Orchard variable-rate spraying method integrating GNSS and wind-excited audio-conducted leaf area density

Hangxing Zhao^1*Shenghui YANG¹Wenwei Li¹Han Feng¹Shijie Jiang²Weihong Liu¹JIngbin Li³Yongjun Zheng¹Songchao Zhang⁴

• ¹China Agricultural University, Beijing, China
• ²Henan University of Science and Technology, Luoyang, China
• ³Shihezi University, Shihezi, China
• ⁴Key Laboratory of Modern Agricultural Equipment, Ministry of Agriculture and Rural Affairs, Naijing, China

Conventional air-assisted sprayers for orchard are characterized by three major limitations: excessive pesticide wastage, high residual pesticide levels and uneven pesticide distribution on fruit trees. To address these challenges, precision spraying technologies have been developed, enabling dynamic adjustment of spraying parameters based on canopy characteristics. Leaf area density is one of the most effective indicators for characterizing canopy sparseness. However, accurately and automatically measuring canopy leaf area density remains difficult due to the shading effects of leaves. Consequently, few studies have developed fully operational variable-rate spraying systems based on canopy leaf area density. This paper proposes a variable-rate spraying method integrating global navigation satellite system (GNSS) and wind-excited audio-conducted leaf area density. Firstly, a small self-propelled variable-rate spraying platform for orchards was designed, capable of acquiring orchard-wide positioning data via GNSS and obtaining canopy leaf area density information through wind-excited audios. Then, a prescription map generation method integrating orchard-wide positioning information and canopy leaf area density was developed. Thirdly, a variable-rate spraying control model and algorithm utilizing orchard-wide leaf area density distribution were created, leading to the integration of the complete variable-rate spraying system based on orchard-wide distribution of leaf area density. Finally, field tests were conducted in orchards to evaluate spray control accuracy and droplet deposition performance, demonstrated that the system achieved an average relative error of only 5.52% in spray flow rate regulation. Compared with the constant-rate spraying, the variable-rate spraying mode reduced the longitudinal coefficients of variation (CV) of canopy droplet deposition by 55.75% on the adaxial leaf surface and by 33.22% on the abaxial leaf surface, while the maximum reduction in transverse CV reached 62.32%. Furthermore, the ground runoff of spray solution decreased by 62.29%, and the droplet deposition density on leaf surfaces exceeded 25 droplets per cm², meeting the low-volume application standard for insecticide products. This study is expected to provide a technical solution for the development of precision plant protection equipment in orchards.