Performance evaluation of newly developed variable rate sprayer for spray deposition in guava orchard

Abstract

Application of pesticide inside orchards with conventional sprayers often results in an inefficient application as these are constant rate applicators and also the significant amount of pesticide gets lost in spaces between trees. To reduce the pesticide losses inside orchards, a variable rate sprayer was developed which sprayed only after the occurrence of the tree and according to the size of the tree. The performance of the developed variable rate sprayer was evaluated inside guava trees to quantify the spray deposition at six different plant positions. The sprayer was operated at three forward speeds (2, 3 and 4 km/h) with four air velocity levels (20, 25, 30 and 35 m/s) and two different types of nozzles (hollow cone and flat fan nozzle). The observed data was statistically analyzed to study the significance of selected parameters on spray deposition. The spray deposition was found to significantly increase with the increase in air velocity and hollow cone nozzle was able to deposit more amount of spray as compared to flat fan nozzle. There was no significant variation was observed with different forward speeds. The maximum spray was deposited on upper leaf surface at all selected plant position. The uniform spray deposition was observed with the air velocity of 35 m/s and hollow cone nozzle. Even though the developed variable rate sprayer varied the discharge of nozzles according to tree size, it was able to deposit the adequate amount of spray at all selected plant positions.

Opportunities and Possibilities of Developing an Advanced Precision Spraying System for Tree Fruits

“…Several studies have analyzed the effect of forward speed on spray deposition and drift [ 93 , 133 ]. Salyani [ 134 ] reported an inverse relationship between deposition and travel speed, and deposit uniformity and travel speed.…”

“…Salyani [ 134 ] reported an inverse relationship between deposition and travel speed, and deposit uniformity and travel speed. Others reported a non-significant effect of travel speed on spray deposition for variable-rate sprayers using ultrasonic sensors for canopy detection [ 93 , 111 , 135 ], although the uniformity of deposition decreased as the speed increased due to bent and distortion of air-jet [ 133 ]. Whitney et al [ 136 ] reported an enhanced deposition on the upper leaf surface with increasing forward speed of air blast sprayers in citrus, but no significant increase in the deposition was reported on the lower leaf surface.…”

“…Increasing the distance between the sprayer and the target canopy resulted in decreased deposition levels in trees. Wandkar et al [ 133 ] reported that deposition on guava trees was significantly affected by canopy depths at different travel speeds. This was due to the position of the canopies of the trees, with maximum spray deposited on the upper leaf surface.…”

“…Pergher and Gubiani [ 143 ] reported a high spray deposition (54–57%) in vineyards with a combination of lower air flow rate and lower spray volume. Wandkar et al [ 133 ] reported that spray deposition increases with increasing air jet velocity in the dense canopy, while Van de Zande et al [ 144 ] reported higher losses to deposition on the ground with air-assisted sprayers as compared to conventional boom sprayers.…”

“…Spray nozzles should be selected by following the required spray volume [ 143 ], nozzle type, and pressure [ 145 ] to improve the coverage and penetration into the canopy. Wandkar et al [ 133 ] compared two different spray nozzles (hollow cone and flat fan nozzles) and concluded that the nozzle with smaller droplet size (hollow cone nozzle) shows higher deposition. Studies conducted by Zhu et al [ 146 ] reported a higher spray deposition on the lower part of the canopy due to a greater percentage of large size droplets produced by the air-assisted nozzle as compared to hollow-cone nozzles, while [ 145 ] conducted a field study using a crossflow orchard sprayer and reported the drift reduction from air-inclusion nozzles compared to hollow-cone nozzles is significant beyond 8 meters from the last row of the orchard.…”