Catch-can performance under a line-source sprinkler

A line-source sprinkler configuration provides a linearly decreasing irrigation application rate perpendicular to the sprinkler line and has been utilized to study crop response to variable irrigation amounts. The effect on measured irrigation application depths from using various types of catch-cans in those studies is not known. Derived relationships between crop yield and applied water is dependent on the accuracy of measured catch-can water volumes. The purpose of this study was to evaluate catch-can characteristic effects on measurement of sprinkler irrigation depths in a line source. This was accomplished by evaluating six types of catch-cans: (1) 83 mm diameter polypropylene separatory funnel (with evaporation-suppressing oil), (2) 82 mm diameter PVC reducer can (with evaporation-suppressing oil), (3) 151 mm diameter metal can, (4) 64 X 59 mm wedge rain gauge, (5) 146 nun white plastic bucket, and (6) 100 nun diameter clear plastic funnel rain gauge. The cans were placed at five application rate conditions (2.8, 5.5, 8.7, 12.6, and 14.8 mm/h). Cumulative catch depths differed among the catch-can types. However, only the metal can and white bucket cumulative application depths at the lowest application rate were statistically different from those of the control (separatory funnel). Catch-cans with a larger diameter opening exhibited less variation in catch depths. Measured evaporation of standing water from catch-cans varied from 0.04 mm/h (funnel rain gauge) to 1.81 mm/h (separatory funnel without evaporation-suppressing oil). Water applied to a bucket's sidewall evaporated at a higher rate than standing water. Inaccuracy of application depth measurement may occur at low application rates even when catch-cans meet the ASAE Standard. The relatively good performance of the funnel rain gauge and catch-cans with evaporation-suppressing oil (and subsequently less depth than the ASAE Standard requires) suggests that it may be appropriate to re-evaluate the standard to consider such devices.