Irrigation

The two main reasons to irrigate are:

Increased production.

Increased surety of production.

As capital investment increases then the financial risks of failure increase.

There has been a huge increase in the demand for irrigation in New Zealand.

90% of irrigation was in the South Island. With dairy intensification that figure may have increased, although there has been an increase in the use of irrigation in the lower part of the North Island for both cropping and dairying.

As well as farming activities the expansion of viticulture has added to the demand for water.

Irrigation is a world issue

• New Zealand is relatively fortunate in it’s supply of water, however this is now coming under increasing pressure.

• It is now more difficult to get a resource consent to extract water as many aquifers are fully allocated.

• In Australia for example, even having an allocation is no guarantee of getting water.

• In New Zealand a lot of water is extracted through bores on individual farms, larger schemes have water flowing in open channel or canals. This makes our water relatively cheap.

• FAO Food and Agriculture Organisation recognise water as being one of the most important issues for the next few decades.

How much have we advanced over the last few 1000 years?

THE NILOMETERA CORKSCREW STAIRCASE, CONNECTED TO THE NILE THROUGH AN

UNDERGROUND TUNNEL, MEASURING TIME AND SIZE OF FLOOD

716 AD The Nile River River Height Monitoring

THE PHILIPPINE RICE TERRACES – AN IRRIGATION SYSTEM

WHICH HAS SUPPORTED A COMMUNITY FOR 2000 YEARS

The Philippines

A 2000 year old irrigation scheme

256BC – DUJIANGYAN IRRIGATION SYSTEM

OLDEST IRRIGATION SYSTEM IN THE WORLD, STILL IN USE.

INSTEAD OF USING DAMS IT CHANNELS AND DIVIDES RIVERS.

SUPPLIES WATER TO 720,000 HA FARMLAND.

256BC China

Today centre pivots deliver water with millimetre accuracy.

1947:

Centre pivots invented, Nebraska

Quarter million world-wide

supply water to 14 million

hectares land

But how much water to apply ?

How much water do we actually

use?• In cropping we may use anything from 150mm to

350mm depending on the crop and weather conditions.

• Take for example an 800ha cropping farm, which will irrigate to an average depth of 200mm.– Imagine a rugby pitch which is 100m by 70m, the

volume of water used is equivalent to covering that pitch to a depth of 229m.

– Or, imagine the site in front of the Rugby Institute is 250m by 150m, that site would be covered to a depth of 43m.

Water use in dairying

• In dairying figures have been published suggesting we use a 1000 its of water to produce a single litre of milk.

• Take a 300 cow herd on 80 ha of irrigated pasture. The water use in the dairy shed is:

300 days * 300 cows * 70 lts per day = 6300m3

• Drinking water, provide an average over the year of 40 litres per cow per day is:

= 365 *300*40 =4380m3

• Irrigation over farm to a depth of 300 mm. 240,000m3

• Back to our rugby pitch, use in the shed, covers it to a depth of 0.9m, drinking water requires a further 0.6m and irrigation requires a volume of water equivalent to a depth of 34m over the rugby pitch.

Economic Benefits

• The economic benefits of irrigation for New Zealand are

estimated to be over a $1 billion per annum.

• Irrigated farms are 4 to 10 times more productive than

their dry land counterparts. Clearly this depends on

climate and soil type. (Soil moisture holding capacity)

• Benefits on an individual farm depend on:

– Crop/production system type.

– Risk of dry conditions.

– Farm layout and topography.

– Water resources.

Irrigation Requirements

Before deciding on investing in an irrigator a risk assessment should be

conducted to establish the financial case.

Crop Response to Irrigation

Crop Average Yield Response

Tonnes per mm of irrigation

Cereals 0.018

Grassland 0.025

Peas 0.04

Potatoes (main crop) 0.08

Vegetables

Beans Broad Processing 0.04

Cabbage early summer 0.14

Carrots 0.03

Onion 0.08

Fruit

Apples 0.015

Raspberries 0.025

Strawberries 0.025

Centre Pivot, how it operates

A central pivot around which

the irrigator rotates.

Made up of sections which are

powered by electric motors,

the outside section moves first,

then the next, they only move

a controlled distance. There

are sensors that detect how far

the outside section has moved

by measuring the angle

between the sections. The

sensor is used to stop the

section going too far. Once the

section has moved it’s preset

distance the one nearer the

centre will move.

