NITRATE LEACHING FROM AGRICULTURAL SOILS - ECOLOGICAL MODELING UNDER DIFFERENT ECONOMIC-CONSTRAINTS

Excess use of fertilizer-N results in leaching of nitrate, which threa tens the environment in various ways. Taxes on nitrogen fertilizers ha ve been suggested as a measure to reduce the nitrogen load to the envi ronment. An economic model for predicting the farmers' decisions regar ding fertilizer application, and an ecological model which predicts th e nitrate leaching given these decisions is presented. From economic t heory it is known that the economic optimal amount of fertilizer is wh ere the value of the marginal product equals the input factor price. M arginal yields are derived from the estimated yield curves and fertili zer-N levels which maximize farmers' profits. Based on the economic mo dels' predictions of the profit-maximizing fertilization practice, nit rate losses were predicted by the SOIL-SOILN model. High N-tax levels (> 200%) are needed to affect the nitrate leaching significantly. Howe ver, lower taxes may have an indirect effect on the ecology of farmlan ds by improving the economics of other measures against nitrogen losse s.