New DairyNZ research shows dairy farmers could reduce their nitrogen leaching by as much as 50% by stacking N mitigation options all at once.
The preliminary results from the first year of a Low N Systems trial at the Lincoln University Dairy Farm showed that while there was a 7% reduction in milk solids per hectare, there was a big reduction in N leaching, with indications of a 50% reduction.
There was also a 12% reduction in greenhouse gases and the purchased N surplus was dramatically reduced by 133% because of the drop in N fertiliser
DairyNZ principal scientist Claire Phyn outlined its findings at a DairyNZ field day at Jamie and Lu Lyons’ 280 hectare farm in North Waikato.
The research at Lincoln is now into its second season and showed that applying complementary mitigations that target different parts of the N cycle can potentially be used to achieve significant N losses.
These mitigations included reducing N fertiliser applications from 190kg/ha/year to 90kg, switching from irrigated ryegrass-clover pasture to a mix of irrigated plantain, Italian ryegrass and clover, swapping kale crop and baleage for pasture, and baleage for a wintering system.
The trial plot is also using different management techniques including low N supplements, using afternoon grazing, extended rotation lengths and using bulk milk urea to indicate dietary N surpluses.
The research comes off the back of the findings from DairyNZ’s Pasture 21 and forage research projects.
It’s been 10 years since the Pastoral 21 programme ended and, looking back, Phyn said it launched a lot of the science programmes that are active today.
It focused on ways to reduce inputs such as N fertiliser and supplements and increase outputs – milk and meat – and reduce the N surplus and improve N conversion efficiency.
The four-year trial revealed a 40% reduction in N leaching, but it came at a cost of an 8% reduction in profit.
“What they were able to demonstrate is that by combining different mitigation options you can achieve significant reductions in N leaching depending on where you are,” she said.
DairyNZ followed up this research with its Forages for Reduced Nitrate leaching study, which looked at ways to reduce plant N content to help reduce urinary N excretion and concentration.
A further piece of research is also well underway: the Plantain Potency and Practice Programme, which looks at how plantain can be used as a tool for N reduction.
“Most of the evidence found to date is around the dilution effect. Plantain has a very high water content and by ingesting it, the animals has more dilute urine,” Phyn said.
It has shown it is possible to achieve a 6% reduction in N leaching per 10% plantain in the cow’s diet.
DairyNZ is also developing a bulk milk urea indicator tool that indicates when the herd is at risk of higher N losses in its urine.
The tool could be released in the next two years with prototype testing underway with farmers.
The tool will include guidelines along with a dashboard to give farmers more information on how it can be used on the farm and support decisions around improving fertiliser and feed efficiencies.
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