For the last six months his Canterbury cropping farm hasn’t leached any water, but the data was not reflected by Overseer as it could not handle spatial accuracy, he said.
“Our cropping farm, on average, should have leached 20kg N/ha by the model. But if I haven’t had any leaching for six months, how have I leached any nitrogen because I’ve had no water go anywhere?”
The nitrates and other nutrients had stayed in the root zone exactly where they were needed, he said.
The farm had 35 different soil moisture probe sites and through the season there was only one site that ever hit the full point.
“We are saving, on average, 32% of our water. We have captured every rainfall event along with irrigation and still stayed within the optimal soil moisture parameters. So if we’ve never hit the full point, we’ve also never leached anything out of the profile.”
Even with actively managed irrigation on Overseer, the model struggled to reflect this data, he said.
Agri Optics Electro Magnetic soil mapping technology reads the soil’s water holding capacity and could be used by farmers to maximise efficiency by irrigating on certain soils at the right time, he said. Farmers could further reduce nutrient leaching with the company’s Smart-N technology, which involves targeted fertiliser applications to the point of avoiding urine patches in the paddock while applying nitrogen.
Trials in Australia had consistently shown 30-40% saving in nitrogen fertiliser without any reduction in pasture growth, he said.
“To be honest, this doesn’t fit within Overseer. Overseer might only give you about a 5% or 10% benefit at most. That’s not to say the model is faulty. We have to work towards helping to validate it to be more accurate model.”
He was keen to work with the developers of Overseer on the absolute numbers from his farm to show what the real benefits were. Councils using Overseer to benchmark farmers had to be aware the model would continue to be upgraded.
“If councils want all the data and to be really accurate, then the onus is on them to have a really accurate model,” he said.
Overseer, while not delivering as well as it could, was a starting point for farmers to benchmark themselves. But farmers using precision technology were ahead of councils at present, meaning these bodies would be hard pressed to legislate against these landowners.
