EXPERIMENTAL AIR-ASSISTED SPRAYING OF YOUNG CEREAL PLANTS UNDER CONTROLLED CONDITIONS

Cereal plants grown in trays outdoors were sprayed indoors, at the four-leaf stage, with and without air assistance from a commercial air-curtain device fitted with an electrically driven cross-flow fan. Flat-fan hydraulic pressure nozzles producing very fine/fine and medium spray qualities were fitted to the air duct so that they and the air curtain could be directed either 45 degrees forwards or 45 degrees backwards, relative to the direction of travel, as well as vertically downwards. Spraying was done at 0.5, 1.0 and 2.0 m s-1 and fluorescein deposits were measured on the plants and soil for all combinations of the above factors (36 spray options), each replicated three times. Analysis of deposits measured by spectrofluorimetry showed that fine-quality sprays produced larger plant deposits than medium-quality sprays and that angling the spray trajectory, especially 45 degrees forwards, also substantially increased deposition. Forward angling was superior to the backward trajectory. Air assistance further increased the amount of spray retained, and reduced deposits on the soil. An increase in plant deposits of approximately 74% was recorded for finer sprays angled forwards with air assistance compared with a medium-quality spray applied vertically without air assistance at a spray speed of 2 m s-1. At the slowest spray speed (0.5 m s-1) both spray qualities angled forwards with air assistance increased deposition by approximately 110% compared with a mean deposition increase of approximately 75% without air assistance. Air assistance substantially reduced (approximately 70%) spray drift in a wind tunnel at a wind speed of 4 m s-1, but significantly increased the small amounts of drift measured in winds of 1.0 and 2.0 m s-1.