Progress in foreign agricultural aviation electrostatic spray technologies and references for China

Abstract: Chemical pesticide residues have posed a great impact on crops and the ecological environment in recent years, as the prevention and control of crop diseases and pests have widely been used in agricultural production. Consequently, an aerial pesticide application technology has become an effective way for plant protection in modern agriculture. The powerful technology is characterized to reduce the numbers and residues of pesticides for the better effectiveness of pesticide application. Alternatively, a high-voltage electrostatic device is often used to charge the spray droplets in an electrostatic spray system. Specifically, the chemical liquid is atomized into droplets near the nozzle to obtain a charge of the same polarity as the nozzle. An electrostatic field is then formed between the nozzle and the crop target under the action of high-voltage static electricity. As such, the droplets of opposite polarity are quickly adsorbed on the front and back of crop targets during the spraying process. Aerial electrostatic spraying is a deep integration of electrostatic spray system and aviation pesticide spraying in precision agriculture. The droplets can quickly be deposited along the power line in the process of aircraft spraying, thereby greatly reducing the drift loss for highly efficient deposition of droplets. Furthermore, the electrostatic spray technology has achieved excellent control effects on crops, fruit trees, and greenhouse vegetables in field tests. The top countries of aerial electrostatic spray technology in the world are the United States and Brazil, in terms of technology usage, and innovation. Particularly, the electrostatic spray technology in the United States has been fully commercialized for the aviation spraying equipment. In addition, an efficient aircraft is highly required for large-scale planting and plant protection in vast arable land and mostly plains in some developing countries. The manned fixed-wing aircraft is mainly used in electrostatic spray systems at present. This review outlined the international development of aerial electrostatic spraying technology to further clarify two main lines of reports at home and aboard, ranging from basic theoretical research to commercialization process. An application level of technology was set to analyze in China. The research on aviation electrostatic spray technology in China has presented a promising increase trend, due mainly to small environmental and topographical impacts in field tests. Moreover, the unmanned aerial vehicle (UAV) has become the most suitable aircraft equipped with an electrostatic spray system after long-term research. However, large research gaps still remained in manned vehicles and lately commercial plant protection UAV, compared with the state-of-the-art electrostatic spray technologies overseas. There were also numerously repeated and invalid studies overlapped in the main parameters in China. Anyway, it is still necessary to delve into the specific interaction mechanism between the process of spraying droplets and the operating parameters. The industrialized development of aviation electrostatic spray system was also reviewed at the end, together with the development prospects. Some suggestions were listed as: (1) The performance of each charge needed to be elucidated in the aerial electrostatic spray system. (2) The measurement technology of charged droplet deposition was highly demanding to accurately evaluate the actual properties of electrostatic spray. (3) Measurement of charge-to-mass ratio was necessary to rethinking using the cutting-edged quantum theories. An ever-increasing demand is coming soon using aviation electrostatic spray system for crop protection.