Understanding the causes of variable ET in a field is critical for maximizing yield on a per-acre basis as well as for proper irrigation scheduling and regional water management. Since 2004, the ITRC has provided technical irrigation support and management for over 2,000 acres of center pivot irrigated forage crops being supplied by reclaimed water near Palmdale, California. Irrigation scheduling is conducted using a daily soil water balance dual crop coefficient approach. Detailed records on planting and harvest dates, daily water applications, pivot run speeds, and annual distribution uniformity evaluations are maintained along with daily reference evapotranspiration data from a station on site. Since accurate records on pivot distribution uniformity are available, and most of the pivots were under moderate deficit irrigation in one of the years analyzed, a portion of the spatial variability in ETc can be attributed (quantifiably) to this non-uniformity in irrigation distribution. During 2010, the same fields were fully irrigated (no water stress) during the evaluation period because a reservoir was constructed on site. The variability in ETc during the non-water stressed conditions can be attributed to causes other than irrigation DU. Comparing the uniformity of evapotranspiration from the same fields, with the same crops, under both water stressed conditions, the uniformity of evapotranspiration due to irrigation system DU (ET_UDU) was quantified. The results indicate that under moderate water stressed conditions, the ET_UDU contributes approximately 55% to the overall non-uniformity of evapotranspiration in a field.


Bioresource and Agricultural Engineering

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URL: https://digitalcommons.calpoly.edu/bae_fac/256