agree with nurseries where this disinfection

method - that can take several hours - best fits

into their delivery process.”

Certification Parallel to the research, the researcher also

looked at the possibility of developing a

certified protocol. “During the large scale trials

we maintain close contact with the Dutch

Food and Consumer Product Safety Authority.

They can help us work towards an internatio-

nal standard, for example, for the CATT-treat-

ment for tomatoes to kill the small leafminer

Tuta absoluta. This method offers opportuni-

ties for expanding the export market.”

Researcher post-harvest technology, Jan Verschoor, shows how he can adjust the air composition

exactly by using a controlled input of individual gases.



Careful watering is very dependent on the possibilities within the nursery. When things go wrong you may find the last six rounds of watering have accu-mulated in the irrigation hose. That happens just as easily in large or small systems, discovered researcher Chris Blok. You can already take this into account when installing a new irrigation system.

A trial is being carried out in the greenhouses

at Wageningen UR Greenhouse Horticulture

on irrigation systems for sweet peppers. This

research has been set up with water specia-

list, Revaho, and is testing the speed of the

watering systems within closed cultivation

systems. Researcher Chris Blok and product

specialist Stefan Bakker explain why it is so

important to know what happens in the

dripper pipelines and within the drippers

and why it is so difficult to calculate this

well. The period of time that the solution

containing fertilisers or crop protection

substances remains in the pipeline is much

longer than you would expect.

Loss of speedThe time it takes for the water to flow past

the first dripper to the moment it reaches the

last plant is called the ‘travelling time’. Sup-

pliers of irrigation systems have a special

calculation program for this. As long as the

water is still in the main pipeline it is possi-

ble to calculate exactly how long it takes

from the fertiliser unit to the first dripper. Up

to that point the flow rate remains the same.

Once the nutrient solution reaches the

first dripper part of the solution enters the

dripper for the first plants, the rest continues.

Each time a little amount of water leaves the

pipeline as it enters the next dripper the

speed of water flow slows down. And as the

amount of water continually decreases the

time it remains in the pipeline as it approa-

ches the end increases.

This problem doesn’t just happen on nur-

series with long paths, it happens indepen-

dently of the length. However, there is a

relationship between the resistance in the

pipe and the path length but this effect

cannot be calculated.

Six rounds of watering When administering crop protection pro-

ducts, you want the substance to act on the

roots all night long. A contact substance

needs to remain at the roots for as long as

possible. Therefore you supply that in the

last irrigation of the day. A systemic subs-

tance is applied at the start of the day to get a

good take up through the process of transpi-

ration.

Meanwhile Chris Blok has been able to

show that it certainly takes six rounds of

watering before the substance reaches the

last dripper (of standard size). If you supply

the substance in the evening then it doesn’t

take much explanation to realise that the

substance will arrive a day later. Most sub-

stances still work then but the contact period

is much too short because new rounds of

clean water arrive shortly afterwards. If, for

example, you supply 0.25 litres per m2 per

day in the winter, then it can take 17 days

before the last point is reached.

Delay and decomposition Stefan Bakker: “Therefore you need to take

into account that the water flows through

the nursery in waves.” As a result of measure-

ments taken in the greenhouse, a model has

been created which predicts how the water

is distributed.

It’s the same principle when raising or

lowering the EC in greenhouse vegetable

production based on light. Many growers

think that they are having a direct impact but

even in the summer it can take hours before

the correct EC reaches the last point. Add that

to the fact that these plants are less visible,

the grower notices far too late that his treat-

ment makes little sense. Stefan Bakker: “That

is also the reason why we install many sys-

Text and images: Pieternel van Velden

DRIPPERSFEATURE

Specialists advise about sensible watering:

‘ Avoid delay when distributing fertilisers and crop protection agents’

Stefan Bakker (left) and Chris Blok: “As a grower you need to take into account that the water

flows through the nursery in waves.”

Pressure compensating drippers give you more

opportunities to steer the crop.

42-43--Thema5-OG-Achtergrond-basis1.indd 1 28-09-15 09:47

Wageningen UR Greenhouse Horticul-

ture has developed a model to clarify

how water is distributed within the

irrigation pipelines and dripper lines.

Within just one dripper pipe seven

rounds of watering can accumulate.

