EVAPOTRANSPIRATION, YIELD, AND WATER-USE EFFICIENCY OF CORN HYBRIDS DIFFERING IN MATURITY

Short-season corn (Zea mays L.) hybrids may reduce irrigation requirem ents and permit earlier harvest. We measured and compared evapotranspi ration (ET) of a short-season (SS, Pioneer 3737) and full-season (FS, Pioneer 3245) hybrid under full irrigation in 1994 at Bushland, TX, an d examined differences in growth, yield, and water use efficiency (WUE ). Both hybrids were planted the same day in contiguous 4-ha fields (e ach field with a weighing lysimeter to measure ET directly), were irri gated simultaneously until the SS hybrid reached mid grain fill (R5 de nt stage), and were managed for high productivity. Harvest was at the normal field-dried grain water content of 136 g kg(-1) for the region, Rainfall was 320 mm; 465 and 577 mm of irrigation was applied to the SS and FS hybrid fields, respectively. Seasonal ET was reduced with th e SS hybrid (SS, 673 mm; FS, 802 mm), with the primary reduction after SS anthesis. Peak daily ET rates (some >10 mm d(-1)) were not affecte d by hybrid type. Grain yields (dry basis) declined from 1322 to 1130 g m(-2), but grain water use efficiency (WUEg = grain yield/ET) was si milar across hybrids: SS, 1.68 kg m(-3); FS, 1.65 kg m(-3). Dry matter (DM) was reduced by >390 g m(-2) for the SS hybrid, but DM water use efficiency (WUEd = DM/ET) was identical for the two hybrids, at 3.02 k g m(-3). The SS hybrid reached physiological maturity 12 d earlier tha n the FS hybrid and was harvested 11 d sooner. Leaf area index was >5. 5 m(2) m(-2) for the FS hybrid, but barely >4 m(2) m(-2) for the SS hy brid. The WUEd, WUEg, and peak daily ET rates were not appreciably dif ferent for the two hybrids when fully irrigated, although seasonal ET was less with the SS hybrid. A shorter-maturity hybrid can reduce ET a nd seasonal irrigation requirement, but it will not reduce the needed irrigation capacity (now per unit area) by more than 5 to 10%, as that is largely dictated by the near-maximum daily ET rate needed to avoid soil water deficits and a corresponding yield reduction. With prevail ing regional pumping and production costs, the reduced production inco me with a SS hybrid would be more than six to eight times the saving i n irrigation water cost, but this could be offset by higher grain mark eting prices with an earlier harvest and by the opportunity for grazin g income from a winter wheat (Triticum aestivum L.) double-crop.