Phosphorus (P) management in the 'De Marke' dairy farming system

In the sandy regions of the Netherlands water quality is threatened by high losses of nutrients from intensive dairy farms. About 67% (32 kg ha(-1)yr(-1)) of farm inputs of P in purchased feeds and fertilisers do not leave in milk or cattle. The Dutch government defined decreasing maximum permitted nutrient surplusses for the period 1998-2008, at 9 kg ha(-1)yr(-1) for P. Farmers suppose that reducing the surplusses will be costly, because it limits application of slurry, which then has to be either exported or additional land has to be purchased. Moreover, farmers are worried about the impact on soil fertility and crop growth. To explore the possibilities of reducing surplusses by improved management, farming systems research is carried out at prototype farm 'De Marke'. Results indicate that average intensive dairy farms can reduce P surplus sufficiently, without the need to buy land or to export slurry. Key factors are reductions in purchased feeds (by reduced needs per kg milk as a result of a higher milk yield per cow, less young stock and judicious feeding) and fertilisers (by improved management of 'home-made' manure and an increased maize area). Initially, P fertility status of the fields of 'De Marke' decreased, but stabilised in the seventh year at a level not restrictive to crop production.