NewsletterGei jkt N i e u w s

All it takes for environmental research

11Eijkelkamp Agrisearch EquipmentMarch 2003

Included in this number:• Interview DLV• De Water Cycle• The ‘Heath forest’ enigma• Soil moisture sensors• Grassmeter• Divernews

Theme: Soil moisture

INTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEW

INTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEWINTERVIEW

2GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com

www.eijkelkamp.com

Arboriculturalists need to keep upwith the latest developments in orderto be able to work with maximumefficiency and grow good products.Arboriculturalists are alsoencountering ever more complexlegislation and environmentalregulations. Remaining well informedand making the right decisions at theright time involves greatresponsibility. DLV Adviesgroep canprovide assistance in this area. Theconsultants of the Tree Nurserymarket group are able to providearboriculturalists expert, objectiveadvice tailored to individual needs.DLV Boomteelt can assist and guidegrowers of ornamental shrubs,conifers, roadside trees, roses, plants,forest and hedge shrubs forpermanent and public gardens.

BABThe Tree Nursery IrrigationConsultancy System (BAB) is thefavoured system for providing treenursery trees and shrubs with theperfect amount of water at theperfect time. A simple method allowsthe grower to test the moisture inthe soil by himself. Based on the typeof soil he determines the amount ofwater that needs to be given.

How doe the BAB actually work?The BAB system works in a verysimple way. The measuring system isbased on determining the soil watersuction power (suction tension). Thesoil water suction power is the valuethat indicates how hard the plantneeds to suck from the soil to beable to absorb water. This suctiontension is measured with the use ofa read-out device (Watermark). Thismeter is connected to four (or more)soil moisture sensors set into theground (Watermarks). This makes itpossible to read the soil watersuction power any time of the day ina simple manner.

Francois van Abeelen: “As part ofthe (financed) ‘Tree Nursery WaterConservation’ project 10 companiesparticipated who represented each ofthe ‘outdoor’ crop groups (roses,

roadside trees, conifers, forest andhedge plants). For a period of threeyears the critical soil water suctionpower was measured with the use ofthe Watermarks from Eijkelkamp.DLV selected the Watermarks as itinvolved a project extending over anumber of years and these deviceswere able to remain in the soilthroughout the winter, since theWatermarks are particularly well-suited to withstanding frost. The

In 1999 DLV Boomteelt, part of the DLV Adviesgroep (DLVConsultants), commenced aproject that aims to promotemore conservative use of wateramong growers. Next follows aninterview with Francois vanAbeelen, Consultant for Nurserybusinesses with DLV Boomteelt.Francois was closely involvedwith the BAB project (TreeNursery Irrigation ConsultancySystem), during which thepurchasing of a large number ofWatermarks became the firstcontact with EijkelkampAgrisearch Equipment.

DLV AdviesgroepDLV Adviesgroep NV is a leading full-service consultancy agency with amain focus on the agrarian market,entrepreneurs in agribusiness, green

space and international markets. Thearboricultural section is respondingto the ever stricter requirementsmade with regard to the quality ofTree Nursery products.

DLV Tree Nursery Irrigation Consultancy

15 cm20 cm PrecipitionWatering

Soil moisture content, watering and precipitation of B2 Sandy soil

70

60

50

40

30

20

10

0

35

30

25

20

15

10

5

0

Soil

mo

istu

re in

cm

Wat

erin

g p

reci

pit

ion

in m

m

18th

Apr

il

21st

April

28th

Apr

il

18th

May

20th

May

28th

May

1st J

une

8th

June

10th

June

18th

June

24th

June

1st J

uly

7th

July

11th

July

20th

July

27th

July

PRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWS

while at the same time thedifferences in yield from a field canbe also be investigated.

