Dry matter doubled after changing irrigation schedule

By Rick Bayne

FARMERS COULD double their pasture production by getting their irrigation timing right and avoiding a “green drought”, a dairy research symposium has been told.

Speaking at the Dairy Research Foundation’s 2018 Symposium at the University of Sydney, senior research fellow Dr James Hills from the Tasmanian Institute of Agriculture said the Smarter Irrigation for Profit project showed farmers were experiencing significant losses through inefficient use of irrigation.

The project monitored five dairy farms over three years and in one case a Cressy farmer was able to boost his average pasture growth rate over the irrigation season from 34 kg DM per hectare per day to 69 kg DM primarily as a result of modifying his irrigation scheduling practice.

“We found their production was typically half of what they could potentially be producing,” Dr Hills said. “There were significant issues with their irrigation practices and a massive opportunity for improvement.”

The Cressy farm had a 117-hectare pivot. In the 2015–16 irrigation season they used 6.2 megalitres of irrigation per hectare but because their irrigation scheduling wasn’t right and they weren’t producing optimal pastures, they had to buy in grain, which the farmer calculated as more than $70 000 in unnecessary feed cost.

Dr Hills said the farmers in the study were allowing soil moisture to dry to below the refill point.

“They need to make sure there is enough moisture in the soil so the pasture can easily use it; between the refill point and the field capacity,” he said. “If you starting dropping below that zone you’re going to stress the plants and you’re not going to get good growth.”

Dr Hills said farmers were typically delaying irrigation start-up too long after a major rain event, leading to soil moisture dropping below the refill point; then their irrigation system wasn’t putting enough in to lift soil moisture back into the readily available water zone.

“They need to start their irrigator a lot earlier after rain and keep it going. If they allow the soil to dry too much and then put the irrigator on, in the middle of summer they’re often only replacing what they’re losing in evapotranspiration and never catching up.

“Irrigating when in deficit below the refill point will keep the pasture green but won’t allow it to grow to its maximum potential. We call it the green drought and we’ve noticed it again and again.”

Dr Hills said the project had shown farmers that poor watering can be costly because they’re not allowing pasture to grow to potential.

“Typically, you can grow 80 kg DM per hectare per day but if you get into the green drought scenario you tend to halve that production.

“We were able to show that if you keep water in your readily available water zone you can significantly increase pasture production, simply by improving scheduling.”

Dr Hills said farmers don’t need to use more irrigation; they just have to get the timing right. “Keeping the bucket topped up is key.”