This results in problems with the

distribution of fertilisers and crop

protection products. By making simple

adjustments you can greatly reduce

this problem.


tems the other way around, so that the last

dripper is by the path and the crop’s response

at the end of the water line is visible.”

SolutionThere are several ways to get around this

phenomenon. Bakker knows that applying

pressure to both ends of the irrigation system

doesn’t work. “Then you only move the pro-

blem. The parts where there is still water from

previous rounds shift towards the middle but

they are still present and the water runs

towards the drainage from both sides but

then half as fast.” Another way is to supply

a substance over several waterings. That at

least takes care of the water accumulation

in the system.

By far the best way is to use pressure-

compensating drippers combined with

rinsing. Using these drippers it’s possible to

flush out water in the system using low

pressure and at the same time put water

and substances in the pipeline under low

pressure and then allow it to drip out under

high pressure.

A good option is to go for a thinner drip-

per pipe so that less water remains behind

in the system. This can be combined with

smaller drippers of, for example, two litres

instead of three. But then you do have to take

into account that a thinner dripper offers

more resistance than a thicker one.

Think carefullyIt’s really not all that complicated if everyone

in the chain recognises the problem. Then

it’s also possible to think of good alternatives.

“For example, it is important to consider

whether you’re on a tanker or a speedboat,”

says Bakker. “On larger nurseries, for example,

we move towards larger watering areas which

make the system faster.”

The real problem lies within a complexity

of factors. The grower needs to know exactly

how a water system works and the installer

needs to respond to his wishes and be able to

calculate this. In practise the watering system

is installed when a new building is being con-

structed at a moment when a lot is happening

on the nursery simultaneously. Bakker quite

frequently comes across situations in which

the pipework has been installed just slightly

differently to what would have been optimal.

This can lead to a large delay in the system.

Sometimes growers have to economise

on the system layout. Bearing in mind that it

will take five to seven years before another

new system is purchased it is certainly worth

taking time to think about such a substantial

part of the total production system.

Summary

Strawberry growers successfully work with two systems: an in-line dripper hose and another hose with drippers.

Research shows that it takes at least six rounds of watering before a crop protection product

reaches the last dripper.

Figure. Building model: 6 rounds of watering

42-43--Thema5-OG-Achtergrond-basis1.indd 2 28-09-15 09:47


André van Paassen (right) with Tom Zwijsen (left) and Arie Verloop: “You’re rid of all the thrips that you catch early by sweeping and so you don’t

need to spray them.”

The Dutch nursery Arcadia Chrysanthe-mum, of Kwintsheul, has been working with the so-called ThripsSweeper since September. It is a suitable and effective solution with which to catch adult thrips in a chrysanthemum crop. The idea for this innovative device arose during a brain storming session with growers and it was further developed together with them.

Thrips is the biggest problem in chrysanthe-

mum cultivation. The thrips’ pupae and larvae

can be controlled with natural predators such

as nematodes and predatory mites. Adult thrips,

which can transfer viruses and damage flowers

by pricking them, cannot be well controlled

due to the lack of substances available. Many

growers use mass trapping – a sticky trap for

every ten square metres – in order to get rid

of them. This method works well but doesn’t

catch all the adult thrips because the traps are

stationary. To catch even more thrips, the idea

arose to automatically shake them out of the

crop and simultaneously move the sticky traps.

Crop in motion“The idea, that was thought up on a Friday

afternoon, was developed into a device that

moves the crop. As a result the thrips jump

out and are easier to catch. Simple, but effec-

tive,” says Tom Zwijsen, manager cut flowers,

of Horticoop.

The supplier’s technical department

developed a construction that can be moun-

ted under an existing spray boom. Rows of

sticky traps and rubber tubes hang from the

aluminium frame. The tubes are weighted

so that they hang straight down and produce

a tapping effect within the crop. When the

tubes move through the crop they shake the

thrips, as it were, awake. With a fright they fly

up and hit the sticky traps that are following.

The colour of the sticky trap, yellow or blue,

is less important because it’s the shock that’s

effective. The traps do need to be replaced

after four weeks.

