USING A GEOGRAPHIC INFORMATION-SYSTEM (GIS) FOR HERBICIDE MANAGEMENT

An algorithm was developed for use in a geographic information system (GIS) to model the surface movement of herbicide in response to a rain fall event as modulated by slope, soil, management practices,and time of herbicide application. This algorithm was implemented in the GIS so ftware Geographic Resource Analysis Support System (GRASS) and uses as submodeIs the Natural Resources Conservation Service (NRCS) curve num ber procedure, the Universal Soil Loss Equation (USLE), and the pestic ide submodel from the model Chemicals, Runoff, and Erosion from Agricu ltural Management Systems (CREAMS). The algorithm estimates the loss o f pesticide from field areas, runoff flow patterns, and the accumulati on of pesticide downslope in response to a rainfall event. The simulat ed movement of atrazine, cyanazine, and alachlor was studied under hyp othetical management scenarios in the Lake Pittsfield watershed in Pik e Co., IL, Tillage for the simulation was by moldboard plow. An altern ate no-till scenario was simulated to test tillage effect on atrazine movement. Herbicides were applied either PPI, PRE, POST, or early prep lant for no-till (treated as same application time as PPI but without incorporation), The experiment was designed to incorporate timing of a pplication as a management factor from the standpoint of a single rain event on May 16, The results used for comparison were data from 1 d a fter POST application, 15 d after PRE application and 30 d after PPI a pplication. The algorithm showed that areas of greater herbicide risk can be located within a watershed and that the effect of alternative m anagement practices can be evaluated using a GIS.