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Intelligent Sprayer Spray Rates Optimization to Efficiently Apply Chemicals in Modern Apple Orchards

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Journal of the ASABE. 65(6): 1411-1420. (doi: 10.13031/ja.14654) @2022
Authors:   Anura P Rathnayake, Ramesh K Sahni, Lav R Khot, Gwen A Hoheisel, Heping Zhu
Keywords:   Intelligent sprayer, Modern orchard systems, Spray rate, Tree row volume, Unit canopy row.

Highlights

Intelligent sprayers require crop canopy-specific base spray rate (SR) adjustments.

SRs can be estimated by Tree Row Volume (TRV) and Unit Canopy Row (UCR) methods.

This study formulated TRV and UCR based SRs for modern apple orchard canopies.

Field trials evaluated spray deposition and coverage variations for these rates.

TRV and UCR based treatments had comparable spray performance to the grower-adapted application rate.

Abstract. The efficiency of air-assisted sprayer-based chemical applications in horticultural crops is dependent on several factors, including that of the application rate as the amount of liquid per ground area (L ha-1 or gal acre-1 [GPA]). In contrast to the conventional GPA-based application rates, recently developed intelligent and precision sprayers use the input spray rate (SR) as the amount of liquid volume (L) required to spray one cubic meter of crop canopy (L m-3 or ounces per cubic foot). This input rate ranges between 0.06 and 0.13 L m-3 depending on the architecture and canopy size. However, the exact value of input SR is decided based on grower experience and manufacturer recommendation and can often be a broad estimation. Therefore, this study was conducted to explore methods that could be used to have a precise estimate of the input SR related to the canopy being sprayed for optimal spray applications. Tree row volume (TRV) and unit canopy row (UCR) methods were used to estimate input SRs and the sprayer field efficiency was evaluated in a vertical fruiting wall-trained commercial apple orchard, typical in the State of Washington, USA. Field spray trials were conducted in the full canopy growth stage, spraying a mix of fluorescent tracer dye of 2 g L-1 concentration at a calibration speed of 1.50 m s-1. Spray deposition and coverage were evaluated in replicated field trials using deposit samplers (mylar cards and screen) and water-sensitive papers, respectively. Test results demonstrated that both TRV (SR: 0.09 L m-3) and UCR (SR: 0.10 L m-3) were effective methods to calculate the spray rates since their spray deposition and coverage were comparable to that of the grower-adapted application rate (935 L ha-1). While the spray rates calculated by both methods provided better application efficiency, an SR of 0.09 L m-3 calculated by the TRV method would be preferable in spray applications of fully foliated fruiting wall-trained apple trees as it sprayed less liquid. Although the TRV method could potentially be applicable for estimating SR with an adjustment factor to compensate for the pruning level, crop-specific further evaluations are suggested for different canopy training systems.

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