Dairy farming in the Netherlands in transition towards more efficient nutrient use

In the Netherlands, agriculture as a whole is not environmentally sustainable. It contributes to the emission of greenhouse gases (~ 15%), acid rain (~ 50%) and groundwater pollution (~ 85%). The surplus of phosphate, averaged over the area of cultivated land amounting to ~40 kg P ha-1, originates ~30 and ~40% from dairy farming and pigs, respectively. Nitrogen surpluses, amounting to ~350 kg ha-1, contribute to ammonia, N2O and NO(x) volatilization and nitrate leaching, levels that exceed present and future standards. Dairy farming contributes ~ 55% of the nitrogen losses. Despite their genetic potential and advanced diet formulation, the efficiency with which animals convert nutrients into animal products remains rather low. A major part of the nutrients is excreted in faeces and urine. Hence, there is an urgent need for more sustainable nutrient management at higher hierarchical levels for production systems in WhiCh the inputs are tuned to the carrying capacity of the agro-ecosystem and the internal nutrients in animal manure, e.g. N and P, are used more efficiently. The paper discusses the effectiveness of management practices to reduce the nutrient losses, along with aspects of system behaviour. Nutrient flows of dairy farms are analysed and the most effective interventions identified to (1) maintain level of production while (2) reducing the nutrient losses to environmentally acceptable levels. Finally, results/projections of prototype experimental farms are discussed