IMPLEMENTATION OF A HERBICIDE SIMULATION-MODEL IN A GEOGRAPHICAL INFORMATION-SYSTEM WITH AN EXAMPLE OF A SITE-SPECIFIC APPLICATION

A Geographical Information System (GIS) was combined with a model for simulating leaching and degradation of herbicides. The model uses firs t-order kinetics to simulate degradation, and a cascade model to simul ate transport. This system was tested with data from a 16 km(2) resear ch catchment in northern Germany. Geometrical, topological, and soil d ata of this area were stored in a GIS. For the whole area, divided int o small homogeneous sites (ecotopes), model runs were carried out. The system is able to handle data for all ecotopes automatically and to p resent calculated results on the behaviour of herbicides as distribute d over time and depth for the area. An application of ethofumesate mad e in sugar-beet in spring and recropping of winter wheat after beet ha rvest was modelled. Degradation/sorption parameters were estimated fro m similar soils. Simulation results showed slower degradation in the s andy sites of the catchment, compared to the more loamy regions. Resid ues of herbicide remaining after beet harvest were greater than 20% of the applied dose in the sandy soils after 150 days. Hence, high risk of damage to the following crop of winter wheat was predicted. At the other sites residues remaining were between 2% and 20% of the applied dose.