Optimal catch results Different types of tubes have been tested in

the chrysanthemums. If the material is too

stiff, it can damage the crop. A flexible tube is

best, so that it also doesn’t get caught behind

the supporting gauze. The tubes that go

through the crop are longer than the sticky

traps; the sticky traps need to remain above

the crop and not touch it. The settings for this


INNOVATIONREPORT

André van Paassen, chrysanthemum nursery Arcadia:

‘ Innovative device is extra tool in fight against adult thrips’


Thrips is a year-round problem. Adult

thrips, which are almost impossible

to control, can be trapped in an inno-

vative device. This uses flexible tubes

to set the crop in motion, which results

in the adult thrips jumping out of the

crop and being caught by sticky traps.

The results are better in a young

crop than in a fully-grown crop.

Because the device can reach the

entire crop the thrips population can

be better kept under control. And

everything that a grower can catch

means he doesn’t have to spray.


need to take into account the slope of the

greenhouse.

It was decided to bundle the tubes

together in threes along the row. André van

Paassen, manager of Arcadia, explains: “The

three tubes make a sort of circular motion

around the plant. As a result not only is the

main stem set in motion but also the side

shoots and leaves. This produces the optimal

catch results.”

Custom-made The first model had two rows of tubes with

a single row of sticky traps in between. Two

additional rows have been added because the

thrips also need to be caught at the back of

the bay by the wall. “Also, if the thrips are

‘swept’ out of the crop we want a sticky trap

behind to catch these too,” says the manager.

He would like to cover the top of the frame

with traps for an even better result.

Zwijsen: “We look at the situation in each

nursery and make the frame to size. Here the

bays are 9.60 m wide and so the frame with

sticky traps weighs 70 kilos. But, you cannot

continue to indefinitely increase the weight

that is hanging from the spray boom.”

Young cropThe first trial runs were carried out in a fully-

grown crop, in which the buds were starting

to show colour. Van Paassen: “We did trap

thrips but not in any great number. Then we

started to ‘sweep’ in a young crop. Here we

caught more thrips because they hardly had

the chance to fall to the ground. The yield is

therefore greater. You’re rid of all the thrips

that you catch early and so you don’t need to

spray them.”

In the 10-week crop the chrysanthemum

nursery uses the device up until the crop is

55cm tall. That is about half way through the

cultivation period. It isn’t used during the first

two weeks because the plant needs to become

securely rooted. The mechanical treatment

takes place in week 3, 4 and 5. From week 6 the

crop is in bud and they start to open. The

removal of the thrips is an advantage for the

biological control which is released in week 3.

Dismountable frameThe innovative device can be disconnected

from the spray boom. The manager uses the

latter in the evening and early in the morning

for corrective spraying against thrips larvae.

The sweeping takes place during the day

when the adult thrips are active. Ten bays are

treated each day.

The device travels five consecutive times

through the same bay. After the second run

there still aren’t many thrips on the sticky

traps. There are many more after the third

time but it’s only after the four and fifth run

that the amount is the greatest. “Thrips live

on the underside of the leaf and in the

growth points. After been shaken a few times

they want to move,” says Van Paassen.

At the site in De Lier the intention is to

spray as well as use the new tool in order to

reach the underside of the leaf better. The

tubes turn over the leaf as they move through

the crop.

Positive expectationVan Paassen hopes that by removing the

thrips there will be less disease pressure

during this spring and through the better

biological balance the disease pressure will

remain low. That could result in less spraying

during the summer and a better quality pro-

duct.

“During the winter period, when due to

the lower temperature the thrips are less

active, we trap very few thrips. Still it’s good

to do it because with the artificial lighting the

thrips population continues to rise. And you

don’t know how many thrips are lurking at

the back of the bay, that could develop into a

local population. If the temperature rises in

March and April and the sunlight increases

you could be in for a surprise. Now we expect

thrips to be less of a problem,” says the

manager.

This device gives him a better picture of the

thrips population in the nursery. If necessary

he can react faster to the problem. He has not

seen any damage within the flowering crop or

growth inhibition as a result of the device. “The

quality of the flower stems is still good,” says

Van Paassen.

Summary

The tubes that move through the crop turn

over the leaves.

The black tubes are longer than the sticky

traps as the latter do need to remain above

the crop.

The ThripsSweeper goes back and forth five times over the same bay. The fourth and fifth times

trap the largest number of thrips.



The grower who wants to provide his substrate-based crop with precisely the right nutrients will be better off forget-ting the nutritional formulas. If you want to do it better you should from now base it on analysis of uptake by the plant. This is much more accurate. The potential gains from this method will grab most growers’ attention: Better control over vegetative and generative growth, efficient use of fertilisers and more kilograms.

