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

Cereal plants grown in trays outdoors were sprayed indoors, at the fou r-leaf stage, with and without air assistance from a commercial air-cu rtain device fitted with an electrically driven cross-flow fan. Flat-f an hydraulic pressure nozzles producing very fine/fine and medium spra y qualities were fitted to the air duct so that they and the air curta in could be directed either 45 degrees forwards or 45 degrees backward s, relative to the direction of travel, as well as vertically downward s. Spraying was done at 0.5, 1.0 and 2.0 m s-1 and fluorescein deposit s were measured on the plants and soil for all combinations of the abo ve factors (36 spray options), each replicated three times. Analysis o f deposits measured by spectrofluorimetry showed that fine-quality spr ays produced larger plant deposits than medium-quality sprays and that angling the spray trajectory, especially 45 degrees forwards, also su bstantially increased deposition. Forward angling was superior to the backward trajectory. Air assistance further increased the amount of sp ray retained, and reduced deposits on the soil. An increase in plant d eposits of approximately 74% was recorded for finer sprays angled forw ards 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 w ith air assistance increased deposition by approximately 110% compared with a mean deposition increase of approximately 75% without air assi stance. 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.