Forage And Grain Soybean Effects On Soil Water Content And Use Efficiency

Growing legumes in the southern Great Plains (SGP) during fallow periods between (Triticum aestivum L.) crops can protect soil, add N to soil, and supply high-quality summer forage. This study determined the water used, water use efficiency (WUE), and soil water depletion of forage (n=3) and grain (n=1) soybean [Glycine max (L.) Merr.] cultivars on silt loam soils following winter wheat harvest during the 2003 to 2005 summer growing season. Interactions (P < 0.001) in soil water content occurred between sampling date, cultivars, and years. More soil water was recorded under soybean in 2003 than 2004 or 2005, but was lower than in fallow plots. Year effects (P < 0.05) were recorded for standing crop, water used, and WUE. While cultivar effects were not significant P > 0.10). All cultivars used 2.0 to 2.5 times more water in 2004 and 2005 that 2003 (driest year). Forage production in 2003 (3034 kg ha(-1)) was 55% lower than in 2004 and 2005. Higher WUE (kg ha(-1) mm(-1)) was recorded in 2004 (16.0) than 2003 (13.2) or 2005 (10.9). Incorporating soybean into fallow periods following wheat generally limits the amount of soil water available for fall production of wheat forage in the SGP.