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Pasture irrigation on dairy farms
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Recently there has been increased interest in using water for pasture irrigation on diary farms in Taranaki. Water from rivers and streams is generally the easiest and cheapest option, where it is available. However, the amount of available water is limited due to the relatively small catchments in the region.
The Council commissioned a report to assist with planning for and managing water resources in the region. The report provides information on how to manage the allocation of water for pasture irrigation, taking account of appropriate application rates for Taranaki's climate and soils, appropriate irrigation systems and their use and efficiencies, and areas that might be suited to irrigation.
The report Optimisation of Farm Irrigation is summarised below. The guidelines will assist irrigators and the Council to assess and better manage pasture irrigation and to promote sustainable management of our valuable water resource.
A resource consent is required from the Taranaki Regional Council to take and use water for pasture irrigation.
For information on applying for a resource consent contact the Council's Consent Staff.
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Irrigation Demand & Management in Taranaki
Irrigation Zones
For the purposes of determining irrigation demand and management the Taranaki region can be subdivided into eight zones as shown below. The zones encompass the area of irrigable lands, and are classified into three levels of potential; low, medium and high based on financial benefit over the long-term.
Water Demand
Irrigation water demand is related to climate, crop type and soil waterholding capacity. The table below lists the take rate, daily and maximum annual demands for the zones. These rates and volumes are based on gross water demand, and assume typical efficiency levels for sprinkler irrigation.
|
Zone |
Take Rate (l/s/ha) |
Daily (m3/d/ha) |
Annual
(m3/ha/yr) |
|
1 |
0.40 |
31 |
2,200 |
|
2 |
0.51 |
40 |
4,840 |
|
3 |
0.63 |
50 |
6,400 |
|
4 |
0.63 |
50 |
5,120 |
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5 |
0.63 |
50 |
4,200 |
|
6 |
0.63 |
50 |
3,600 |
|
7 |
0.53 |
42 |
4,000 |
|
8 |
0.46 |
37 |
3,960 |
The above table is a useful guideline to irrigators and resource manager, of 'reasonable' rates and allocations to meet daily and peak crop water requirements.
Irrigation Methods
A variety of irrigation methods are suited to irrigation of pasture, as listed below. No one method is suited to all situations, with selection dependent on cost, labour requirements, farm-layout and irrigation requirements.
|
System |
Cost |
Labour |
CU* |
|
K-line |
Low |
High |
60-70% |
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Long-lateral |
Low |
High |
60-70% |
|
Centre pivot |
High |
Low |
70-80% |
|
Boom irrigator |
Medium |
Medium |
70% |
|
Gun irrigator |
Medium |
Medium |
60-70% |
* CU coefficient of uniformity is indicative of application efficiency.
In Taranaki wind is a key factor affecting application uniformity. High winds distort wetted patterns and can lead to high losses. In areas of high winds during the irrigation season, system design needs to take into consideration wind frequency and direction, with sprinkler spacing reduced to maintain uniformity and efficiency.
Application rates vary between irrigation methods from less than 5 mm/hr for K-line and Long-laterals to more than 15 mm/hr for gun irrigators. The rate should be less than the soil infiltration capacity to minimise surface run-off losses, particularly on undulating sites. However, Taranaki soils are generally free-draining with high infiltration capacities.
Irrigation Management
The key elements of irrigation management are application depth (mm) and return interval (days). The return interval is dependent on crop water demand and soil water content. The table below lists application depth and return interval for the eight irrigation zones.
|
Zone |
Application Depth* (mm) |
Return Interval (d) |
|
1 |
44 |
14 |
|
2 |
44 |
11 |
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3 |
30 |
6 |
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4 |
30 |
6 |
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5 |
30 |
6 |
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6 |
30 |
6 |
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7 |
50 |
12 |
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8 |
44 |
12 |
Note: for local areas of low waterholding sands application depth and return intervals should be reduced to minimise drainage losses
Typically the irrigation cycle is started when half the soil water has been depleted. This can be determined by directly monitoring of soil moisture levels (such as by neutron probe, tensiometer or TDR) and/or calculation of soil water balance based on rainfall and evaporation (with an evaporation pan).
Contact the Land Management Section for information or advice about sustainable land management or how to obtain a farm plan.
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