The risk of nitrate leaching is higher in field vegetable production than in arable crops or grassland. Different species of vegetables have different leaching potentials, which can be reduced through appropriate management.
Nitrate leaching into groundwater adversely affects drinking-water quality. Excessively high nitrate concentrations have been measured in a number of spring catchments and groundwater pumping stations in Switzerland. Moreover, leached nitrate can enter the Rhine, and hence the North Sea, via groundwater and watercourses. There, it contributes to coastal water eutrophication. Nitrogen (N) is often the limiting nutrient for algae growth on the North Sea coast.
Vegetable Species and their Nitrate Leaching Potential
More nitrate is leached per area in field vegetable production than under arable crops or grassland. Through a study of the literature, vegetable species were classified according to their nitrate leaching potential and management measures for reducing nitrate leaching were evaluated.
The leaching potential of 40 vegetable species was classified on the basis of values cited in the literature for N-fertiliser requirement, amounts of N in crop residues, and rooting depth. Whereas cabbage species have a high potential, the leaching risk for most leafy vegetable species was rated as low. Leaching could be reduced in particular by controlling irrigation, by a more accurate calculation of the N-fertiliser requirement, through the increased integration of cover crops in crop rotations, and through optimised crop residue management. Fertilisation, tillage and crop residue management are the farming practices with the most significant research requirement.
The consistent application and further development of four measures can reduce undesirable nitrate leaching in field vegetable production, thereby reducing groundwater pollution.
- Irrigation control: Appropriate irrigation reduces leaching risk and ensures a water supply with the best possible nutrient uptake.
- Improved calculation of N-fertiliser requirement: Plant-available nitrogen present in the soil should also be taken into account when assessing N fertilisation.
- More-environmentally-friendly crop rotations via the integration of cover crops: Cover crops absorb water and nitrogen from the soil, thus reducing leachate formation and nitrate concentration in the leachate.
- Optimisation of crop residue management: Nitrogen losses from plant material remaining in situ should be reduced. The removal of N-rich crop residues from the field could be a promising approach.