Water Use by Grazed and Ungrazed Pigeon Pea is Similar

Water use by the warm-season annual pulse pigeon pea [Cajanus cajan (L.) Millsp] must be described for this legume to be effectively used as grazed summer forage in the southern Great Plains (SGP). A study was conducted in central Oklahoma during 2008 to 2010 to quantify soil water content, water use, and water-use efficiency (WUE) in six grazed 0.41 ha paddocks planted to two short-duration cultivars (GA-2, MN-8). Exclosures (9 m(-2)) were established to measure biomass, and crossbred stocker cattle (n = 3) grazed the paddocks during August through October. Total water content in the upper 57.5 cm of soil was quantified by neutron density gauge at planting, flowering, and end of growing season (EOS), to calculate water use and WUE in producing aboveground biomass. Grazing main and interaction effects were not significant on available soil water (0.13 < p < 0.50), or water use (0.10 < p < 0.62). Cultivar x year x time of season interactions on water use were significant (p <= 0.02), due to 49% greater water use by MN-8 in 2008 (wettest year). Lowest water use within years occurred at flowering and the lowest overall occurred in 2009 (driest year). Year and time of season main effects on WUE were significant (p < 0.01); WUE in 2009 and 2010 (8.1 and 9.4 kg mm(-1), respectively) differed from 2008 (4.7 kg mm(-1)), and was lower at flowering than EOS (5.9 vs. 9.1 kg mm(-1)). Results showed conditions during growing seasons had greater effects on water use by short-duration pigeon pea than grazing or cultivar planted.