Sarah Clack
Dairy Extension Officer
Together with water allocations not reaching 100 per cent and the resulting high temporary water costs, there is a greater necessity to use water effectively and efficiently this autumn.
Each farm business will have differing water resources. With this, decisions will be made on how best to use this valuable resource based on an individual’s situation, skills and requirements.
The amount of irrigation water available will impact on the timing of sowing, the area sown at a given time and also what is sown.
There will be a number of questions you may be asking:
- How much water do I have?
- How much water do I use in a normal season?
- Is purchasing water an option? If yes, how much is available?
- How much feed do I require and when?
- What are the alternative feeds available, either on-hand or available for purchase?
The time of first irrigation or irrigation start-up will impact the number of irrigations required for the pasture or crop and therefore how much water will be needed. The earlier in the autumn the irrigation start up the more irrigations will be required.
The first irrigation typically uses 1.5 ML/ha with subsequent irrigations requiring 0.5 ML/ha, depending on soil type and irrigation layout.
The table illustrates the typical number of irrigations required for autumn sown pastures at different start up times, the anticipated yield under dry, average or wet conditions, and the additional t DM grown for each ML of water applied.
The pasture growth figures are for a well-managed ryegrass pasture.
Depending on the season, the number of irrigations could vary by one or two more if dry or less if wet.
It is a balance between water available and feed demands with later start up dates increasing the time until the first grazing due to cooler temperatures and reduced daylight hours.
If sowing in mid-March, it may be reasonable to expect first grazing to occur six to eight weeks post sowing while for a pasture sown in early June first grazing may not occur until 8-12 weeks post sowing.
Staggering irrigation start-up helps to develop a feed wedge by having the growth stage staggered and helps to reduce the impact of weather conditions for example a heat event or water logging from a rainfall directly after irrigation.
| Start-up time | Number of Irrigations | Yield (t DM/ha) up to mid-August | ||
|---|---|---|---|---|
| Dry winter | Average winter | Wet winter | ||
| No irrigation | 0 (0 ML/ha) | 1.0 | 2.5 | 4.0 |
| Mid-April start | 1 (1.5 ML/ha) | 2.5 | 4.0 | 4.0 |
| Extra growth (t DM/ML) | (1.0) | (1.0) | (0.0) | |
| Early April start | 2 (2.0 ML/ha) | 3.2 | 4.5 | 4.0 |
| Extra growth (t DM/ML) | (1.1) | (1.0) | (0.0) | |
| Mid-March start | 3 (2.5 ML/ha) | 4.0 | 5.0 | 4.0 |
| Extra growth (t DM/ML) | (1.2) | (1.0) | (0.0) | |
Ensure you get the basics right to get the best establishment possible. Consider sowing depth, good soil seed contact, nutrient management, pest control and grazing management. Depending on your water availability and risk you may carry over water for one to two irrigations to ensure spring growth.
For an easy to use water budgeting tool, see .
