Stickstoffeffizienz von Milchviehbetrieben

Nitrogen (N) efficiency on farm gate is studied for 2010 on ten Norwegian, organic dairy farms and ten conventional as references. Preliminary results are presented here, and the method is discussed. N-efficiency is calculated as Net N-Export (kg) / Net N-Import (kg). Nitrogen from biological N-fixation had a large impact on calculated N-efficiency. Because of large yearly variations and very uncertain estimates of amount of N from biological N-fixation caused by uncertainties in roughage yields, clover content and the amount of nitrogen fixed per kg clover harvested, the numeric values on estimated N-efficiency should not be taken as exact values. N-efficiency is estimated with and without biological N fixation. There are large variations in farm size, use of concentrates and milk yield per cow within the group of organic farms. However the variation is even larger within the conventional farms'. On average the estimated N-efficiency were higher on the organic than on the conventional farms. However, there are large variations in estimated N-efficiency within the organic as well as the conventional group. This gives us the possibility to identify on which farms actions should be taken to improve N-efficiency.