Valuing the environment in crop profitability: a case study of the Kempen, Belgium

Abstract

The limits for NO3-N concentrations in groundwater and surface waters are still under discussion, but it is likely that they will become stricter. The process of denitrification is important in preventing high agriculture-source nitrate loads from entering and polluting rivers. The aim of the research was to examine if the NO3-N concentration in drain water of agricultural fields can be kept below the EU limit of 11.3 mg l-1 by controlling the denitrification process through management of the water table level. As such the research focused on the determination of the exact denitrification amount to achieve both, limitation of the NO3-N leaching and optimisation of the nitrogen-nitrate uptake by the crop. The method used in this study is based on the nitrogen version of DRAINMOD model. This model was used to simulate the performance of the drainage system using two drainage strategies (conventional and controlled) at the Hooibeekhoeve experiment, situated in the sandy region of the Kempen (Belgium), and this for a 14-year (1985-1998) period. In the analysis a continuous cropping with maize was assumed. Daily NO3-N losses were predicted for a range of drain spacings. The study illustrated that the denitrification process has a very strong impact on the amount of nitrate that can be leached to ground and surface waters. Simulated results indicated that NO3-N losses to the environment could be substantially reduced by reducing the drainage density below the level required for maximum profits based on grain sales. The results have also shown that if the water table elevation is properly controlled, one should be able to strike the delicate balance between our need for maximum yield production and a minimum hazard to our environment. The study concluded that, if the environmental objective is of equal or greater importance than profits, the drainage systems can be designed and managed to reduce NO3-N losses while still providing an acceptable profit.