SYSTEMS NITROGEN FERTILISERS
Wearing the nitrogen cap Advice and top tips from farmers, farm consultants and scientists involved in the Meeting a Sustainable Future project have contributed to getting fertiliser rates down to meet new national freshwater nitrogen caps. Anne Lee reports
H
igh users of nitrogen fertiliser are being urged to start lowering nitrogen rates this season to try and reduce the potential for dramatic impacts on their farm systems when new national freshwater nitrogen cap rules come in. The 190kg N/ha/year cap on nitrogen fertiliser application for each hectare on the farm will begin in July next year under the Labour Government’s new rules. Farmers will have to report their synthetic fertiliser nitrogen use to their regional councils. Canterbury farmers are likely to be hardest hit by the new input rule which had not been signalled in last year’s proposed policy statements that drew record numbers of farmer submissions. DairyNZ Meeting a Sustainable Future project leader Virginia Serra says DairyBase 58
data shows for the 2018/19 season average nitrogen fertiliser use in Canterbury was 234kg N/ha effective. The average for the past 12 years reported for Canterbury farms in DairyBase was 226kg N/ha effective. The figures are backed up by data from farms involved Virginia Serra. in the Meeting a Sustainable Future Project where farmers are partnering with DairyNZ to work together on solutions to reduce nitrogen losses and implement practical solutions borne from research studies including the Forages for Reduce Nitrate Leaching study. Partner farmers averaged application rates of 218kg N/ha for the latest year end which was down 11% on the groups
average of 244kg N/ha over the 2009-2013 baseline period. An established consultancy firm in Canterbury reported its clients averaged 235kg N/ha for the 2019/20 season with several clients applying more than 300kg N/ha. Irrigated Canterbury farms can usually expect high response rates of 10-15kg drymatter (DM)/kg of nitrogen fertiliser making nitrogen boosted pasture a very price competitive feed which explains the higher rates, Virginia says. Despite those response rates though the relationship between nitrogen fertiliser and profit is low according to DairyBase data analysis. Much of the focus of research and farmer projects has been on the major culprit driving nitrogen loss onfarm – nitrogen deposited at high rates in the urine patches from cows. Managing irrigation to limit drainage also has a significant impact on helping keep losses down. But Overseer is responsive to reducing nitrogen fertiliser with nitrogen fertiliser correlated to nitrogen surplus and nitrogen surplus highly correlated to leaching, so lowering rates will go some way to achieving environmental goals - providing of course the nitrogen isn’t substituted with other inputs such as bought-in feed. Virginia says discussions with farmers in the Meeting a Sustainable Future project held following the announcement of the 190kg N/ha/year cap have drawn out advice and top tips from farmers, farm consultants and scientists on how to get rates down. Several farmers in the project group have successfully dropped nitrogen fertiliser use from more than 300kg N/ha/year to 200230kg N/ha/year but the transition has taken two to three years. A successful transition takes time and its best to do it gradually, she says. “It’s important that clover has time to re-establish and the additional nitrogen fixed - from increased clover growth - is available to the grass, to compensate for the lower nitrogen from fertiliser. “So farmers using high rates will need to start now if they want to get rates down to the target next season,” she says.
Dairy Exporter | www.nzfarmlife.co.nz | October 2020
