Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2001
Publication Date: 3/1/2001
Citation: Interpretive Summary: Irrigation scheduling guidelines are available for efficiently limiting the number of large surface irrigations applied to winter wheat during the spring. Similar information has not been available for the smaller, more-efficient irrigations scheduled with crop water use models and applied with center pivot irrigation systems. To develop this information, a two-year wheat irrigation study was conducted using wheat evapotranspiration data from the North Plains (of Texas) PET Network and highly efficient low energy precision (LEPA) and spray irrigation. Full irrigation to provide all water requirements of the wheat crop was compared with deficit spring irrigation treatments receiving 25, 50 or 75% of the full irrigation amount. Sprinkler irrigation was applied with the bubble and double ended sock LEPA methods and the above-canopy and overhead spray methods. Grain yields with 50% or more irrigation were in the 90 to 110 bu/ac range, and deficit irrigation with 25 or 50% of full spring irrigation utilized the pumped irrigation water most efficiently. The total available water supply, consisting of both irrigation and rainfall, was thus utilized efficiently over the entire 25 to 100% irrigation range. Irrigating winter wheat with fractions of PET is especially well suited to the low producing irrigation wells in the southern High Plains. Planting and emergence irrigating can be staggered over an interval of a month or more during the fall, and winter irrigation water requirements are low. During the spring when water use can exceed the capacity of wells, irrigation at only a fraction of the crop water requirement still results in highly efficient irrigation water use and effective use of rainfall.
Technical Abstract: A 2-yr deficit irrigation study was conducted to determine the water use efficiency of winter wheat (Triticum aestivum L.) irrigated with fractions of evapotranspiration during the spring irrigation season. Fully-irrigated treatment plots received sufficient irrigation to meet evapotranspiration as calculated by a Penman-Monteith grass reference evapotranspiration equation and locally derived crop coefficients. Deficit irrigation treatment plots received 0, 25, 50 or 75% of the fully irrigated amount on the same days. Irrigation was applied with a lateral move sprinkler system equipped with two LEPA methods, double-ended socks and bubblers, and two spray methods, above-canopy spray and overhead spray. All four sprinkler devices were spaced 1.52-m apart and located at the appropriate height for the sprinkler method. Cultural practices were similar to those used for high-yield wheat production in the southern Great Plains. Grain yields increased significantly with irrigation amount but not with sprinkler method. The full and 50% irrigation treatments averaged 7.0 and 6.32 Mg/ha for the two years. With 50% irrigation, seasonal water use efficiency averaged 0.95 kg/M3, and spring irrigation water use efficiency averaged 1.70 kg/M3, both being larger than all other irrigation amounts. The winter wheat, deficit-irrigated with fractions of spring ET, efficiently utilized seasonal water use consisting of irrigation, rainfall and stored soil water over the full 25 to 100% irrigation range. Spring irrigation was most efficiently applied at the 25 and 50% irrigation amounts. Deficit irrigation, as a fraction of spring ET, is well adapted to an irrigation water supply from low-producing wells, and provides efficient water use over a range of both rainfall and irrigation.