Management strategies to reduce nutrient losses from vegetable crops

Recent reviews have outlined the potential environmental risks associated with growing field vegetable crops. These often arise when fertiliser is applied in excess of crop demand, leaving unused fertiliser in the soil at harvest. Other risks are associated with how much of the crop is removed from the field after harvest; for some crops, such as sprouts, over 70% of the crop remains. If not managed correctly, this excess N can lead to excessive nitrate levels in groundwater, and eutrophication in inland waters. It can also lead to excessive levels of nitrate in the leaves of crops, particularly spinach and lettuce. In order to protect the environment and our health the EU has instituted directives to provide maximum levels of nitrate in drinking water and food. It is our job to provide the horticultural industry and government policy makers with guidelines for profitable methods of field vegetable production that will not pollute the environment. The guidelines also need to be based on sound scientific principles and yet sufficiently practical to be used at farm and field level. In order to achieve these aims we need to understand what's going on in the soil, the atmosphere, the plant, and the interactions between them. We need to be able to estimate crop demand for nitrogen, when that nitrogen is needed by the crop, and how the structure of the crop root system could affect its recovery. There are many potential strategies that can be used to reduce nitrogen losses from field vegetable crops, but not all of them will be relevant or effective in all situations. The trick will be to integrate our knowledge of what we know about crops and soils and be able to apply it to make site specific recommendations.