Analysis of plant uptake is at best considered

a hefty calculation involving a number of

factors. These are the mains water and its

composition, the drain water and its compo-

sition, the measured amount of water uptake,

the measured CO2 level, the volume of drain

water and the radiation. When the sum has

been properly worked out then you know on

one hand which nutrients have been taken

up by the fruit and on the other hand by the

plant’s green material. The calculation can be

worked out for every element.

Well-known pitfallThe inventor of the system is Ruud Kaarsema-

ker, project leader at Groen Agro Control,

Delfgauw, the Netherlands. Meanwhile

around 60 nurseries are using this systematic

method. It was created as a result of questi-

ons posed by commercial growers. “It was

already known that cultivating based on a

nutritional formula was not always very

accurate. By accuracy we mean: The plant

receives what it needs. Growers started to

ask themselves if something could be done

about the inaccuracies.”

He gives the following example: “Research

with peppers has shown that a high level of

the element boron in the slab doesn’t always

equate with sufficient boron in the plant.

When considering the slab you’d assume that

too much boron has been supplied. You’d be

tempted to reduce the dosage, something that

often happens in practise. But because the

plant has a shortage and apparently has taken

up too little, you should at least continue

with the high dose. This example illustrates

the well-known pitfall: what the slab tells

us is not automatically the reality in the

plant.”

Five factorsWith help from uptake analysis the nutrients

can be supplied much more accurately. Accu-

racy is based on a number of factors. Kaarse-

maker has made a list:

1. The uptake by the crop responds mostly to

concentrations in the irrigation water. If

the composition of this changes the uptake

by the crop changes almost automatically.

2. The concentration in the slab is mainly the

result of what the crop has taken up. If the

concentration in the slab remains high

then the plant has taken up very little. If

the concentration is low then in general

the plant has taken up a lot.

3. The difference between the dose and the

uptake often provides a better picture of

the nutritional status than the concentra-

tion in the slab.

4. Anyone who adjusts the nutrients based on

the concentration in the slab is driving the

plant in completely the wrong direction.

The nutrients are corrected the wrong way.

The example mentioned previously with

peppers and boron makes this very clear.

5. By adjusting the nutrition based on an

analysis of the uptake, the dose is much

more accurate and swings in the nutrient

solution are much smaller.

Steer vegetatively or generatively?Analysis of uptake can bring advantages to

many nurseries. One important positive

point is that the grower is able to better steer

the crop towards vegetative or generative

production. He can achieve this using the

ratio between sulphate and chlorine with

nitrate. Early on in the cultivation he has to

supply relatively more sulphate and chlorine

than at the end of the production to realise

the same amount of generative growth.

“If the grower wants to know exactly how

much of each element he needs to supply,

there’s more chance of him achieving this

with uptake analysis than with a traditional

nutritional formula. Every grower asks himself

how he can bring his crop into just the right

Text and images: Jos Bezemer

ANALYSIS OF UPTAKEFEATURE

Analysis of crop uptake replaces traditional nutritional formula

What the slab says is not automatically the opinion of the plant

Ruud Kaarsemaker in the research greenhouse: “The largest gain is the potential extra yield.”

46-47-Thema6-OG-Achtergrond-basis1.indd 1 28-09-15 10:08

By using a calculation model it’s

possible to determine the amount of

nutrients taken up by a plant from a

substrate. The uptake analysis makes it

possible to steer the fertilisation much

more accurately compared with the

traditional nutritional formulation. The

advantages are many: greater ability to

steer crop growth, higher yield in kilo-

grams, more efficient use of fertilisers

and less risk of making errors so

that, for example, resilience is not

threatened.


balance; to what extent should it be vegeta-

tive, to what extent generative and what

reserves does he want at the top? This analysis

allows him to steer these three things more

accurately bringing higher yields within

reach.”

Lower input of fertilisers Kaarsemaker expects that thanks to this new

method of analysis commercial growers will

use fertilisers more efficiently. Then for exam-

ple, the grower can prevent the plant making

too much leaf material. And producing less

leaf surface area automatically means a lower

requirement of fertilisers.

Correction is possible as well: “Not only

is it possible to achieve the required plant

balance, a crop that has become too lush can

be thinned down and made more generative

by properly adjusting the ratio between

sulphate and nitrate. That is not possible

with a fixed nutritional formula.”

