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

Forages currently available to support yearling stocker cattle in the U.S. southern Great Plains (SGP) frequently have low quality during mid-July through September. This study tested the tropical/subtropical legume labial-, [LabLzbpurpureus (L.) Sweet] as both green manure and forage in central Oklahoma. We compared biomass production and nutritive value of lablab (cultivar Rio Verde) to soybean [Glycine max (L.) Merr.] grown during fallow periods of conventional and no-till wheat (Triticum aestivurn L. em. Thell) in 2008 to 2011. Biomass was collected at different growth stages during growing seasons and assayed for yield, N accumulation (kg N ha(-1)), crude protein (CP), and in vitro digestible dry matter (IVDDNI) concentration. Lablab produced more biomass than soybean (1415 vs. 1170 kg ha(-1) yr(-1), P = 0.02) across tillage systems; production declined over years < 0.01). Legume x year interaction (P <= 0.03) was noted in CP and IVDDNI. Lablab averaged (+/- 1 SD) more accumulated N than soybean 155(+/- 25) vs. 40(+/- 24) kg N ha(-1) yr(-1)] and had greater CP (P < 0.01) in all years; amounts in both species declined with length of study. Digestibility oflablab exceeded soybean (P < 0.01) throughout the study. We concluded that labial-, 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 double-cropping within wheat systems. Despite low production, lablab could be high quality forage for stocker cattle during late summer.