Reducing nutrient losses on dairy farms in The Netherlands

Abstract In the European Union, nutrient management is a topic of major political interest. The goal for nitrogen (N) is that groundwater should contain less than 50 mg nitrate/l. The general approach might result in a maximum amount of N or in a maximum number of cattle allowed per ha. However, individual countries develop alternative routes and take additional measures to deal with nutrient losses. In The Netherlands, ammonia volatilization (emission) should be reduced by 50–70% in the year 2000 compared with 1980, in addition to the European guideline for nitrate. Emphasis is placed both on phosphorus (P) and on nitrogen. Regulations limit the amount of manure (expressed in P) applied per ha. A manure (P) quotum has been allocated to each farm. A more balanced P-supply to the land has been achieved by transport of manure from surplus to deficit areas. Also lower P-contents of the concentrate feeds are stimulated. N-losses can mainly be reduced by adapting the farm operation. In this context several management practices were studied with a dairy-farm-simulation-model. A combination of a more efficient use of fertilizer N and restricted grazing in combination with a more balanced ration, resulted in considerable reductions in nitrate leaching. Application of slurry by injection techniques diminishes the ammonia volatilization at farm-level by almost 50%. Other low emission techniques, such as low emission housing and covering of slurry storages, have relatively high costs. In practice, slurry application by injection and covering of slurry storages have become obligatory. As a side effect, the odour of manure is largely eliminated from the environment as well. Application of manure to the land is only allowed in the growing season. From 1998 on, dairy farmers have to keep records of the nutrients on a nutrient balance sheet. On the basis of the nutrient balance a tax will be imposed on surplusses of N and P.