For that matter, the project leader believes

that the biggest advantage is not the higher

efficiency. He says it’s more about better fruit

quality and more kilograms as these deter-

mine the profit. So how many extra kilo-

grams are possible? “If you take the two cases

widest apart – the grower who fertilisers very

accurately and his colleague who does it

more by guesswork – then the difference

could be an extra five kilograms per square

metre.”

Shorter learning curveThere are other advantages. You can forget

the rule of thumb that it usually costs a

grower a couple of years to be able to ‘read’ a

new variety, or in other words to be able to

master the nutrition and steer the growth.

Kaarsemaker: “Now, with help from the

uptake analysis, a grower can see much more

quickly what the crop is doing compared

with the norm or compared with the grower’s

chosen target. The learning curve is shorter

and the chance of errors is less. That makes a

difference to the cost of learning.”

This method also has a lot of potential

with respect to the crop’s resilience. The

resilience above and below the ground is

mostly dependent on the elements nitrogen,

magnesium and calcium. “Less nitrate, for

example, makes the plant less sensitive to

diseases but too little leads to problems; too

little uptake of nitrate reduces photosynthe-

sis and the plant becomes weaker. It’s the

same for magnesium and calcium: when there

is a shortage, sensitivity to fungal diseases is

greater. By analysing the uptake, the grower

can adjust the given amount if required

without the plant suffering any harm. Because

it’s easier to determine the lower limit, you

can keep it in sight.”

The project leader expects that steering

based on uptake analysis will in a few years

time be widely used.

Summary

By doing an uptake analysis a grower can eliminate the classic pitfall: What’s in the slab is not necessarily the same as what’s in the plant or

what the crop needs.

46-47-Thema6-OG-Achtergrond-basis1.indd 2 28-09-15 10:08

Dirk Aleven: “In Georgia we are growing batavia, lollo rosso, lollo bionda, romano, salanova and rucola with an average head weight of 130 gram.”

48

Dutch entrepreneur Dirk Aleven lives in Georgia. His company has a glasshouse of 6,000 m2 in which 3,600 m2 are used to grow lettuce. “Our greenhouse is comparatively small but we grow lettuce on water. Then it’s a lot. With an annual turnover of 1 million heads of 130 gram each we can supply the entire country with lettuce.”

The company FoodVentures has set itself up

in countries such as Georgia and produces for

the local market. Entrepreneur Dirk Aleven

explains: “There is a large demand for quality

vegetables in this country. The young gene-

ration is no longer interested in farming and

is migrating towards the towns. In the super-

markets they want to be able to buy all sort of

vegetables all the time.”

Vegetables are mostly grown in the open

field so local producers are dependent on the

weather. During the months of April, May and

June they grow plenty of vegetables and for a

few months they are in abundant supply. Du-

ring the other months there is a large shortage

of fresh vegetables. To overcome the shortage,

the country imports a lot from Turkey and

Iran. However, the quality of these vegetables

is poor. Aleven saw an opportunity: “Georgia is

a small market, but one that demands quality.”

A few years ago he didn’t expect to be

living here now with his family. “I started a

world tour on my motor bike travelling from

the Netherlands to Nepal. In Georgia I got tal-

king to some local businessmen about green-

houses.” At that point his company had no

plans to build in Georgia but it was already

in the process of building a greenhouse in

nearby Ukraine.

Garnish for dishes“In Ukraine we had many economical and

political set-backs. As a result the nursery

opened in 2015 instead of the planned 2013,”

explains Aleven. “By comparison, in Georgia

the construction went very fast. We started in

June last year and opened in December. At the

moment we are ahead of schedule.” But in

Georgia things aren’t easy either. The inhabi-

tants know lettuce but mostly as a garnish to

dishes. It is hardly ever a main part of the

meal. Therefore the market still has to be

developed. It’s a question of promotion and

waiting.

Nevertheless, the entrepreneur is positive.

“We are just starting. Our strength lies in the

continuous quality we offer. We sell high-

quality lettuce which appeals to the restau-

rants.” With a turnover of one million heads

per year the company can supply the entire

country with lettuce. The lettuce varieties,

batavia, lollo rosso, lollo bionda, romano,

salanova and rucola with an average weight

of 130 gram, are grown in an area of 3,600 m2.