Centre Pivot Control

The speed of the irrigator is controlled by an electronic control system, which

allows the operator to set the application rate required and hence the travel

speed as output in terms of water flow is usually fixed.

Most units will move a set distance each time, but the time between moves is

simply shortened to speed up the irrigator and reduce application rate.

Some have the ability to automatically irrigate different areas (crop blocks) at

different rates, once the information has been entered into the controller.

Controlling factors

• The three criteria used to control the irrigator are:– Infiltration Rate

– Soil Water Holding Capacity or more correctly the soil moisture deficit at the time of irrigation.

– Crop requirements

• Infiltration rate is important as we do not want to exceed this as this will allow surface run-off to occur.

• Soil Water Holding Capacity, it is pointless to exceed the water holding capacity as water will simply drain from the profile. This is expensive, inefficient and possibly adds to nutrient leaching. We need to consider the “readily available water” as water uptake will be restricted before water is completely used up in the profile.

• Crop requirement, clearly these are dependant on the two above, but crop requirement will determine return period for the irrigator. This needs to be scheduled.

Suggested Application Rates

Soil Texture Infiltration

Rate

Application

rate mm per h

Course sands, fine sands, loamy sands. Very High 12 – 20

Course sandy loams and fine sandy loams High 7 - 15

Very fine sandy loams, sandy clay loams

and silty loams.

Moderate 5 - 9

Clay loams and silt clay loams Low 4 – 6

Sandy clays, silty clays and clay Low 4 or less

Application Rates

• Must ensure surface run – off does not occur. These rates are suggested maximum application rates.

• They apply to bare soil. With full crop cover you can add 20%.

• These rates are for level ground. For slopes of 5 – 10 per cent the application should be halved.

• Water infiltration rates are generally higher to begin with but drop to these levels rapidly.

• Remember these are average application rates.

Water Availability

Textural Class Water Holding Capacity (mm.m-1)

To 0.3m depth Below 0.3m

Sand 150 50

Loamy Sand 180 110

Sandy Loam 230 150

Fine Sandy Loam 220 150

Silt Loam 220 150

Clay Loam 180 110

Clay 175 110

Peat 200 – 250 At least 200 - 250

Irrigation Trigger Point

SATURATED WILTING POINTIRRIGATION

TRIGGER POINTFIELD CAPACITY

SHOULD WE ADD UNIFORM DEPTH OF IRRIGATION TO VARIABLE SOILS?

IRRIGATION

TRIGGER POINT

Soil moisture monitoring

Soil FC AWC RAWC Trigger

Point

Ohakea silt loam 0.39 0.17 0.09 0.30

Ohakea loamy sand 0.35 0.16 0.08 0.27

A

B

C

A

B

C

PONDED

AREA

Site without irrigation

Site 3 No Irrigation, Yield 6 T/ha

Plant Available

Water 72 mm

Soil moisture Measurement

a, b, c, d Rainfall events

1st Nov 1st Dec 1st Jan 1st Feb

Rainfall utilised 75mm, soil moisture 72mm to 50% AWC.

Actual water used 182mm, but growth restricted

Moisture content at field capacity

Moisture content at 50% AWC

a

b

c d

Irrigation Schedule: Site 1 High yielding 11 t/ha

Rainfall 165mm, effective rainfall 146mm, soil moisture 79mm to 50% AWC.

Effective irrigation used 240mm. Delivered irrigation 255mm, total water use 440, effective water use386mm

Plant Available

Water 79 mm

Soil moisture Measurement

1 to 4 irrigation events

a – m Rainfall events

1st Nov 1st Dec 1st Jan 1st Feb

Moisture content at field capacity

Moisture content at 50% AWC

1 2 3 4ab

m

Irrigation Schedule: Site 2 Irrigation with moderate yield 8

T/ha

Plant Available

Water 57 mm

Soil moisture Measurement

1 to 6 irrigation events

a – p Rainfall events

1st Nov 1st Dec 1st Jan 1st Feb

Moisture content at field capacity

Moisture content at 50% AWC

1

23

4

a b5

p

6

Delivered irrigation 255mm, Effective 225,

Actual rainfall 163mm, Effective 130mm

Total water used 418 mm, Effective 335 mm

Differences to consider

• Unirrigated site the readily available water was 72mm, – site 1; 79mm

– site2; 57mm.

