Submitted to: Journal of Sustainable Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2009
Publication Date: January 25, 2010
Citation: Bartholomew, P.W., Williams, R.D. 2010. Overseeding unimproved warm-season pasture with cool- and warm-season legumes to enhance forage productivity. Journal of Sustainable Agriculture. 34:125-140. Interpretive Summary: Farmers throughout the southern plains are commonly faced with a problem of feed shortage for livestock between late fall and early spring, when it is too cool for warm-season pastures to grow. Forage legumes have the potential to increase forage production early and late in the year, because they can grow at lower temperatures than the summer grasses. For low-input farming systems forage legumes may be particularly useful because not only can they provide feed of high quality, but they may also contribute to improvement of soil fertility. If the types of legume grown are persistent from year to year, or are able to re-establish by self-seeding, this will also allow costs of regular reseeding to be avoided. An experiment was carried out to test different cool- and warm-season legumes overseeded into unimproved summer pasture. Cool-season legumes were crownvetch, hairy vetch, black medic or white clover and these were sown either alone or in combination with Korean lespedeza as a summer legume. To reinforce the initial sowing, seeds were resown in the second year of the experiment. In the two growing seasons immediately following sowing, hairy vetch and black medic were productive, but they did not reseed well and production in the final two years of the experiment was low. Crownvetch and white clover were slow to establish and produced little forage in the first two years of the experiment, but increased production in the final two years. On average over four years, when lespedeza was included in a mixed pasture, production was increased by 15%, or about 410 kg/ha/yr. Increased legume production decreased summer grass production, but the net gain in overall pasture production was about 0.75 kg for each 1 kg of legume produced. The experiment demonstrated that perennial legumes such as crownvetch or white clover may require several years before becoming established and productive in an existing pasture. Annual cool-season legumes such as hairy vetch and black medic cannot be relied upon to re-establish by self-seeding, but are likely to increase the productivity of pasture if resown each year. Lespedeza appears to self-seed better than hairy vetch and black medic and can also increase pasture productivity.
Technical Abstract: Cool-season forage deficit in the southern Great Plains of the U.S.A. leads farmers to provide purchased feed for livestock over prolonged periods, with negative impact on enterprise profitability. Forage shortage might be mitigated by overseeding forage legumes into existing warm-season pasture. Unimproved warm-season grass pastures were overseeded with Korean lespedeza (Lespedeza stipulacea Maxim) or were not overseeded with summer legume. These same plots were subsequently overseeded with hairy vetch (Vicia villosa Roth), crownvetch (Coronilla varia L.), black medic (Medicago lupulina L.) or ladino white clover (Trifolium repens L.) or, not overseeded with cool-season legume. Including lespedeza in a forage mixture increased total forage yield by an average of 15%, or 1640 kg ha-1 over 4 years. Overseeding with cool-season legumes provided a net benefit in total forage yield of 0.75 kg for each 1.0 kg of legume produced. Yield increases resulting from overseeding with hairy vetch or black medic were largely limited to the harvest season following sowing, but overseeded crownvetch or white clover provided limited short- to medium-term yield benefit. Regeneration of hairy vetch, black medic or lespedeza by self-seeding presents problems of harvest timing that may be difficult to resolve in mixtures of warm and cool-season crops. Annual overseeding may be a more reliable method of ensuring that legumes make a practically significant contribution to total forage production in mixtures with warm-season grasses.