Effects of spray parameters on pesticide utilization efficiency and droplet deposition distribution in paddy field of self-propelled boom sprayer

A theoretical basis for the establishment of a high-efficiency pesticide application technology using self-propelled boom sprayer has been established. The diversities of pesticide utilization efficiency, deposition distribution uniformity, and droplet density on rice stem base during tillering stage, booting stage, and flowering stage were studied, respectively, when the self-propelled boom sprayer was applied with different spray pressure and spray volume. Ponceau G, a biological dye, was employed as the pesticide tracer to estimate the utilization ratio of pesticide under different spray parameters. The depositon uniformity was estimated with the value of coefficient of variation and absolute proportion. Water sensitive paper was used to collect the droplets on the rice stem base. And the data were used for analyzing the ability of pesticide droplets to permeate the rich canopy under different spray parameters. During the tillering stage, the average deposition rate of Ponceau G at each sampling site was only 0.11 mg under the spray pressure and spray volume of the self-propelled boom sprayer, which had been preset as 1.2 MPa and 375 L/hm², respectively. The result was 56.00% lower than that with the spray pressure and spray volume of 0.4 MPa and 300 L/hm². In terms of booting stage, the average deposition rate of Ponceau G at each sampling site is 0.26 mg under the spray pressure and spray volume of 1.2 MPa and 375 L/hm², which was significantly higher than those of the other four tested treatments. However, for the flowering stage, a smaller influence of the diversity of spray parameters on the deposition rate was observed. When appropriate spray pressure and spray volume were used, the maximum pesticide utilization efficiency achieved by the self-propelled boom sprayer during the tillering stage, booting stage, and flowering stage were 40.57%, 54.97% and 55.50%, respectively. Nonetheless, spray parameters had significant influence on the pesticide utilization efficiency during the tillering stage, which indicated the minimum utilization efficiency of 17.56%. Based on the coefficient of variation and absolute proportion, better pesticide distribution could be achieved when the spray pressure and spray volume of the self-propelled boom sprayer were preset to 0.8 MPa and 300 L/hm². The spray pressure had a significant influence on the droplet density on rice stem base. In the middle and late growth stages of rice, the droplet density on rice stem base was lower than 30 droplet/cm². The results demonstrated that the spray pressure and spray volume were two crucial influential factors for the pesticide utilization efficiency, spray deposition uniformity, and droplet density on rice stem base when self-propelled boom sprayer was used for rice-field operation. Overall, for the early growth stage, high-pressure, large-volume spraying was not appropriate. And in the middle and late growth stages, higher-pressured spraying may be necessary for a particular area to improve the control efficacy of plant diseases and insect pests of the rice stem base.