“We now have sales of 1.5 tons per week. The

maximum that we can achieve from this

Dutch teach local producers how to produce more effectively

‘ I want to help growers, I don’t need to own the largest greenhouse in Georgia’


GEORGIA REPORT

Text and images: Janita Elings


The Dutch company FoodVentures has,

since last December, a greenhouse in

Georgia that is producing lettuce on

3,600 m2. According to entrepreneur

Dirk Aleven, the current processing

area of 2,400 m2 is proportionally too

large and therefore the nursery wants

to expand this year. A greenhouse of 1

to 1.5 ha will be built for the produc-

tion of aubergines and cucumbers. The

company also provides other nurseries

in the area with cultivation advice that,

according to Aleven, is desperately

needed.

49

greenhouse is about 3.5 tons per week.” But at

the moment the company is purposefully not

maximising production until the market picks

up further.

Unskilled producersGreenhouses at other nurseries in the country

tend to be of low to mid quality. Aleven has

noticed that a company often builds a green-

house in order to earn a little extra from its

waste heat. He’s amazed at what he encoun-

ters in the greenhouses. “I come across the

craziest things, such as a tomato greenhouse

with a yield of only two kg per square metre.”

According to him it’s because producers don’t

share information with each other and be-

cause they are not educated in horticulture

and modern cultivation techniques. “It makes

sense that the plants don’t perform.”

His nursery employs 30 people including

a Dutch head grower, Dick de Jong. The glass-

house was built by Kubo; Dry Hydroponics

installed the cultivation system. The green-

house is heated with geothermal energy and

that is also the reason why the nursery is

located in Samtredia. “A heat source dating

back to the Soviet era heats our greenhouse,”

says Aleven. “The cost price of a lettuce is for

twenty to thirty per cent determined by the

heating costs and that is for us free of charge.

We only have to pay for the CO2. But that is

relatively expensive, so after the next expan-

sion we will probably also use some gas for

heating.”

LED-lightingThe LED-lighting from Philips was a large

investment. “It was a simple decision. Due

to the low light conditions we need to use

supplementary lighting during the winter

months but we didn’t want any additional

heat, because lettuce has a hard time when

the temperature is high.” Samtredia does

experience warm winters. “You want to build

something that you believe in. Thanks to the

LEDs I have supplementary lighting without

the extra heat. Therefore, I can say with

certainty that we will continue to supply a

stable quality over the next ten years.” The

vegetables are lit for 15 hours per day in the

winter months. “At the moment that is enough

but if the market expands then we will proba-

bly increase the number of hours when we

use lighting.”

Aleven says that the price for the products

in Georgia is fundamentally higher than in

the Netherlands. “We receive on average € 1.10

for a kilo lettuce, although we have to do a lot

more for it. There’s no Greenery or wholesaler

here to whom we can sell everything. We have

to find the customers ourselves.” The company

has a processing area of 2,400 m2 and in the

future will also handle products from the

region.

Boost local production “I don’t need to own the largest greenhouse in

Georgia. With my greenhouse I want to show

the local producers how they can produce

more effectively.” That is desperately needed,

stresses Aleven. “The market consists of small,

independent suppliers with no experience or

knowledge. They don’t have any guidelines,

no figures about light, nothing. They don’t

know how to measure the pH and EC and

they muddle along with irrigation and pest

and disease control.”

The entrepreneur wants to introduce

the Dutch model - by sharing knowledge -

to the Georgian producers. He has already

successfully given cultivation advise to one

nursery. In exchange for a share of the profit,

he ensures that the production increases as

much as possible. In a plastic greenhouse for

cucumbers the yield has increased from 8 kg/

m2 to at least 26 kg/m2. “Due to the limited

resources this was a good result but with a

better greenhouse a lot more would have

been possible.” His company is shortly to

advise a second nursery.

ExpansionAleven has more plans for the future. As well

as processing products for the region he

wants to expand his own production facili-

ties. In 2015 he will start building on a site of

1 to 1.5 ha for aubergines and cucumbers. In

addition, the entrepreneur wants to increase

the sales market. “I also want to export to

Russia because there the demand for quality

vegetables is even greater than in Georgia.”

But that is not on the agenda for this year.

“I only want to do that when we have achieved

a good constant market in this country. I don’t

want to be dependent on exports, especially

bearing in mind the unstable trade relation-

ship between Georgia and Russia.”

