Date of this Version
Published in Precision Agriculture 14 (2013), pp. 307–322; doi: 10.1007/s11119-012-9296-z
The adoption of automatic section control (ASC) on agricultural sprayers remains popular since it reduces overlap and application in unwanted areas leading to input savings and improved environmental stewardship. Most spray controllers attempt to maintain the desired target rate during ASC actuation (ON and OFF of control sections which change the width of boom-section actually spraying) but limited knowledge exists regarding controller response and nozzle discharge variation during field operation. Therefore, field experiments were conducted using two common self-propelled sprayers equipped with commercially available control systems with ASC capabilities. Pressure transducers were mounted across the spray booms to record real-time nozzle pressure with data tagged with GPS location and time. Nozzle flow was obtained from nozzle pressure to compute nozzle flow uniformity or coefficient of variations (CVs) across the ON boom, off-rate errors (percent difference between actual and target nozzle flow rate) and settling times. Results indicated that nozzle CVs were >10 % for both auto-boom and auto-nozzle control systems, when each of the auto-boom and auto-nozzle sections were turned back ON for 0.5 and 0.2 s, respectively. Further, nozzle off-rate errors exceeding ±10 % occurred in both rectangular and irregular shaped fields. These off-rate errors primarily occurred during ASC actuation while at the same time the sprayer was being accelerated or decelerated. The extended nozzle flow settling times of up to 20 s (delayed response) indicated that the rate controller may require intelligent and enhanced control algorithms to minimize nozzle flow stabilization and thereby a reduction in sprayer off-rate errors during field operation.