2012 Annual Report
1a.Objectives (from AD-416):
Objective 1: Investigate how droplet impact, retention, and evaporation are affected by target surface characteristics and pesticide formulation physical properties and establish a complex pesticide transfer function from fundamental research to new precision sprayer development.
Objective 2: Develop computer control systems for laser-guided precision sprayers to accommodate various tree canopy characteristics.
1b.Approach (from AD-416):
In cooperation with the ARS Application Technology Research Unit, Wooster, OH, perform the following: (1) determine evaporation time, spread factor and chemical residual pattern formation of droplets containing spray additives on horticultural leaves via sequential imaging under controlled conditions; (2) investigate influences of droplet size and velocity, spray formulation, and morphological surface of leaves on spray droplet impaction, retention and coverage to develop strategies for enhancing delivery to target areas; and (3) develop a precision air-assisted sprayer with multi-jet nozzles to reduce the amount of pesticides required by matching spray characteristics to specific types of nursery and fruit trees. A fast response, high resolution controller will be developed to control air velocity, spray application rate and number of jets required for each air jet nozzle. All these operations will occur as the sprayer moves past the tree, providing uniform spray coverage of the tree with minimum off-target loss beyond the tree row.
An electronic flow rate control system with microprocessors and pulse width modulation (PWM) controlled solenoid valves was designed to manipulate the output of spray nozzles independently to match tree structures which would be detected with a wide-range laser scanning sensor. The PWM signals to control nozzle flow rates were generated by the microprocessors based on laser sensor detections. Multi-channel driver and protection circuits for activating solenoid valves were developed to modulate variable-rate outputs in real time. An embedded computer (PC/104) along with a touch screen was used to process control algorithms and to fulfill communications between the operator and the control system. Laboratory tests demonstrated that the flow rate control system was able to achieve linear nozzle outputs with the duty cycle of PWM-controlled solenoid valves.
A variable-rate air-assisted sprayer implementing laser scanning technology was evaluated in an apple orchard by quantifying spray deposition at three different growing stages (April, May and June) with three sprayer treatments: the new variable-rate sprayer (S1), the same sprayer without the variable-rate function (S2) and a conventional air blast sprayer (S3). Their spray coverage and deposits inside canopies were measured and compared with water sensitive papers and nylon screens. The three sprayer treatments provided fairly consistent spray coverage and deposit in spray direction (or canopy depth direction) in the April test when tree foliages were in the early growth stages. The variations in spray coverage and deposit in spray direction increased considerably for S2 and S3 in the May and June tests. S1 produced better uniformity in spray deposit and coverage across tree height direction than S2 and S3 at all growth stages. Compared to conventional constant-rate sprayers, the new variable-rate sprayer only consumed 27% to 53% of the spray mixture while it still achieved adequate spray coverage inside canopies. Also, the spray deposition from the new sprayer was very consistent regardless of the canopy growth stages. The new sprayer was able to apply appropriate amount of pesticides based on tree canopy characteristics such as tree height, width, volume, foliage density and occurrence of trees, and thus increased spray efficiency and improved spray accuracy, resulting in reduced spray costs and potential environmental pollutions.
This research addressed critical elements for the development of precision sprayer technology envisioned in ARS parent project Objective 1 “Develop precision sprayers that can continuously match canopy characteristics to deliver agrichemicals and bio-products accurately to nursery and fruit crops”.