Impact of Herbicide Spray Volume Through Unmanned Aerial Vehicle on Soil Properties and Nutrient Status under Rabi Maize

Abstract

Agrochemical application using knapsack sprayers requires more time, labour, energy, and water. Agricultural drones (UAVs) offer a low-volume, uniform spraying alternative with higher spray concentration and greater operational efficiency. A field experiment conducted during the rabi seasons of 2023-24 and 2024-25 at the Water Technology Centre, PJTAU, Hyderabad, evaluated the effects of UAV-based low-volume herbicide application on soil physico-chemical properties and available nutrient status after maize harvest. The study comprised two main-plot irrigation methods, I1- surface ridge and furrow irrigation and I2- surface drip irrigation, and six subplot weed management practices: W1-W3 included varying UAV spray fluid volumes (20, 40 and 60 L ha-1); W4 was conventional knapsack spraying; and W5–W6 were checks, i.e., the weed-free and unweeded controls. The results revealed that herbicide spray volume applied via UAV and irrigation methods did not have a statistically significant effect on soil pH, electrical conductivity (EC), organic carbon (OC), and bulk density (BD) in either year. Post-harvest soil pH ranged from 7.97 to 8.11 under UAV treatments, comparable to the conventional spray (7.95-8.15) and the unweeded control (8.01-8.07). Electrical conductivity remained safe (0.31-0.36 dS m-1), confirming no salinity build-up. Soil organic carbon (0.82-0.90%) and bulk density (1.51-1.58 g cm-3) were similarly unaffected across UAV treatments. Furthermore, available nitrogen (181.23-197.90 kg ha-1), phosphorus (29.28-30.87 kg ha-1 P2O5) and potassium (308.00-331.93 kg ha-1 K2O) under UAV spray volumes showed no significant variation compared with conventional spraying. While the weed-free treatment recorded numerically higher nutrient levels due to eliminated weed-crop competition, the unweeded control exhibited lower available nutrients owing to severe weed uptake. Overall, reducing spray fluid volume via UAV technology proved safe for soil health, maintaining soil fertility while facilitating efficient weed management in rabi maize.