Nutrients balance on a mountain dairy farm

From 1994 to 2003 three methods to measure the nutrients balance were compared on the dairy farm La Frêtaz (VD). Since 1994 no mineral fertilisers were applied on permanent grassland. At the whole farm level the difference between nutrients inputs and outputs was null or positive for nitrogen (N), phosphorus (P), potassium (K) and magnesium. Both methods comparing the plant requirements to the estimated or measured nutrients supply indicate a small deficit for N and P. The official method used in Switzerland until 2002 (AEF), which relies on an estimation of the nutrients supplied by livestock, leads to the highest deficits: -19 kg N/ha/year and – 3 kg P/ha/year. All three methods show an excess of potassium. The surplus was much higher with the AEF approach than with the method taking into account the nutrients really supplied by the fertilizers. This means that the norm for K excretion by cattle is too high for the dairy farm La Frêtaz. On the whole, though the results differ according to the method and the nutrient, the risks of environment enrichment are small.