The relations of leaf area index with the spray quality and efficacy of cotton defoliant spraying using unmanned aerial systems (UASs)

Leaf area index influences on the spray quality and efficacy, and has relationships with the spray quality and efficacy in agricultural spray application. The aim of the present study was to sought the relations of LAI with the spray quality and efficacy of cotton defoliant spraying using unmanned aerial systems (UASs). A TRAC-II instrument was used to measure the LAI of cotton plants. Three different types of UASs with different spray volume rates (48 L·ha−1, 72 L·ha−1 and 96 L·ha−1), flight altitudes (1.5 m, 2.0 m and 2.5 m), and flight speeds (1 m·s−1, 2 m·s−1 and 3 m·s−1) were tested. Results showed the following: (1) There were exponential relationships between LAI and droplet deposition at volume rates of 48 L·ha−1, 72 L·ha−1 and 96 L·ha−1. There were cubic relationships between LAI and cotton defoliation rate at volume rates of 48 L·ha−1, 72 L·ha−1 and 96 L·ha−1. (2) The multiple regression model between LAI and volume rate, and droplet deposition was D = −0.02896 − 0.08055 L + 0.01226 V, the R2 and RMSE values of the training and test sets were 0.81 and 0.08, and 0.83 and 0.07, respectively. The multiple regression model between LAI and volume rate, and cotton defoliation was C = 100.8524 − 4.0617 L + 0.05482 V, the R2 and RMSE values of the training and test sets were 0.72 and 0.17, and 0.75 and 0.06, respectively.