EXPERIMENTAL AIR-ASSISTED SPRAYING OF A MATURING CEREAL CROP UNDER CONTROLLED CONDITIONS

Outdoor tray-grown cereal plants at growth stage 39-41 were exposed to very fine/fine and medium-quality sprays from hydraulic flat-fan nozzles fitted to an air duct so that spray and air could be directed either 45 degrees forwards or vertically downwards. Spraying was done at 0.5 and 2.0 m s-1 and fluorescein deposits measured on plants and on the soil for all combinations of the above factors (24 spray options), each replicated three times. Finer sprays angled forwards and the use of air assistance interacted to increase total spray deposition on plants and reduce soil contamination. Fine sprays were better retained in the upper canopy and on stems. Forward angling increased deposits in the upper canopy but reduced penetration. A slower spray speed increased plant and soil deposition. Increasing amounts of air assistance improved plant deposits, especially in the upper canopy and on stems. Compared with 'standard' practice (a medium-quality spray, applied vertically downwards at 2 m s-1, without air assistance), forward-angled air-assisted very fine/fine and medium-quality sprays increased plant deposits on whole tillers by approximately 71 and approximately 66% and reduced soil contamination by approximately 46 and approximately 66%, respectively.