Nitrogen (N) surplus is the balance between Nitrogen inputs and Nitrogen outputs.
In OverseerFM N Surplus is calculated as the sum of the nitrogen inputs used for production on the farm (eg fertiliser, imported feed, irrigation water & clover fixation) minus the total nitrogen that is removed from the farm as products (eg meat, wool, milk, crops, exported effluent, supplements sold or stored).
N surplus is an indicator of how efficiently the farming system is using nitrogen. The lower the N surplus number, the more efficiently N is being used in the system.
Where farms are utilising the N fixing capacity of legumes in their system, the OverseerFM N surplus number is a more useful metric for understanding the efficiency of that system than the sometimes used “purchased N surplus” which does not take account of N fixed by clover.
N surplus is reported in OverseerFM in the Farm Details report and in the Benchmarking by Farms reporting for Farm Groups
N Surplus does not account for the environmental conditions of a farm which are important factors in understanding N-leaching risks. These risks can be assessed through analysis of the block and farm nutrient budgets.