ENVIRONMENT DAIRYNZ
Strategies to meet the nitrogen cap Words by: Virginia Serra Selwyn Hinds project leader, DairyNZ
T
he new synthetic nitrogen (N) cap of 190kg N/ha coming into effect in July 2021 means all dairy farmers need to record both the amount and where synthetic N fertiliser is applied onfarm. This means many farmers will be considering how to make changes to meet the new requirements. In Canterbury, I’ve been leading a project with farms in the Hinds and Selwyn catchments. The farmers are trialing options to reduce N loss, including examining and changing N fertiliser use. The findings show some farmers have reduced fertiliser applications with little impact on pasture growth and profit. This project has helped understand strategies for farmers to meet the new nitrogen cap requirements.
PLANNING FOR CHANGES
Before making changes it’s important to understand the current situation. Work out how much synthetic N fertiliser was applied last year and in what areas. We recommend reviewing your current N use strategy, together with a farm advisor, to see how it can be more efficient. This includes looking at whether applications were completed as planned,
Addressing any limits to clover growth will encourage free N fixation in mixed pastures.
and reviewing application rates and fertiliser types. Considering how you will manage pasture and feed is also critical. After reviewing your strategy, work on a plan to meet the new N cap and implement a system to keep track of future applications.
OPTIONS TO REDUCE NITROGEN FERTILISER
The project has shown that farmers have reduced N fertiliser application rates through a range of strategies. Not all strategies may suit your farm, so it’s best to talk through options with a trusted advisor. • Allow time to significantly reduce N fertiliser use - If you need to make a significant reduction to meet the cap, it’s best to start now and reduce fertiliser use gradually. It’s also important to allow time for clover to re-establish so that the additional fixed N is available for growth. • Reduce N application rates and avoid wastage - Limit applications to no more than 40 kg N/ha in early spring and then to 0.8 kg N/ha per day of round length. N applications are most beneficial to fill a genuine feed deficit – such as in early spring. In areas where effluent is applied, fertiliser applications can be reduced. To avoid wastage, avoid applying N fertiliser before a significant rain or drainage event. • Increase grazing round lengths - This will help ensure grazing occurs between the 2.5 to 3 leaf stage of pasture and allow more grass growth. In Canterbury this is between 22-24 days during spring and summer. Where N applications follow grazing, increasing the round length reduces the total number of grazings and N applications per year.
Dairy Exporter | www.nzfarmlife.co.nz | November 2020
Strategies to limit urea application and using a coated product will all drive down N use.
• Have a monthly N fertiliser plan and monitor it - Several farmers have been surprised at the amount of N they used over a year that was unplanned or not monitored. To keep track of this, farmers can set an N budget and plan to report N use by paddock. • Address factors that may limit pasture or clover growth - Paddock scale soil tests successfully help identify factors including soil fertility, pH, weeds, irrigation, pasture species and drainage. • Pasture walks - Regular pasture walks can help assess a genuine feed deficit. In late autumn, pasture response can be slow while N loss risk is higher due to potential rainfall, so N applications can be reduced. When pasture growth is high, you may be able to skip a few paddocks from routine N applications. • Consider coated urea - This reduces volatilisation (the conversion of N in urea to ammonia gas). Using coated urea in the right conditions can reduce N applications by up to 10% while growing the same amount of pasture. • You can read more about the nitrogen cap online at dairynz.co.nz/nitrogen-cap. 63
