The trial is testing the impact of combining different ways to reduce N losses at the research farm while maintaining a profitable business.
Among the strategies being explored are lowering nitrogen fertiliser, feeding cows on diverse pastures containing plantain and Italian ryegrass and wintering them on pasture and baleage instead of winter crops.
The research — expected to help farmers cut N losses from farms and be more efficient with their nitrogen use — was opened up to farmers on a field day during the South Island Dairying Event (Side) conference.
Pre-trial modelling with Overseer and Farmax indicated the strategies could reduce N losses from the milking platform by 30% to 40% and decrease greenhouse gas emissions by 10% — at 4% less profit.
The addition of changing winter feeding from kale crops to pasture and baleage is expected to further lower this to 50% to 60% in total N losses and about 12% in total greenhouse gas emissions at a 7% profit loss.
Agricultural sciences senior lecturer Dr Racheal Bryant said N loss mitigations were being combined and animal diets monitored to see when nitrate leaching was at risk of increasing.
"In this particular project [we want] to achieve a 40% to 60% reduction in nitrate leaching with little to no impact on other greenhouse gases or profitability or animal welfare. So it is taking a holistic approach, but the primary focus is to reduce nitrate leaching to that extent both on the milking platform and on the wintering platform."
She said support and decision tools would be provided to identify when nitrogen surpluses were happening within cows by using daily indicators in milk urea.
"We are doing a lot of research to make sure we are confident in our recommendations and thresholds ... to identify when the nitrogen in the diet is either too high or too low and that can help us manage our nitrogen to stay within the farming system.
"That is really what this project is about with the emphasis on reducing our purchasing surplus to follow the significant ways we can maintain and keep that nitrogen within the system rather than having it loading up the soils and potentially at risk of leaching out or being lost as nitrous oxide."
The Low N Systems research programme led by DairyNZ also has a 1.8ha wintering area in kale versus 3ha on pasture.
DairyNZ farm systems scientist Dr Nicole Wheadon said they wanted to play out the modelling in the trial to see if the expected leaching was achieved.
Preliminary results from the collection of 672 suction cups on the milking platform indicated there was about a 30% less nitrate leachate in the stacked farmlet, which was "promising", she said.
She said this was being paired with drainage models and deep soil, pasture and animal measurements.
"So we’re just collating all the data from the first season and it’s quite a big task. We have drawn down some results and still have some questions we need to answer and think through, but in general the key points are the average pasture cover was similar for each farmlet over the season despite the lower nitrogen fertiliser.
"But the stacked farmlet in spring had a big surplus driven by the Italian ryegrass and both farmlets had a poor summer when ME [metabolisable energy of dry matter] was quite low and in autumn we had higher growth rates than expected so we didn’t end up feeding any supplement."
Milk solids per cow were higher for the stacked farmlet as it was slightly larger and the control farmlet was higher per hectare.
Both herds had reasonably low milk urea.
Dr Wheadon said there was a big saving on nitrogen fertiliser costs on the stacked farmlet and more silage was taken because of the spring surplus, but regrassing costs were higher because of extra spring plantain broadcasting.
"Overall, the preliminary results show a 6% reduction in profit on the stacked farmlet compared with the control, which is roughly in line with the pre-experimental modelling. We will update that soon with the wintering data we have coming in."
She said the loss of profitability from the combination of stacked mitigations might have to be accepted to meet environmental demands.
"If you are dropping your nitrogen leaching by up to 50% it would be amazing to find something that would not do that, but I think 6% is acceptable."
Italian ryegrass was included because of its cool-season activity and potential with deep roots to scavenge nitrogen as well as being compatible with plantain and clovers.
Maize silage feeding was considered in the modelling, but would have increased greenhouse gases. Low nitrogen supplementary feeding was also considered in autumn, but little was needed.
Normally, cows on the research farm are wintered off at Ashley Dene Research and Development Station’s stonier soils, but scientists wanted to take soil measurements on site.
Both farmlets were sown last November with the control farmlet in winter kale and the stacked farmlet in the same pasture as the milking platform’s Italian ryegrass, red and white clover and plantain.
DairyNZ research associate Holly Williamson said the aim of the winter trial was to reduce expected leaching in real life and maintain similar cow body condition and liveweights and milk production post calving in the stacked farmlet.
"There are two main mechanisms by which the stacked farmlet will reduce leaching and the first is the pasture will continue to grow and uptake N after grazing, whereas in the kale ... any urinary N will be vulnerable to leaching events.
The target feeding allocation for control cows is 8kg of dry matter of kale and 4kg of baleage a day and stacked cows is 6.5kg of pasture and 6.5kg of baleage.
The research farm was formed in 2009 when dairying was starting to emerge in the South Island.
Today it has expanded to 188 Friesian cross Jersey cows run in small herds over 11 farmlets on 66ha under pivot irrigation.
Earlier, Prof Pablo Gregorini provided an overview of the Integral Health Dairy Farm Project at the university’s Ashley Dene facility.
More than 400 farmers and other professionals attended Side, the nation’s largest dairy conference held at the university campus.
