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Published: 24 Jun 2019

Cow Under Pivot

Save more, grow more

Symon Jones and Lesley Irvine, TIA

Want to save money? Recent irrigation research has shown there is great potential for dairy farmers to both save money on their irrigation costs AND grow more pasture.

Green Drought

For example, one farmer participating in the Smarter Irrigation for Profit project found they were ineffectively irrigating their pasture. This was a ‘perfect’ example of a phenomenon commonly called the Green Drought. Green Drought occurs when soil moisture has depleted too far, and the amount of water being applied is too little to replenish the soil profile. There is enough water applied to maintain green pastures, but growth rates are very low.

This common phenomenon is clearly demonstrated in the Green Drought diagram. The orange line indicates the soil moisture level. To be effective with your irrigation you want this line to remain in the green zone of the graph, indicating there is enough readily available water for good plant growth. If the orange line drops below the green zone, plants become water stressed and growth rates will slow.

green drought

You can see from the Green Drought diagram that after the large rainfall event on the 13th November (tall grey bar at the left of the graph) soil moisture levels steadily decreased. There were small rainfall events on November 21, 22 and 23. Irrigation water (blue bar; 11mm) was also applied on November 23. This increased the soil moisture level (the orange line) but not by enough to get soil moisture back into the green zone. You can see the orange line rises every time there is rain or an irrigation event, but not enough water is added to the profile until the end of December, when the soil moisture level enters the safe green zone of the graph. All the time the orange line is below the green zone, the pasture is stressed and grows slowly. The difference this makes to the total amount of pasture grown is dramatic!

In the Table, the amount of pasture grown during the irrigation seasons for the three years of the project is shown. 2016/17 is the season shown in the Green Drought diagram. In 2017/18 the amount and timing of water applications was based on soil moisture probes and weather forecasts. The average growth rate achieved in the 2017/18 irrigation season was 69 kg DM/ha/day compared to 54 kg DM/ha/day in 2016/17 and 34 kg DM/ha/day in 2015/16.

Year (Oct-Mar)Average pasture growth rate (kg DM/ha/day)Pasture grown (t DM/ha)Irrigation (ML/ha)Rain (mm)GPWUI t DM/ML
2015/1634*6.26.22150.74
2016/17549.84.13191.34
2017/186912.45.12031.65

*measured from January 2016

NB: GPWUI is the Gross Production Water Use Index. This is the amount of pasture grown divided by the amount of rainfall + irrigation.

The cost of low pasture growth rates

To fill the feed gap caused by the low pasture growth rate, the farmer calculated it cost $42,000 for other supplements. This is a significant cost that could be have been saved by applying the right amount of water at the right time. There were also other savings. The Table shows a lot more pasture was grown in 2017/18 with less water applied – again because water was applied at the right time and at the correct soil moisture deficit. This practice saves a lot of water and reduces energy costs.

Energy costs

Growing more pasture for the same water applied wasn’t the only example of saving money in the project. Energy use by the irrigation pumps was measured for 5 pivot sites.

Pivot site

kWhr/ML

$/kWhr

$/ML

1

113

$0.23

$26.08

2

157

$0.23

$36.16

3

220

$0.23

$50.65

4

304

$0.23

$70.00

5

787

$0.23

$181.05

You can see from the Table Pivot site 5 had much higher costs for pumping water than for the other sites. Using this information, the farmer at site 5 replaced the pump and motor and saved $20,000 in energy costs for the season.

Uniformity tests conducted on each pivot also highlighted issues with the evenness of water applications – even on relatively new pivots. Fixing these issues made sure the right amount of water was applied and improved pasture growth rates.

The Smarter Irrigation farmers and project team were excited about the savings achieved on each of the farms involved in the project. The project also highlighted there are potentially a lot of underperforming irrigation systems in Tasmania.

How can you save money?

For the 2018/19 irrigation season, a pilot irrigation discussion group was established in Meander. The pilot involved an irrigation focus farm with soil moisture monitoring equipment and a weather station installed. The focus farm and other participating farms all weekly measured their pasture growth. The pasture growth data obtained along with soil moisture and weather data was shared with the group each week. The data was used to help make key decisions on irrigation scheduling. A monthly on-farm discussion was held, and the discussion topics were determined by the group.

There were some really interesting discussions held with each farm identifying improvements they could make to their irrigation system, including: better scheduling, installing soil moisture meters, installing boombacks to reduce wheel track damage, and conducting more physical checks.

This pilot group found great value from participating in an irrigation specific discussion group and are keen to continue. Further funding is being sought to increase the project to several more irrigation focus farms and discussion groups. If you are interested in being involved, please contact Symon Jones on 0418 876 089 or Samantha Flight on 0409 801 341. There are big savings to be made!