Quantifying dairy farm nutrient fluxes and balances for improved assessment of environmental performance

Abstract

Excess nutrients are challenging the long-term sustainability of grazing-based dairy farming. Whole-farm nutrient-mass balance (NMB) is a well recognised approach to improve on-farm nutrient management decisions. In the present paper, we use a standardised approach for quantifying NMB on grazing-based dairy farms, using a newly developed online tool. Preliminary evaluation, using selected farm data from a previous Australia-wide dairy-farm nutrient study, demonstrated highly comparable estimates of farm area, nutrient fluxes and NMB, with substantial efficiencies in time and sample analysis. Nutrient mass balances were also determined on 16 diverse dairy farms across the five major dairy regions of Victoria, Australia. These results highlighted the importance of purchased feed, fertiliser and milk sales, as major sources of nutrient inputs and outputs, with whole-farm NMB for the 16 dairy farms ranging from 185 to 481 kg/ha for nitrogen, 12–59 kg/ha for phosphorus, 9–244 kg/ha for potassium and –6–55 kg/ha for sulfur. Current industry adoption of the NMB tool has confirmed the benefits of a standardised and efficient collation and processing of readily available farm data to inform nutrient management decisions on commercial dairy farms. We suggest that the standardised assessment of nutrient fluxes, balances and efficiency, as well as feed- and milk-production performance at the whole-farm level, provides dairy farmers, farm advisors and industry and policy analysts with the ability to determine industry-wide goals and improve environmental performance.