N-LES CAT (N) - Modelling tool for annual values of root zone nitrogen leaching
N-LES is an empirical model for calculation of annual values of root zone nitrogen leaching. The model comprises a combination of additive and multiplicative effects. N-LES was developed on 600 observations of annual leaching of nitrogen from the root zone from both experimental fields and fields in normal agricultural production in Denmark. The model explained 68% of the observed variation. The systematic effects included in the model are: level of total-nitrogen added in the crop rotation; fertilization in spring; autumn fertilization; nitrogen left by grazing animals; effect of ploughing-in of grass; soil type (clay- and humus-content); water percolation through the root zone, and crop type. In Denmark, percolation has been calculated by EVACROP, which comprises rather simple conceptual models for describing vegetation and for calculating the water balance. N-LES has since 1992 been used in Denmark as a tool for evaluating the effect of policy measures for combating diffuse nitrogen pollution from the agricultural production.