Applications:• Yield estimates to establish the

best possible time for mowing or grazing

• Yield estimates for fertilising recommendations

• Grazing test for grassland research

• Precision farming for which it isnecessary to determine thevariation in grass yield from afield (this often involves the useof a geographic informationsystem)

• Information

3

11Grass heightmeter

A useful tool for estimating theamount of grass on a piece ofland is the grass level meter.This meter is thereforeespecially suitable for farmerswho wish to manage theirgrassland in the best possibleway. At the same time themeter is a tool frequently usedin research and for providinginformation.

Environment and cost factorsIt is important for good grasslandmanagement that mowing iscarried out and that cattle is shiftedat exactly the right time. When thegrass quantity is excessive on aparticular piece of land,unnecessarily high losses can occurif cattle are allowed to graze there.If too much length is cut, thequality of the sward could beadversely affected while regrowthwill often be poor. In additionfertilisation recommendations areoften based on the degree of thenext cutting. Grazing or mowingeither too early or too late canoften mean that unnecessaryamounts of yield are lost or thatuptake of the fertiliser that hasbeen applied is unnecessarily late.Keeping in mind the environmentaland cost factors, knowledge of theexpected dry feed yield is thereforeof considerable importance.

Fast and no mowing requiredThe NMI grass meter available fromEijkelkamp Agrisearch Equipment isa simple, non-destructive methodfor measuring grass height in aparticular field. It allowsmeasurements to be taken speedilyand in relatively many placeswithout the grass needing to bemown. In this way an averagegrass height can be established

entire measuring system is durable,in fact. The project has by now beencompleted but DLV is continuing thework by itself. It will become moreand more worthwhile to participatein the application of a waterconservation system such as this. Forgrowers in the province of Brabant(NL), for instance, it means that ifthey apply this water conservationsystem, they will receive a refund oftheir provincial groundwater taxlevy!”

Taking measurements“The principle is as follows: For thegrowers it is important that theymeasure the suction tension of thesoil twice a week and that they faxthe data through to DLV Boomteeltin Boxtel. In addition the growerneeds to pass on the naturalprecipitation and the irrigationamounts. Once the data have beenprocessed, it is therefore possible, atthe end of the growing season, tocreate a clear overview of themeasured values. This in turn allowsuseful conclusions to be drawnconcerning the irrigation process.Matters such as ways to improve thewatering regime as well as improvedgrowth are some of the benefitsexperienced by the grower.

Additional growth spurtsIn Boskoop (NL) BAB helped toinvestigate how 5 buxus (box)growers could ensure additionalgrowth spurts* in the plants so thatthey would grow bigger. It was asuccessful effort, and the growersconcerned are more than happy withthe results”, Van Abeelen tells us.

*) Normally buxus (box) undergoes two growthspurts per year.

y System

4GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com

New in the ‘Geijkt Nieuws’ newsletter:

The Water Cycle

Starting pointAs this cycle does not have a clearstarting or finishing point, we willchose that part of the cycle that tiesin most appropriately with thatparticular edition of Geijkt Nieuwsand in doing so will fulfil our aim ofpresenting all relevant equipment atspecific times.

Every stageIn its comprehensive product rangeEijkelkamp carries measuring andsampling equipment that is suitablefor measurements and sampling

throughout every stage of the watercycle. In this edition we will featurethe part shown below that relates tomeasuring soil moisture.

Soil moistureThe moisture content in the soil isone of the determining factors foroptimal plant growth and cropproduction. Moisture content in soilalso plays an important role inenvironmental research intoacidification and pollution.Eijkelkamp Agrisearch Equipment hasthe following equipment available:

• Soil moisture measuring system using gypsum blocks

• Watermark soil moisture measuring system

• Tensiometer (set)• Standard tensiometers• Jet-fill tensiometers• Quick draw tensiometers• Electronic tensiometers (Tensiors)• Thetaprobe• Profile probe• WET-sensor• Aquaflex• e+ SOIL MCT sensor• Trime FM-2 and FM-3• Trase / Mini Trase• Rhizons

A new item in Geijkt Nieuws is the ‘water cycle’. Every three months a new part of the water cycle will behighlighted and any equipment associated with it that is available from Eijkelkamp Agrisearch Equipmentwill also be featured.

