Efficient resource management in dairy farming on peat and heavy clay soils

Peat and heavy clay soils in the Netherlands are mainly used for permanent grassland to support dairy farming. As a result of intensification in dairy farming during the last decades, environmental quality is threatened by high emissions of N and P. Increased drainage of the wet soils has induced high mineralization rates, with associated losses of organic matter and nutrients. Improved utilization of N and P sources and new grazing and feeding strategies are proposed to reach environmental targets without loss of production. A sustainable prototype-system is designed by stepwise theoretical improvements of the current dairy farm, Although groundwater levels are kept high to limit breakdown of soil organic matter, the high availability of N and P from unavoidable peat mineralization offers the possibility to drastically reduce fertilizer inputs, which will directly reduce nutrient losses to the environment. Reduction of protein content in the ration reduces ammonia emission by approximately 20%, while milk production levels of 14,000 kg ha(-1) per year can be maintained. The change from full to restricted grazing effectively reduces N losses from soil, but ammonia emission reductions are only significant with an improved slurry-application technique. A reduction in young stock reduces the roughage requirements but contributes little to the reduction of the nutrient surplus. Reduction of N imports trades off with the restoration of the soil-N stock, which is depleted by mineralization and unavoidable losses. Optimization of the utilization of nutrient resources is an effective first step to realize a sustainable farming system.