Optimization of specific spray volume for spray application in pomegranate orchard using response surface methodology

Conventional air-blast sprayer applies chemical at a constant rate without any consideration to canopy characteristics, which results in excessive application of chemicals. The variable rate spraying system allows farmers to tailor the application of chemicals based on the specific requirement of the crop and results in reduced loss of chemical to environment. However, there is a lack of accurate and useful criteria for regulating spray volume according to the canopy characteristics. Therefore, a variable rate sprayer was developed and tested to optimize the spray volume to be applied in relation to canopy volume (i.e. specific spray volume) for pomegranate orchard. The experiments were conducted to optimize specific spray volume in three pomegranate orchards (cv. Bhagwa) of 2, 4 and 8 years old having average canopy volume per tree of 4.70, 7.73 and 9.61 m3, respectively, two spray control parameters i.e. nozzle flow rate (1.6, 2.1, 2.6 L min− 1) and forward speed (0.43, 0.71, 0.95 m s− 1) under field standardized conditions. According to the ANOVA results, both the nozzle flow rate and forward speed had a significant effect (p < 0.01) on Spray coverage, Droplet density and Spray deposit. The response surface (RSM) technique was applied to optimize specific spray volume by using Design Expert software. The highest spray coverage, droplet density, and spray deposit were observed at higher nozzle flow rate and at lower forward speed and vice versa. Overall, spray coverage, droplet density and spray deposit were observed to be lower at inner canopy zone than the outer canopy zone. Based on the numerical optimization, specific spray volume was observed in the range of 0.077–0.093 L m− 3 for spraying 2–8 years old pomegranate orchards for the optimal spraying. Additionally, reduction in spray volume was observed in the range of 50.2–60.1, 37.6–44.7 and 38.1–43.4% for orchard I, orchard II, orchard III, respectively.