11

5

PhD-projectTo end the controversy, theDepartment of Geo-EnvironmentalSciences of the Vrije UniversiteitAmsterdam initiated a PhD-projecttitled: “Hydrology andbiogeochemistry of Heath Forests ofcontrasting stature in CentralKalimantan, Indonesia” with financialsupport from the NetherlandsFoundation for the Advancement ofTropical Research (WOTRO grantno.W76-217) in October 2001. To test the drought stress hypothesisvarious types of TDR equipment andrecording tensiometers wereinstalled. This along withgroundwater tubes in four plotshaving different types of forest alongthe gradient: Lowland Forest on Clay,Tall Heath Forest, Medium HeathForest and Short Heath Forest (all onsand) in the Barito Ulu area in theheart of Borneo.

TDR equipmentThe TDR equipment consists of theTRIME EZ, the TRIME FM tube probeand TDR 3-wire probes, with the lasttwo being read using a TRIME FM3device. Whereas the TRIME FM tube probegives us daily readings at depthintervals of 5 cm, the TRIME EZprobes provide us with a continuousseries of 30-minute soil moisturecontent readings at single depths.The latter gives information on howfast the soil is replenished after a

shower or how fast it dries out (on ahalf-hourly basis, although one-minute measurements are possiblewith this instrument). Finally, the TDR3-wire probe supplies information onthe spatial variability of topsoilmoisture in the various plots.

TensiorNext to a considerable number ofmanually read tensiometers toaccount for spatial variability in soilwater tension, TENSIOR recordingtensiometers have been installed innests of 3 tensiometers per plot,installed at different depths. Soilmoisture tensions are recorded every15 minutes and stored on a custom-made datalogger system on whichgroundwater levels are stored aswell. Each tensiometer nest issupplemented with a TDR accesstube for daily soil moisture contentreadings with a TRIME FM tubeprobe at 5-cm intervals. Theadvantage of having both soil watertension and moisture contentmeasured at the same depth is thatone obtains field pF-curves fornatural wetting and drying cycles ofthe soil which hopefully leads tomore realistic modelling of the soilwater dynamics in the respectiveforests.

AnswerTogether with the continuousrecording of climatic variables abovethe forest canopy, and of tree

sapflow rates using DynagageSapflow gauges, we hope that thesesoil water measurements can beused in a soil-vegetation-atmosphere-transfer scheme. This toanswer the question whether andhow often the various types of HeathForests are subject to water stress.The nutrient deficiency and soiltoxicity hypotheses are beingaddressed through separateexperiments. For more informationon the project please do not hesitateto contact the field researcher and /or the project supervisor:

Field researcher:Ronald Vernimmen MSc (phone: +31 20 444 7334, e-mail:ronald.vernimmen@geo.falw.vu.nl).

Project supervisor:Dr Sampurno Bruijnzeel (phone: +31 20 444 7294, e-mail:sampurno.bruijnzeel@geo.falw.vu.nl)

There is a long standing debate in tropical ecology as to what are thecauses of the distinctive features of so-called Heath Forest. HeathForests are a distinctive type of Lowland Evergreen Tropical RainForest found exclusively on extremely acid white sand soils. Theseintriguing forests have much smaller trees and above-ground biomassthan ‘ordinary’ Rain Forest on clay soils, while in addition HF leavesare small and leathery. All this gives the impression that HeathForests may be subject to regular drought stress, despite theabundant equatorial rainfall. Other theories advanced to explain thepeculiar features of Heath Forests include nutrient deficiencies andtoxic conditions in the soil.

