Abstract
Development of the Hungarian ecological systems model 4M was initiated because the conditions and methods of Hungarian applications are different from the ones that appear in international crop simulation software packages. Because the majority of ecological systems models, just like the CERES model that was used during the development of 4M, do not have phosphorus and potassium modules, 4M initially was incomplete. Based on the work of Hungarian and foreign experts, a nutrient module was developed and was incorporated into the 4M model. The new module was calibrated and validated for phosphorus and potassium using the results of Hungarian aftereffects and long-term experiments. In principle, the nutrient module can be made suitable for simulating the turnover of any kind of nutrient by giving adequate values to the parameters.
Acknowledgments
The authors gratefully acknowledge the financial support of the Hungarian Scientific Research Foundation (OTKA K68884).