Comparison of ground and aerial defoliant and growth regulator applications in cotton (Gossypium hirsutum L.) using a traditional ground spraying system vs. an aerial drone

Abstract

Cotton has historically been a significant economic product both in Greece and worldwide, driving major developments in agriculture and industry. It was a key factor in the 19th-century American economic expansion, incentivizing extensive production growth. Throughout history, persistent challenges in cotton cultivation have spurred innovations and technological advancements. In recent years, the climate and energy crises, coupled with the need for sustainable and optimized cultivation practices, have highlighted the importance of reducing production costs. This has brought the use of spraying drones to the forefront of cotton farming. Environmental awareness and market demand for sustainable production, alongside chronic issues with plantation damage from conventional sprayers (particularly during advanced growth stages), have underscored the advantages of spraying drones. These drones offer precision in application, reduce the use of spray liquids, and minimize crop damage. Defoliation, which requires precise spraying to avoid economic losses due to weather or damage from conventional equipment, is an area where drones have provided significant solutions. Consequently, spraying drones, along with related precision agriculture technologies such as satellite data and on-the-go sensors, are becoming integral to modern cotton cultivation, enabling variable rate spraying. However, there is still ambiguity regarding the flight parameters, dosage, and financial implications of drone sprayers compared to conventional methods. This study aimed to compare the effectiveness of aerial RPAAS/UAS sprays with traditional ground-based sprayers, focusing on recommended dosages and operational factors. It assessed droplet distribution, defoliation timing and quality, and efficiency in saving spray liquid and time. The experimental farm was divided into four equal sections (0.55 ha each), with consistent cultivation practices applied throughout. The study tested four different spraying methods: 100% of the recommended dose (ethephon 48%, carfentrazone-ethyl 24%) with a conventional sprayer, 15% of the recommended dose with RPAAS/UAS, 50% of the recommended dose with RPAAS/UAS, and 100% of the recommended dose with RPAAS/UAS. Statistical and ROI analyses were conducted to evaluate economic feasibility and potential profit enhancement for farmers. The use of UAS/RPAAS for applying harvest aids significantly reduced production costs and increased efficiency. Drone-treated plots showed higher ROI than conventional methods. Notably, Drone Plot 2, using 50% of the standard dose, achieved more than double the ROI of the control, offering a sustainable solution with savings and increased production. Drone Plot 1, intended to fully replace conventional methods, demonstrated high ROI but posed risks under adverse weather due to longer defoliation times. Despite these risks, its high fiber-specific gravity and much lower cost indicate its potential under certain conditions. Drone Plot 3, using the recommended dose, confirmed the effectiveness of UAS/RPAAS, yielding higher ROI and reducing production costs. Spraying drones supports economic viability, increases profits, and reduces chemical usage, promoting sustainability.