Summary

Production of lettuce takes place on water.

A geothermal heat source from the Soviet era

heats the greenhouse.



growing solutions

Save on water and fertilizers by recirculating drain waterHortiMaX has launched the latest development in water disinfection with low pressure UV technology. Our new HortiMaX VitaLite E-series allows you to reuse your drain water safely and reliably without adding chemicals.

Save on water and fertilizersReusing your drain water will not only benefit the environment, but will also save you money. Depending on your individual needs, our VitaLite disinfection unit will provide a full return on investment within 2 to 3 years. Call us now, so we can calculate your ROI.

No chemicals addedWater disinfection using UV radiation is the safest technology available today. You don’t need to add chemicals to your drain water, which can accumulate in your recirculation system. This means no chemicals can be passed on to your crops, making it safer for your plants.

Reliable, safe and controlledOur VitaLite unit is equipped with sensors that continuously monitor the water flow rate and applied UV levels. The HortiMaX controller ensures that your drain water is treated with the most effective UV dosage and efficiently manages the water flow between your drain water tanks.

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PRODUCTNEWS

Ebb & Flow bench trays up to 1720 x 6200 mm

The Danish Stål & Plast has been manufacturing Ebb & Flow bench trays in high impact polystyrene since 1984. Recently the company has expanded its product range with larger dimensions. Today they offers these trays in all sizes up to 1720 x 6200 mm. Uniformity, high quality and short, reliable delivery times are keywords for these products.

Over the years, the bench trays have been thoroughly tested for use with fertilizers, effects of temperature change, UV radiation and general daily wear in a modern greenhouse. This knowledge is used for continuous improvement and to optimize the products, so that today they represent the industry is absolute best quality.

The bench trays are manufactured on modern automatic vacuum forming machines. The production facilities are operated mainly by robots which are supervised by specially trained personnel with many years of experience.

Today the comprehensive bench tray system is sold through a worldwide network of distributors. Distributors are typically greenhouse construction companies who install the trays as part of a turnkey projects as purchased by nurseries.More info: www.staal-plast.dk

Clip prevents tearing of topped tomato plants

Tomato plants that have been topped run the risk of tearing in the axil. As the growing stems become heavier the plant is vulnerable to splitting. It can amount to hundreds of plants per hectare with axil damage, resulting in unnecessary growth inhibition

A solution is the Twinhook, a ‘double clip’ made from plastic which provides the axil with exactly the support it needs to prevent damage. According to supplier Royal Brinkman the clip can be attached very quickly and easily due to its clever design. It is recommended to attach the clip within one month after planting.

Growers have been searching for solutions to prevent tearing for a long time. Many have tried providing the plant with more support by twisting two clips together. However, this is laborious and labour intensive. The need for additional support depends on the variety; some varieties always produce heavier plants or are weaker by nature and tear more readily. It also appears that crops with supplementary lighting are more likely to tear. More info: www.brinkman.com

Concept for self-build conveyor systemsTrexx Modular Conve-yors is a patented new system that allows users to quickly and easily build a conveyer system themselves. The concept has been developed by Jonge Poerink Conve-yors, specialists in conveyor systems.

The design is based on a modular building prin-ciple with lightweight parts made from polyethylene. In addition, an assortment of compatible components is available. Thanks to the modular approach it is flexible and offers unlimited expansion possibilities. The installation, customisation and dismantling require no special skills, tools or assembling.

The construction parts can be made to any length and are available in straight or curved versions. This makes it possible to create bends and thereby best utilise the available space. More info: www.trexx.com

Solution for preventing iron deficiencySupplier Van Iperen has launched Fervent Duathlon, a new product against iron deficiency. It has a unique composition and is suitable for open field, pot and substrate crops.

According to product manager Gert-Jan Dillo of The Dutch company in Westmaas, it’s the special composition of the pro-duct that makes it effec-

tive. “The unique combination of EDDHA- and HBED-chelates makes it a particularly effective product. The EDDHA-chelates provide fast initial activity for the plant. In addition, the HBED-chelates ensure long-term availability in the root environ-ment.”

