In the past decades farming has more and more become a matter of highly specialised agricultural farming systems. A negative side-issue of these new farming systems is the increase of nutrient losses to the environment, e.g. nitrate leaching to the groundwater. A more sustainable farming option can be a revival of mixed farming systems. To evaluate this alternative on the Ir. A. P. Minderhoudhoeve (APM), fertiliser scenarios of slurry and of inorganic fertiliser were examined and compared for a mixed integrated farming system.
WAVE, an integrated soil-crop model is used in this study to compare quantified analyses of slurry and inorganic fertiliser, taking the EU nitrate guideline into account. To be able to draw adequate conclusions model input data should be valid and available. This was not always the case. In order to prevent erroneous output the model should be calibrated and validated extensively. If model parameterisation is not carried out thoroughly, sensitivity of certain parameters in WAVE, such as the average distance root surface – soil solution (RD0), can lead to enormous errors.
An error was found in the model concept of WAVE, yielding incorrect growth of the wheat crops resulting in an overestimation of crop yield. Unfortunately it was not possible to solve this source code error within the time period of this study.
After calibrating and validating the model using a sensitivity analysis, fertiliser scenarios were chosen and run for three crops; maize, potato and sugar beet. Since APM slurry is said to have a higher C/N ratio than conventional slurry, scenarios with application of 100% APM slurry, 100% conventional slurry, 100% inorganic fertiliser, 50% APM slurry – 50% inorganic fertiliser or no fertilisation at all were examined. The nitrogen balances for the five fertiliser scenarios show no significant differences. Uncertainties in model input, partly due to insufficient calibration/validation, might result in unreliable output. This can also be seen in unexpected, almost identical crop yields. The nitrate leaching values of all scenarios exceed the EU nitrate guideline of 50 mg NO3 per litre groundwater immensely. Taking imperfections of WAVE into account, fertiliser practices at the APM do not perform within EU guidelines yet.
To be able to use the model WAVE more optimally for fertiliser use analysis at the APM in the future, all data collected at the APM carried out should be centrally stored. This makes the data more easily accessible for future users. Also the establishment of a general information point on changes and superable problems of WAVE will enhance the reliability and correctness of the model.