Scheduling Wheat Irrigations Using Infrared Thermometers and the Crop Water Stress Index in Arizona

Abstract

Durum wheat (Triticum turgidum L. var. durum ) is grown as a winter annual crop, normally in rotation with cotton, and in 1989, comprised 121,500 acres in Arizona. Winter rainfall is insignificant, therefore water is supplied totally through surface irrigation. The relationship between the timing and amount of irrigation water applied and grain yields have not been well -defined Field plot studies were conducted in 1986 and 1987 to test the feasibility of using the Crop Water Stress Index (CWSI) to time wheat irrigations and also to determine the relationship among the CWSI, grain production, and water applied The study was repeated at the commercial production level with a grower cooperator in 1989 to determine the usefulness of CWSI scheduling on large farms. Highest grain production was attained when irrigations were scheduled when the CWSI averaged 0.37 and 0.30 units on small plots for 1986 and 1987, respectively. At the grower production level, highest yields were attained when irrigations were scheduled when the CWSI averaged 0.17 units. In 1986 and 1987 scheduling irrigations at lower CWSI values did not significantly increase grain production while requiring more applied water than the optimum CWSI values. Scheduling irrigations at CWSI's exceeding the optimum values did significantly reduce grain production from the optimum, but required less applied water in all three years.