Optimising on-farm nitrogen management in the face of regulated fertiliser input

The key purpose of this project was to investigate how farmers had responded to the regulatory capping of synthetic nitrogen fertiliser at a maximum of 190 kg N/ha onto pastoral farms, and the impact this had had on nitrogen leaching and greenhouse gas emissions.

The analysis was carried out on 12 irrigated Canterbury and 3 Southland dairy farms.

The analysis shows that the impact of the restriction on synthetic nitrogen fertiliser application has seen all farms in the study reduce applications to (in most cases) well below the 190kg/ha limit. The amount of total nitrogen input into the system had also reduced, but much less due to “compensatory” inputs in the form of increased supplementary feeds and increased cropping, and in particular an increase in nitrogen fixation by clovers. Overall, total nitrogen within the system reduced by 9% on average for the Canterbury farms studied, and 18% for the Southland farms.