The ‘Heath Forestenigma’

creates an electrical field around themeasuring probes. Depending on thecomposition of the soil the pulse isreflected with greater or lesserspeed. Examples are: Trase, MiniTraseand Trime (FM2 and FM3).

b) FDR: Frequency DomainReflectometers (Capacitancesensors) The sensors consist of 2 electrodes(probes or metal rings). Theseelectrodes generate a high electricalfield. The soil between the twoelectrodes draws energy from this.This causes the fase of the electricalfield to change. The greater thewater content of the soil, the moreenergy is drawn off. Changes infrequency mean changes in theelectronic characteristics of the soil

which is being measured. In thesame way as with TDR, thoseelectronic characteristics also dependon the volumetric percentage ofwater in the soil. Examples are:

Aquaflex, Thetaprobe, Profileprobe,WET sensor and the e+ SOIL MCTsensor.

Measuring systems for soil watersuction tensionWater in the soil is attracted, as onemight say, by the soil particles towhich it adheres. When the soil iswet it means that many of the smallas well as the large pores in the soilare full of water, meaning that thewater is able to flow fairly easily.When the soil dries, the water firstdisappears from the large pores andthen from the small ones in which itis retained with more force – and it isthis force that is also called suctiontension or power. Suction tension isan important unit used in theagrarian as well as the green sectors.

Examples of measuring systems thatmeasure suction tension are: theTensiometer / set, standardtensiometers, Jet-Fill tensiometers,Quick draw tensiometers, Electronic

Measuring systems that show soilmoisture content as a volumetricpercentageThe soil is made up of three differentelements: soil particles, water and air.The measuring instruments from thisgroup take measurements in aparticular soil volume and determinewhat percentage of that volumeconsists of water. The volumetricpercentage of water can beconverted with the use of a pF curveinto soil water suction tension. Thewater volumetric percentage is avalue that is of particular importancefor hydrological and agro-scientificresearch.

a) TDR: Time DomainReflectometersThe measuring principle involves the

use of metal measuring probes thatact as transmitters of a TDR signal. Ahigh frequency pulse is sent alongmeasuring probes and a cable that iscalibrated to an exact length and this

6GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com

The soil moisture sensor range An important part of the Eijkelkamp product range is made up of different soil moisture sensors. Inaddition to the e-SENSE with its unique e+ sensors, a system developed entirely by Eijkelkamp itself,Eijkelkamp can also offer a number of alternatives. The measuring systems are divided into 2 groupsbecause soil moisture can be expressed in 2 important units: in volumetric percentage (water content inthe soil expressed in % terms) and in soil suction tension (the energy required to extract available waterfrom the soil). A description follows below of the types of measuring systems Eijkelkamp can offer:

7

PRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWS

PRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWSPRODUCT NEWS

e+ SOIL MCT sensorEijkelkamp Agrisearch Equipment hasdeveloped a new Soil Moisture,Conductivity and Temperature sensor inits e+ sensor product range. Measureddata are stored internally and can betransferred to the user via the e-SENSEtelemetry system or directly to ahandheld readout or PC.

Measuring principlesPermittitivity and conductivity are electricalproperties of materials. The permittivity is a

measure for to what extend the material canbe polarized. Because water is a bipolarmolecule it has a high permittivity value,while dry solid materials and air have a lowpermittivity value. Therefore, the permittivityvalue of wet materials is dominated by itswater content. The measuring principle ofthe sensor is based on the Frequency DomainMethod (FD), described by van Balendonckand Hillhorst (IMAG), at a excitationfrequency of 30 MHz, from which the systemderives:• Permittivity• Conductivity• Temperature

11tensiometer and the Mini Tensior.

a) TensiometerA tensiometer is a transparent plastictube which has a porous ceramic cupfitted at the lower end. This tube isfilled with demineralised or boiledwater. Next it is placed in the soilwith a special auger or drill. As soonas the soil dies out, a small amountof water is drawn off through theceramic cup and the tube. Thissuction tension or power can be readwith the use of a manometer that isattached to the top of the plastictube.

