A comparison of a simple bluff plate and axial fans for air-assisted, high-speed, low-volume spray application to wheat and sunflower plants

Abstract

Two different systems, mounted together on a single spray vehicle, were compared for high-speed (20–40 km/h), low-volume (11–15 l/ha), air-assisted spray application to wheat and sunflower plants, using fluorescent pigments. In the first system, a simple bluff plate (a vertically mounted, long rectangular metal plate) in front of the nozzles, was used. The second system consisted of four spray heads, composed of a rotary sleeve atomizer in the centre of a shrouded axial fan, so that the spray was entrained in a directed air stream. The rotary sleeve atomizers were used with both systems, the axial fans being removed from the spray heads for bluff plate only treatments. Treatments compared were: bluff plate plus rotary sleeve atomizers, axial fans plus rotary sleeve atomizers, rotary sleeve atomizers only with no air assistance, and bluff plate plus axial fans together (with rotary sleeve atomizers). Deposits in all treatments were compared with those obtained using a conventional (non-air assisted) fan jet spray boom, using conventional spraying speeds (7–10 km/h) and spray volumes (about 100 l/ha). The axial fans used made little difference to the spray deposits obtained when compared to the non-air-assisted treatments. They also gave no additional advantages when used in combination with the bluff plate. Hence it was concluded that axial fans are of little value for improving spray deposition in high-speed, low-volume, spray application in field crops. However, air-assisted spraying with a simple bluff plate, when compared to the non-air-asssisted treatments, increased pigment deposits by about four times on 0·5 m tall wheat plants and by about 2·5 times on 0·5 m tall sunflower plants. On sunflowers using the bluff plate, about 60% of the spray was deposited on lower leaf surfaces, whereas without the bluff plate and with a conventional boom, little or no spray was deposited on lower leaf surfaces. Compared to a conventional fan jet boom, deposits with the bluff plate plus rotary sleeve atomizers were about 2·5 times higher on wheat and about 10% higher on sunflowers. Bluff plates are simple, cheap and reliable, with no moving parts, whereas axial fans are complex, expensive and high in power requirement by comparison. It was concluded that bluff plates warrant further investigation for their potential in high-speed air-assisted spraying of field crops, whereas axial fans are of little or no value for this purpose.