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Title: Green manure and forage potential of lablab in the U.S. southern plains

item Northup, Brian
item Rao, Srinivas

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2014
Publication Date: 5/5/2015
Citation: Northup, B.K., Rao, S.C. 2015. Green manure and forage potential of lablab in the U.S. southern plains. Agronomy Journal. 107(3):1113-1118.

Interpretive Summary: Grazing programs in the southern Great Plains (SGP) that have developed since the 1950’s have sought to support yearling stocker cattle with high-quality forage for long periods. One time of the year that has always presented challenges to stocker producers is late-summer. However, the combination of low soil moisture, changing environmental conditions, and short growth cycles of the primary forages of the region are challenges to meeting this goal. As such, there is no single forage capable of meeting this goal, which has led to the trialing of many warm-season annual forages during the summer fallow of winter wheat pasture. Double cropping winter cereals with summer legumes is an important farming practice in many regions of the USA. However, it is not common in the southern Great Plains (SGP), because of low amounts, and unpredictable timing, of rainfall. In this study we tested how a Texas-developed cultivar of the tropical legume lablab (cv. Rio Verde) functioned as a green manure or forage within continuous systems of wheat production in central Oklahoma, during 4 drought-affected years, and compared results to soybean. The amounts of forage produced by both legumes declined during the later years of the study due to shortages of moisture, and continued double-cropping with winter wheat. However, we found that lablab still produced 21% more forage than soybean. Lablab forage had crude protein contents that averaged 24%, compared to 17% for soybean, and digestibility of 85% compared to 74% for soybean. Despite the effects of dry growing conditions, we found that lablab was more effective as a late-summer forage or green manure. Future studies should test lablab as late-summer grazed forage in central Oklahoma in a single crop setting.

Technical Abstract: Current perennial summer forages available to support grazing by yearling cattle in the U.S. southern Great Plains have mid-July through September quality gaps. 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 (cv. Rio Verde) to soybean [Glycine max (L. (Merr.)] grown during fallow periods of continuous wheat (Triticum aestivum L. em.Thell) systems (conventional and no-till) during 2008-2011. Biomass produced by legumes was collected during growing seasons and assayed for yield, nitrogen accumulation (kg N/ha), crude protein (CP) and in vitro digestible dry matter (IVDDM) concentrations. Lablab produced more biomass than soybean (1415 vs. 1170 kg/h/y, 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 averaged (± 1 s.d.) more accumulated N than soybean [55(±25) vs. 40(±24) kg N/ha/y] and had greater CP concentrations (P<0.01) in all years; amounts in both species declined with length of study. Digestibility of lablab exceeded soybean (P<0.01) throughout the study. We concluded that 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. Despite low production, lablab could be effective forage for stocker cattle during late summer. Future studies should test lablab under grazing by stocker cattle in mono-crop settings.