MODELING SPRAY DRIFT FROM BOOM SPRAYERS

A random-walk model, IDEFICS, is described to compute downwind spray d rift from conventional boom sprayers in chemical crop protection. Spra y deposits are computed downwind from the sprayed crop field. The mode l basically is two-dimensional (2D), but close to the spray nozzle the model is 3D, incorporating driving speed and entrained air-currents b elow the nozzle. Input parameters are related to the geometry of the f ield, to the boom sprayer settings and to environmental factors. The m odel was calibrated with a set of held trials using an experimental si ngle-nozzle sprayer in a cross wind. In the trials, tap water containi ng a fluorescent dye was used as the spraying liquid, and downwind dep osits were measured by fluorimetry. Variations of boom height, spray n ozzle size, driving speed and liquid pressure were examined, at varyin g wind speeds. Both experiments and simulations showed that boom heigh t, wind speed and nozzle size were the major factors affecting spray d rift. Surprisingly, liquid pressure did not affect downwind spray depo sits at all. A comparison between model results and results of a pract ical field trial showed a good agreement if field trials were averaged over several replications. The variation between individual replicati ons is however too large to use single trials for model verification. Further calibration trials are needed to investigate the effect on dri ft of multi-nozzle arrangements, crop height and medium-and coarse-siz ed spray nozzles. (C) 1997 Elsevier Science B.V.