The product offers several other advantages. The iron is easily taken up even at a high pH. In addition, the new product is completely soluble and leaves behind only a minimum residue in the fertiliser container. Van Iperen says this introduction is a new solution for combating iron deficiency. The product is available in 5 kg bags.More info: www.iperen.com

New propagation block gives plant more body

Tomato growers who use the new Rootmaxx-propagation blocks from Cultilene are positive about their experiences. Kees Stijger, of Honse-lersdijk, the Netherlands, switched over comple-tely to the new blocks in one go. The fact that the

roots are contained in the block particularly appealed to him. “Roots on the underneath of the block are simply lost. The block is fully developed with roots, with more roots than in other blocks, but less on the underside of the block. You don’t want them there. I am very pleased with what I have seen so far.”

Rick van Vliet of CombiVliet, Maasdijk, says his trial with the blocks was also successful. “During the trial we quickly saw what we wanted to see and we know what can be achieved. A plant with more body.” According to Saint-Gobain Cultilene, these are the strongest blocks with the roots remaining within the block and not on the underside. More info: www.cultilene.com

The news items on this page are provided by suppliers. The editors are not responsible for the content.

First Agrobío bumblebee hives supplied in Turkey

Recently the first bumblebees, produced at the new Agrobío production facility in Antalya (Turkey) were supplied to various tomato growers in the

region. The opening of this new production facility gives growers in Turkey a quicker access to bumble-bees and beneficials. The Spanish company is partly owned by Royal Brinkman.

Bumblebee hives of Agrobío are known as highly active pollinators. The company breeds two types of Bombus terrestris (the large earth bumblebee); a regular and a special summer hive, suitable for use in both glass and plastic greenhouses. An extra ventilation system in the summer version makes them suitable for high-temperature conditions. They also provides solutions based on the use of bumblebees in outdoor crops. Those hives are protected against climate influences by a special insulated package.More info: www.brinkman.com

Compact version of double-lipped truss clamp

In the 1990s Van der Valk introduced the stainless steel truss clamp. Several years ago the company introduced a new, improved version and

demand has dramatically increased recently. This is because this model has a double lip that provides better support for the polyester cables. Thanks to its compact design, less material is needed, so there was no need to increase the price.

The two rounded lips on the clamp prevent the polyester cables from becoming damaged. Truss clamps with one lip carry the risk that, if the lip is inadvertently bent, the polyester cable will be damaged. The truss clamp with a double lip is just 26 mm wide so is very compact. It is available in different sizes, to suit different systems. More info: www.valksystems.nl

Magnesium important building blockThe nutritional element magnesium (Mg) is an important building block for the growth and flowering of plants but it is also a very impor-tant mineral for the health of people and animals. According to

Jaap Brink, of Brink Business, agent for potassium and magnesium producer K+S KALI GmbH, the essential role of magnesium in fertilisation is often underestimated.

Magnesium plays none or hardly any part in the fertilisation recipes yet the element makes a decisive contribution to yield and quality improvement of a crop. Magnesium is essential for many functions, not only for the production of chlorophyll. A deficiency of magnesium doesn’t only occur if the magnesium level in the soil is low. Dry periods and an unbalan-ced fertilisation strategy also can cause magnesium deficiency in crops. A grower doesn’t always realise that, says Brink.

Not only magnesium, but also elements such as sulphur, boron, manganese and zinc deserve more attention with respect to fertilisation. Products in the company’s EPSO-line comply fully with this requirement. More info: www.brinkbusiness.nl

News

51-Thema23_productnieuws-nr4-2015.indd 1 28-09-15 10:14

HandHeld

Makes precision irrigation possible

Gro Sens HandHeld

The GroSens HandHeld allows you to measure the water content, EC and temperature levels

in your stone wool substrate accurately and easily. The multi-measurement facility provides

a representative impression of your entire greenhouse in an instant. The GroSens HandHeld

also features a logging function which can register measured values over a certain period.

The HandHeld can be easily scaled-up to a MultiSensor system. GroSens makes Precision

Irrigation possible.

More information about GroSens can be found at www.grodan.com/grosens

www.precisiongrowing.com

www.linkedin.com/company/grodan

www.twitter.com/grodan

GRODAN151679 Adv GroSens HandHeld 240x340 EN Tekst.indd 1 24-09-15 10:24IG4-Oktober2016-ADV.indd 9 28-09-15 10:25

in greenhouses€¦ · jojanneke rodenburg harry stijger pieternel van velden editor helen...

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