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FORAGE & GRAZINGLANDS

Water Use by Five Warm-Season Legumes in the Southern Great Plains

USDA-ARS, Grazinglands Research Lab., 7207 W. Cheyenne St., El Reno, OK 73036

^* Corresponding author (srinivas.rao{at}ars.usda.gov).

Growing warm-season legumes during fallow periods associated with traditional continuous systems of winter wheat (Triticum aestivum L.) in the southern Great Plains (SGP) can provide supplemental forage, biological N, and protection from soil erosion, provided the legumes can tolerate drought stress and not deplete the available water in the soil profile. Our objective was to quantify water use by five species of pulse legumes {pigeon pea [(Cajanus Cajan (L.) Millsp.) cv. GA-2], guar [Cyamopsis tetragonobloba (L.) Taub., cv. Kinman], cowpea [Vigna unguiculata (L.) Walp., cv. Chinese red], mung bean [Vigna radiate (L.) Wilcz., cv. Berkins], and soybean [Glycine max (L.) Merr., cv. Hutcheson (the control)]}. Seeds were inoculated and planted after wheat harvest in mid-June 2003 through 2006. The amount of water in the upper 65 cm of the soil profile was measured on nine dates [from 45 d before planting legumes to 195 d since planting (DSP)]. Significant (P < 0.01) differences in soil water were recorded among treatments, dates, and years. Differences in soil water among fallow, cowpea, and mung bean were less following the 2003 and 2004 summer seasons and most noticeable in 2005 and 2006. Mung bean, guar, soybean, and pigeon pea used the greatest amounts of water in 2005, the wettest season, while cowpea and mung bean used the least in 2003. Mung bean, cowpea, and guar generated smaller water deficits and used less soil water, in three of four years, and could be effective in wheat-summer legume rotations in the SGP.

Abbreviations: DSP, date since planting • FWUE, field water use efficiency • MG, maturity groups • NWUE, nitrogen water use efficiency • SGP • southern Great Plains