b) Gypsum blocks / WatermarksGypsum blocks and Watermarksemploy the simple principle ofelectronic resistance. Two electrodesare used to measure the resistance inthe gypsum blocks. When the soilcontaining the gypsum blockbecomes wet, the pores in thegypsum fill up with water causingpart of the gypsum to be dissolved.The water then conducts theelectricity independently from the

salt content in the water. The wetterthe block becomes (and thereforealso the soil) the lower the electricalresistance in the block. When the soilaround the block dries out the wateris drawn from the block. The waterdisappears from the large pores firstand then from the smaller ones. Theelectric current between the 2electrodes now needs to travel alonger distance through smallerpores, causing the resistance to beincreased. This resistance can beconverted into suction tension. TheWatermark works on the sameprinciple as the gypsum blocks. Inthe case of the Watermark thegypsum block covered by granulatefilling and cased in a synthetic coverwith perforations which extends itslife. In addition it is also moreaccurate because a temperaturecorrection can also be performed.Both measuring systems (Gypsumblocks as well as the Watermarks)come with a handheld meter.

8

C O L O F O N© 2003 - Geijkt Nieuws is published byEijkelkamp Agrisearch Equipment.Nijverheidsstraat 30, 6987 EM GiesbeekT +31 313 88 02 00F +31 313 63 21 67E eijkelkamp@eijkelkamp.com

Editorial address:Eijkelkamp Agrisearch Equipment.PO box 4, 6987 ZG Giesbeek,the Netherlands

Editors:Laura van der Lecq

Printing: Drukkerij Hooiberg, Epe

News

GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com

Software

The universal software programLogger Data Manager (LDM) hasbeen developed to increase the easeof use of the Diver. LDM enables youto program and read out themeasurements from dataloggers, andto view the measurements. Theprogram creates a database,therefore it is no longer necessary tostore each set of measurements readout from the dataloggers in separatefiles. When you read out themeasurements from a datalogger,the data is automatically storedunder a unique combination oflocation code, logger serial number,date and time. This precludes theaccidental overwriting of oldmeasurements with new measure-ments. Logger Data Manager offersmore opportunities to save thedefault settings.

Programming LDM can be installedon a desktop orportable PC and worksunder Windows 95,2000 and Windows NT(4.0). The standardread-out unit isattached to the PC.The read-out unitprovides the linkbetween the Diver and LDM. UsingLDM makes programming the Divereasy. Once programmed, the Divercan be deployed in the field.

Reading out The internal memory can be read outas soon as required. This involvesattaching the Diver to a (portable) PC

by means of the read-out unit. Thedata, the groundwater levels and thetimes at which they were recorded, isdownloaded directly into thecomputer. The data can be displayedin either graphical or chart form. It isalso possible to convert the dataformat directly so it can be processedin a spreadsheet program.

Dataprocessing The Logger Data Manager softwareis equipped with a barometriccompensation wizard speciallydeveloped for the Diver. This toolmakes it possible to correctgroundwatermeasure-ments stepby step tocompensatefor changesin the

atmospheric pressure during themeasurements period. It also makesit possible to relate the measure-ments to a specific reference point,such as the top level of the borehole.

Logger Data Manager11

Wasser Berlin, Germany7 to 11 April

Demo day Germany10 April

Demo day University Ghent,Belgium19 and 20 April

Demo Sonic Belgium15 to 16 April

Meteo Hydex Geneva,Switzerland6 to 8 May

Consoil Ghent, Belgium12 to16 May

Distributor seminar Giesbeek,Holland20 to 23 May

Water ManagementExhibition Kielce, Poland16 to 17 June

The management of groundwater resources is of vital importanceworldwide for nature, agriculture and for the supply of drinkingwater. The need to measure and record groundwater levels isbecoming increasingly apparent to all parties involved. The Divergroundwater dataloggers are at the cutting edge in the market forthis application. Eijkelkamp has been selling Diver® by Van EssenInstruments for over five years worldwide.

C a l e n d e r