Evaluation of IrriGage collectors to measure irrigation depths from low pressure sprinklers

Coarse-grooved, fixed-plate sprinkler deflector pads provide distinct streams or jets of water that are not easily distorted by wind and minimize evaporative losses. However, these sprinklers provide variable, cyclic, and nonuniform application patterns of applied water that are difficult to accurately measure with collectors that have small openings. In 1999, 2000, and 2002, field studies were conducted to compare the measurement effectiveness of a non-evaporating sprinkler irrigation catch device (IrriGage) with larger collectors. The standard IrriGage has a 100-mm diameter opening, a 200-mm long collector barrel, and an attached storage bottle for collected water. These characteristics exceed current ASAE standard (ASAE S436.1) recommendations for sprinkler collectors. IrriGage collectors were compared to other catch devices that included 430-mm diameter pans (PAN) in 1999 and 2000, and a single row of 150-mm diameter collectors (150-S) similar to the IrriGage in 2002. IrriGage collectors were tested under three different sprinkler irrigation packages that included fixed-plate deflector pads with coarse grooves, spinning plates, and wobbling plates. In 1999, IrriGage collectors positioned with openings at a 1.2-m height within a corn canopy measured lower irrigation depths and different sprinkler patterns as compared to the larger diameter PAN collectors that were positioned in an adjacent grass buffer. In 2000, the 100-S collectors were lowered to a 600-mm height and repositioned into the grass buffer with the PAN collectors. The resultant measured irrigation depths and data variability for the IrriGage collectors were significantly greater and distributed differently than associated data from the PAN collectors. In 2002, a single row arrangement of IrriGage collectors (100-S) under the fixed plate sprinkler package had significantly greater irrigation depths (14% to 25%) and greater variances in collected data than the 150-S collectors (similar to 2000 results). However, while measured depths under spinning and wobbling plate sprinklers with 100-S collectors were 2% to 9% greater than measured depths with 150-S collector, differences were generally not significant. Furthermore, individual collector data between 100-S and 150-S collectors under the spinning and wobbling plate sprinklers tracked very well. Additional tests included multiple collector tests using inline (100-IL) and side-by-side (100-SS) arrangements of the 100-mm IrriGage collectors. Results from these tests showed that the 100-IL and 100-SS arrangements did not improve catch accuracy when compared to the individual 150-S collectors. The current ASAE standard (ASAE S436.1) for collector size criteria requires a minimum entrance diameter of just 60 mm. Based upon the field results of this work, the current standard collector size criteria are not appropriate for the low pressure, fixed plate, coarse-grooved sprinklers that provide distinct streams of water with little pattern breakup. Additional research is needed to determine an appropriate collector size (and perhaps shape) for the measurement of irrigation depths from center pivot and linear move irrigation machines with lower pressure sprinkler packages.