LAUSR

Variable rate irrigation (VRI) can increase water use efficiency and productivity by applying water based on site-specific needs. In this study, the performance of a five-span centre-pivot irrigation system (CPIS) retrofitted with a commercial variable-rate irrigation package was evaluated at constant and variable application depths at the Alberta Irrigation Technology Centre (AITC) in southern Alberta, Canada. Two sets of experiments were designed to investigate the uniformity of application of the system during the 2013 and 2014 growing seasons. The first set of catch-can trials were carried out with three irrigation rates in the direction of pivot travel. Three different wind regimes were observed during the catch-can trials. Catch-cans were arranged in grid configurations within the experimental plots located under one irrigation zone in span 4. The Christiansen coefficient of uniformity (CU) ranged from 90.4 to 94.4%. Wind speeds of 3.3 and 6.5 m s-1 negatively and significantly impacted the CU values. The second set of catch-can trials were performed with used and new sprinklers in a transect along the pivot lateral during the 2014 growing season. The Heermann and Hein coefficient of uniformity (CUHH) ranged from 89.0 to 93.5% and from 81.7 to 94.4% with constant and variable application depths, respectively. The greatest (94.4%) and least (81.7%) CUHH values were observed where water applications were 100 and 40% of the set point, respectively. Overall, the uniformity of application of CPIS retrofitted with the commercial VRI package both along the system's lateral and in the travel direction were above 90% for the majority of the trials under the different wind speeds and water application depths. Copyright © 2017 John Wiley & Sons, Ltd.