• Clearly the management at site 2 allowed the soil to become sufficiently dry to stress the plant. Soil would make that more likely to happen but management should be alert to that. It happened right from the start and they repeated the mistake on other occasions.

• Water use is practically identical, yet yield is 3 t.ha-1

more on site 1. Was irrigation economical on Site 2? This land would not be capable of growing cereal if irrigation was not employed.

• Consider these three cases for a risk assessment. Site 2 and the non-irrigated site are 8 km apart.

Centre Pivot Length (m) Area under irrigation (ha)

600 113

800 201

1000 314

1500 707

2000 1257

Using water guns on irrigators

Guns are often attached to the ends of the centre pivot in order to get better reach,

some have arrangements that mean they can adopt a more elliptical footprint, this

added to the gun means that square block can almost be accommodated.

The evenness of distribution under these guns is generally inferior to the actual

sectors of the pivot.

Coping with slope and

infrastructure

Centre pivots can have some flexibility, remember application rates on sloping

land.

Gateways and fencing can be designed that allow the irrigator to travel without the

need use labour to open gates or move fence lines.

Accidents do happen

Lateral

Individual sections very similar to centre pivot, biggest difference is in the way that

a farm is organised. Best suited to a large rectangular blocks with a water supply

through the middle of the block.

Takes time to turn around.

Wheels in motion in parallel, again sensors used to keep individual wheel sets in

line.

Irrigator layout on farm

Direction of travel

Water

Sourc

e

Direction of travel

Irrigator

rotates

around

Takes time to move the irrigator, higher labour requirement as a result.

Plus some additional wheeling damage done to crop. Water supply piped or canal.

Sprinkler Irrigation

Can be setup for different and small areas, time consuming but flexible.

Lower capital cost but higher labour input.

Not a lot of computer aided control accept timers perhaps.

Moveable rotary systems

Rotary irrigator with 150m span, as irrigation starts the unit is pulled up on an

anchored cable. Cable winch is on the irrigator.

The water supply pipe is also dragged through the crop. Care must be taken to

reduce crop losses. In one study we measured 11% of crop affected by wheeling

etc.

Less infrastructure than centre pivot or lateral but more labour intensive. Speed of

application is also reduced as only a small area is being covered at any one time.

Farmers are more likely to use too high an application rate with this equipment.

Moveable boom system

Similar to moveable rotary but irrigation unit much lighter, hose is wound in to

move the unit up the field.

Smaller than rotary systems but suitable for vegetable crops etc

Lower throughput in terms of ha/hr but a relatively simple system and water should

be applied more accurately than an irrigation gun for example.

Higher labour requirement.

An option for contract growers.

Drip tape irrigation

http://www.cdpr.ca.gov/docs/whs/pdf/hs1861.pdf

www.netafim.co.nz

Use of high accuracy steering systems has increased the interest in using drip

tape, water use is more efficient because of reduced evaporation compared to

spray systems. Relatively cheap infrastructure, low pumping rates, etc.

High accuracy steering may mean that they can be used in the same position for a

number of years and cultivated around, chances of doing that with manual driving

not good.

Gun Irrigation

Large unit used to apply water in a swath,

problems can occur because of the water

droplet size and energy, causing erosion.

Greening in potatoes for example where soil is

eroded from the drill or bed side.

Similar in setup to moveable boom unit.

www.oznet.ksu.edu/library/agec2/mf836.pdf Comparison of costs

www.similima.com/ppt/spm12.ppt Irrigation costs in developing countries,

powerpoint presentation

Some useful sites

http://www.maf.govt.nz/sff/about-projects/search/03-098/feasibility.htm

Manuherikia Valley Feasibility Report

http://www.dpi.nsw.gov.au/agriculture/resources/water/irrigation/costs/cost-

calculator

Some items may not fir for NZ conditions but demonstrates procedures used in cost

calculation.

http://agalternatives.aers.psu.edu/Publications/irrigation_fruit_veg.pdf –

Penn State Extension document on irrigation of fruit and vegetables.

http://www.irrigationnz.co.nz/ Irrigation New Zealand