Green Manure and Forage Potential of Lablab in the Southern Plains.

Current summer forages available to support grazing by yearling cattle in the U.S. southern Great Plains have a mid-July through September quality gap.  This study tested the function of the tropical/subtropical legume lablab [Lablab purpureus (L.) Sweet] as green manure or forage in central Oklahoma. We compared biomass production and nutritive values of lablab and soybean [Glycine max (L. (Merr.)] grown during fallow periods, of continuous systems of wheat (Triticum aestivum L. em.Thell) during 2008 through 2011, under conventional or no-till management.  Biomass produced by legumes was collected during growing seasons and assayed for yield, nitrogen accumulation (kg N ha^-1), crude protein (CP) and in vitro digestible dry matter (IVDDM) concentrations. Lablab produced more biomass than soybean (1415 vs. 1170 kg ha^-1; P=0.02) across tillage systems. Production by both legumes declined over years (P<0.01).  Legume x year interactions (P≤0.03) was noted in CP and IVDDM concentrations. Lablab accumulated more N than soybean (95 vs 72 kg N ha^-1) and had greater CP concentrations (P<0.01) in all years; amounts in both species declined in later years. Digestibility of lablab exceeded soybean (P<0.01) throughout the study. We concluded lablab contributed more biomass and N than soybean as green manure or forage within continuous systems of wheat production. Function of both legumes was limited by low precipitation and continuous application of summer crops within wheat systems. Though production was low, lablab could provide stocker cattle with more forage than soybean during late summer. Future studies should test lablab under grazing by stocker cattle.