Research Progress on Intelligent Variable-Rate Spray Technology for Precision Agriculture

Conventional continuous pesticide application remains prevalent in agriculture, but its limitations in addressing the spatial–temporal variability of biotic stressors have led to excessive chemical inputs and inefficiency. The emergence of precision agriculture has catalyzed significant advancements in variable-rate spray systems to optimize agrochemical deployment through real-time modulation. This technology demonstrates critical advantages in minimizing the environmental footprint while maintaining crop protection efficacy. Our systematic review analyzes three foundational variable-rate spray architectures—pressure-regulated, flow rate-regulated, and pesticide concentration-regulated mechanisms—evaluating their maturity and implementation paradigms. Pressure-regulated technology relies on the pressure–flow relationship to achieve regulation, but there is a narrow range in flow regulation, atomization stability is insufficient, and there are other defects. Flow rate-regulated technology achieves precise control through the dynamic adjustment of the nozzle orifice area or Pulse-Width Modulation duty cycles, but this technology faces mechanical wear, a nonlinear flow–duty cycle relationship, and other challenges. Pesticide concentration-regulated technology is centered on real-time mixing, which can avoid the residue of chemicals but is highly dependent on fluid characteristics and mixing efficiency. This study proposes improvement paths from the perspectives of hardware optimization, control strategy integration, and material innovation. Through the summary and analysis of this paper, we hope to provide valuable references for future research on variable-rate spray technology.