Introduction
Irrigation scheduling methods in the irrigated far west are not uniformly accepted and depend on irrigation system, production economics and the management investment the grower is committed to. Most current and successful methods use soil and/or plant-based measurements that are combined with regional estimates of ETa and Kc to calculate best irrigation timing. Growers that make use of the available technology find that the time and financial costs invested in making careful field evaluations improve farm economics. Seasonal cotton water use for optimum yields can exceed 750 mm (30 inches) with typical rainfall contributions less than 15 percent of total season water requirements. Crop water requirements are distributed unevenly across the season with very low ET observed in the 60 days following planting and peak ET observed 100 to 115 days after planting. The highest cotton water use period is from late June to mid August during peak-bloom with daily water use of slightly over 2.0 inches per…