A FEASIBILITY STUDY OF DIRECT-INJECTION FOR VARIABLE-RATE HERBICIDE APPLICATION

Variable-rate application of herbicides based on soil properties and c rop yield potential may be a viable approach to reducing the quantitie s of herbicides used in crop production. Application accuracy of direc t injection equipment is an important issue for variable-rate applicat ion. A simulation model was developed using SLAM II to assess the perf ormance of a direct injection sprayer used for site-specific applicati on of preemergence herbicides in corn. Field data from a university re search farm were used as input to the model (i.e., soil texture, organ ic matter content, and yield potential). Several factors such as in-li ne mixing location, hose diameter nozzle spacing and size, and ground speed were investigated for their effects on system performance. A com plement of system parameters was identified to reduce application erro rs. Multiple system errors were combined using the mean square error a pproach. Results of the simulation were input to a GIS software to gen erate herbicide application rate maps and the corresponding error rate maps. Application errors for direct injection systems were as high as 40% for mistreated areas of the field, with changes in chemical conce ntration at the remote nozzles occurring after as much as 80 m of trav el past the point of a step change of the input command to the control ler: Recommendations for reducing delay times at the nozzle include mo ving the in-line mixing location close to the boom and using smaller l ine sizes to reduce line volume, without appreciably increasing pressu re drop.