Nitrogen use efficiency indicators designed for the diversity of global dairy production systems

Whole-farm nitrogen (N) budgets are determined to derive N use efficiency (NUE) and N balance estimates, useful for assessing the risk of N losses for dairy production systems. Component-based N indicators, applicable for the cycling of N through the soil, pasture/crop, animal product and excreta continuum, provide greater insights into key N fluxes and transformations impacting N recovery and farm productivity, leading to improved management. However, methods for calculating and utilising these indicators for the diversity of dairy systems globally are often inconsistent. This paper reports on the development of N efficiency metrics which ensure an appropriate framework for international reporting and interpreting.

Global milk output in 2018, estimated at 843 million tonnes, ranks among the top five agricultural commodities and follows a long-term growth trend (~2% p.a.). On-going production gains result from higher dairy herd numbers and increased yield per cow, along with improvements to milk collection processes (FAO 2019). Milk animals are raised in a variety of production systems which can be categorised as: specialized landless systems, market-oriented dairy-crop systems, subsistence-oriented dairy-crop systems, and pastoral grazing-based systems. Of the 133 million holdings keeping dairy cattle, many farmers in developing countries keep herds of only 2 – 3 head, while in industrialised economies, herds are generally much larger. Farms with more than 100 cows represent less than 0.3% of all dairy farms globally.