Precision UAV Spraying: Impacts of differential application rates on cotton yield

Abstract

Unmanned Aerial Vehicles (UAVs) offer a promising alternative to conventional ground-based crop management by reducing mechanical damage, soil compaction and inefficiencies in spray application. This study assessed the performance of UAV-based spraying in cotton cultivation compared to traditional hand sprayers, with emphasis on optimizing spray volumes across different crop growth stages. Since cotton crop density increases progressively, constant spray volumes can lead to wastage; therefore, three nutrient application rates (18, 25, and 30 L/ha) and three herbicide application rates (25, 37, and 50 L/ha) were evaluated. Crop growth parameters (plant height and leaf area) and remote sensing indices (NDVI and LAI) were monitored from spraying to harvest, while spray deposition was quantified using Water Sensitive Papers (WSP). The highest yield (205.2 kg) was recorded with 50 L/ha herbicide and 30 L/ha nutrient application. Remote sensing data and growth parameters indicated uniform crop health up to 40 days after sowing (DAS). Beyond this stage, 25 L/ha nutrient application was optimal until 80 DAS, while 30 L/ha was most effective from 80 to 150 DAS due to increased crop density. Overall, the findings demonstrate that UAV spraying enhances yield and efficiency by tailoring application volumes to crop growth stages, with effective post-emergent weed control being critical to maximizing cotton productivity.