Nutrient balances in field vegetable production systems

In this review paper an overview of the nitrogen (N) and phosphorus (P) cycles in agricultural systems is presented. The information summarized provides general information on the important processes involved as they relate to losses from agricultural systems. Such background information is a prerequisite for designing management strategies to achieve a sustainable balance between reducing the environmental impact of N losses and protecting farmers' profitability. In field vegetable production most N is lost via nitrate leaching because often large amounts of nitrogen remain in the soil after harvest of the crop. This N includes residual soil mineral N and N present in crop residues. Quantitative data are presented on residual soil mineral N, N present in crop residues and nitrate leaching in field vegetable production systems. To combat too high nitrate leaching from agricultural soils the European Commission has issued the Nitrate Directive. Information on this Directive and on how the Dutch government imposed legislation to meet the demands of the Nitrate Directive is given. The project "Farming with a future" is also presented. This new project has been set up in The Netherlands to develop and test environmentally and economically sustainable field crop production systems. As an example of the first results of the project, N balances of two systems of leek production are shown.