Lincoln University, Irrigation New Zealand, Ballance Agri-Nutrients, Fertigation Systems and Molloy Agriculture with extra money from the Sustainable Farming Fund are working with Pamu to see if fertigation improves yield and nitrogen efficiency and whether it has lower environmental losses than solid nitrogen.
Researchers Tommy Ley of Lincoln University and Steven Breneger of Irrigation NZ are running the trial.
Breneger says Pamu approached him two years ago after hearing he’d been interested in fertigation most of his career in his native Australia and in NZ.
“The rest of the world do it and we don’t so I’ve been pushing the barrow for about nine years here,” he says.
Fertigation is used in horticulture here but till now hasn’t really been picked up by pastoral farmers.
“Pamu had been doing some thinking about how it can reduce nitrogen loss with a more aggressive reduction than five or 10%. So it was really about tailoring a system to its wants and needs.
“I did three concept designs from what they told me, based on capital cost, farm management and risk and they picked the one that met the majority of their needs.”
A 30,000-litre tank was installed on the farm and the liquid fertiliser was spread using pivot irrigators. A smaller 4200-litre tank on a trailer was rotated around the farm and connected to the bases of the pivots.
“Fertigation allows for small amounts of fertiliser to be applied at a time, allowing more uptake of nutrients by crops,” he says.
“Pamu put on about 1.3kg N/ha a week so it’s all tailored to once-a-week application.”
The trial started in November 2018 and the results at the end of the first year were encouraging. Now, at the end of the second year, a clearer picture of what seasonal nitrogen efficiency could look like is emerging.
“I went back to Pamu and asked what they were experiencing. They said ‘these are our numbers. We applied less nitrogen, we’ve grown pretty much the same grass and our milk production, given the seasons we had, was about on par with the five-year average’.”
Other benefits included increase timeliness of applications and the reduction of contractor traffic on the farm.
One year’s result wasn’t enough to prove the concept though.
“We can’t go out and say 42% is achievable because we don’t know if the grass just mined excess available nitrogen that was already in the soil. What we need is year-on-year results on multiple farms to help build the understanding of the potential benefits of fertigation.”
But part way through the second year of the trial fertigation was still holding its own compared with solid nitrogen application even though grass growth on Pamu’s farm lagged behind that being achieved by a neighbour.
“They said to me in January this is our neighbour’s pasture growth and this is ours, what do you want to do? I asked what their milk vat was saying and they said they were up on budget already.
“I asked why we were doing anything. It was a lightbulb moment and they realised nothing needed to be done.
“We’re looking at the feed value versus the feed yield so the assumption is that cows are actually utilising more of the feed more efficiently and instead of growing great tonnages of green grass we’re growing less.”
The trial is still running and final results won’t be presented till it’s completed but early indications have impressed Pamu, which has indicated it intends to expand the use of fertigation to more of its farms.
