Limits to intensity of milk production in sandy areas in The Netherlands

Agricultural land in sandy areas is mainly in use by dairy farms. As a result of intensive fertilisation and irrigation, environmental quality is threatened by lost nutrients and lowered groundwater levels. Therefore, Dutch government put decreasing limits to losses of nutrients, with lowest values for well-drained sandy soils. Besides, use of groundwater for irrigation will be restricted. Reducing milk production per hectare can be effective to reduce nutrient losses but is costly, as is the increase of output of nutrients by exporting manure. Improved resource management, leading to reduced inputs per kg milk, might be a more attractive option to realise both environmental and economic goals. This paper describes a procedure to quantify the impact of management on the limits of milk production per hectare on well-drained sandy soils, at defined maximum levels of permitted nutrient losses. The procedure has been applied to a range of farming systems, in order of increasing complexity of nutrient management. It is concluded that current average milk production intensity (12,400 kg ha-1 yr-1) has to be reduced drastically if farm management is not successful in increasing the conversion of dietary N (into milk and body weight) and the re-use of N in manure. On the other hand, results suggest that an intensity of almost 15,000 kg ha-1 yr-1 should be attainable by best farmers