TESTING SIMULATION-MODELS FOR THE ASSESSMENT OF CROP PRODUCTION AND NITRATE LEACHING IN HUNGARY

Planning alternative land-toe management requires at minimum the evalu ation of crop productivity and profitability as well as the environmen tal consequences. Crop-simulation models are one means of making the a ssessments needed for planning sustainable land use. However, the syst ems approach must be proven to represent reality in order to be accept ed by potential users. A long-term crop-rotation experiment with vario us N fertilizer applications, conducted in Nagyhorcsok, Hungary, from 1968 to 1988 provided an excellent data set to test the capability of crop-simulation models for estimating biomass production, yield and ni trate leaching. The rainfall, soil type and evaporation rates at the s ite provided a circumstance in which the nitrate leaching from the roo ting zone of wheat and maize was trapped in the sub-soil at a depth of 4-5 m. This measurable nitrate in the sub-soil because the basis for testing the simulated leaching using the CERES-wheat and CERES-Maize c rop-simulation models. The model's were locally calibrated for accurac y, in the drainage coefficient, for wheat and maize genetic coefficien ts and for solar radiation estimations from sunshine hours data, The m easured and simulated nitrate use by plants and the loss by leaching w as within acceptable limits most of the time. The biggest errors occur red in treatments without any nitrogen added The simulated and measure d results showed that when 150 kg/ha/yr or less was applied, the leach ing tvas minimized and about the same as no fertilizer. With a 250 kg/ ha/yr application, there was about 100 kg/ha/yr leached and the yields were not improved over the 150 kg/ha treatment. The measurements of t he rotation study reported herein represent less than 1% of those avai lable from a country-wide study, where soil and weather are different.