Comparative analysis of UAV and electric backpack sprayers for herbicide efficacy and crop-weed nutrient dynamics in direct-seeded rice

Weeds represent a significant obstacle to direct-seeded rice (DSR) cultivation by impeding crop growth and nutrient uptake. Conventional use of electric backpack sprayers (EBS) for herbicide application is labour intensive, uneven distribution, and poses health hazards. This study evaluates the efficiency of uncrewed aerial vehicles (UAVs) in weed management through herbicide application, as well as its impact on the nutrient dynamics between crops and weeds. An experiment was conducted at Tamil Nadu Agricultural University, Coimbatore, India, during the kharif (2022) and rabi (2022-2023) seasons to test the pre-emergence (PE), early post-emergence (EPOE) and post-emergence (POE) herbicides using UAVs and EBS. Single EPOE applications had limited effectiveness, resulting in higher weed biomass, reducing crop growth and 23-31% of yield loss. Plots treated with PE pretilachlor fb POE bispyribac sodium, effectively controlled broad spectrum weeds, leading to higher weed control efficiency and herbicide efficacy index. However, no significant difference was observed between the UAV and EBS methods. Nevertheless, the UAV treatment required lesser carrier volume (by 88-94%), recharging time (by 94%) and number of battery swaps (by 67%) compared to EBS treatment. Furthermore, UAV application resulted in 25-57% lower input energy compared to the EBS application. Additionally, UAV application decreased application cost, time and improved energy use efficiency and work efficiency (3.34-6.85). UAV adoption helps reduce the risk of venomous snakebites, minimize direct exposure to pesticides and lessens the overall labor burden. UAV application of herbicides, particularly the combination of PE pretilachlor fb POE bispyribac sodium effectively controlled weeds, improved nutrient uptake, energy use efficiency, work efficiency and enhanced crop growth. UAVs offer a viable alternative to conventional spraying systems for herbicide application in DSR systems. • Sequential application of herbicides significantly enhanced weed control efficiency across grasses, sedges and broad leaved weeds, regardless of the application method. • Single early-post emergence applications were less effective, leading to higher weed biomass, poor crop growth and 23-31% yield loss. • Uncrewed aerial vehicle (UAV)-based herbicide application demonstrated higher energy use efficiency and work efficiency • UAV application reduced application time, input energy, carrier volume and labour burden compared to conventional backpack application. • UAV application of pretilachlor followed by bispyribac sodium achieved superior weed control and enhanced rice growth attributes.