The Effect of Diet and Farm Management on N 2 O Emissions from Dairy Farms Estimated from Farm Data

The N 2 O emissions of 21 dairy farms in Germany were evaluated to determine the feasibility of an estimation of emissions from farm data and the effects of the farm management, along with possible mitigation strategies. Emissions due to the application of different fertilisers, manure storage and grazing were calculated based on equations from the IPCC (Intergovernmental Panel of Climate Change) and German emission inventory. The dependence of the N 2 O emissions on fertiliser type and quantity, cultivated crops and diet composition was assessed via correlation analysis and linear regression. The N 2 O emissions ranged between 0.11 and 0.29 kg CO 2eq per kilogram energy-corrected milk, with on average 60% resulting from fertilisation and less than 30% from fertiliser storage and field applications. The total emissions had a high dependence on the diet composition; in particular, on the grass/maize ratio and the protein content of the animal diet, as well as from the manure management. A linear model for the prediction of the N 2 O emissions based on the diet composition and the fertilisation reached a predictive power of R 2 = 0.89. As a possible mitigation strategy, the substitution of slurry for solid manure would reduce N 2 O emissions by 40%. Feeding cows maize-based diets instead of grass-based diets could reduce them by 14%.