FIELD SCALE LIMITED IRRIGATION SCENARIOS FOR WATER POLICY STRATEGIES

Abstract

Approaches to reducing irrigation inputs to crops have been studied for the past 50 to 60 years in research settings.Fewer efforts have been made to document limited irrigation responses over a number of seasons on commercial fields. Thisstudy compared farm-based irrigation management (FARM) with best management practices (BMP), late initiation ofirrigation (LATE), and a restricted allocation (ALLOC). These irrigation management strategies each occupied 1/8 of acenter pivot system in southwest Nebraska in continuous corn production, on four cooperating farms, which were replicatedat the same sites for 3 to 6 years. Irrigation variables were achieved by irrigating or not irrigating, or by speeding up orslowing down the center pivot. When the grain yields and irrigation amounts were normalized each year using the FARMtreatment as the basis, on average for three of four locations, the BMP treatment yielded equal to the FARM treatment, theLATE treatment yielded 93% of the FARM treatment and the ALLOC yielded 84% of the FARM treatment. At the same time,it took 76% and 57% of the water for the LATE and ALLOC treatments, respectively, to achieve these yields. The adjustedgross returns (yield . price irrigation treatment costs) of the irrigation treatments were analyzed for each location. Whenthe gross returns were normalized using the FARM treatment as the basis, FARM and BMP returns were equal acrosscombinations of high and low input commodity prices and pumping costs. The LATE treatment gross return was 95% of FARMreturn. The gross return for the ALLOC treatment was 85% to 91% of the FARM treatment. The higher the water costs, thelower the difference between the highest and lowest returning water treatments. Relationships between evapotranspirationand grain yield were developed for two sites over the limited range of water applications of the projects. Regressions indicatedmore variability between the commercial field data and research plot environments. Much of this difference may have beendue to yearly replication in this study rather than plot-to-plot replication in the research center study. Yield and irrigationdata were normalized on the basis of the FARM treatment. Normalized yield irrigation results over years and locations forthree of the four locations showed declining yields as irrigation decreased. The same regression was used to normalize thelocations with soil textures from fine sand to sandy loam, which suggested that the three locations behaved similarly withrespect to the management treatments.