Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2001
Publication Date: N/A
Citation: Interpretive Summary: Dairy farmers and other livestock farmers need more sustainable ways to produce meat and milk. The introduction of forage legumes in pastures helps improve forage quality and animal production, provides more equal forage yield over the growing season, and reduces the need for commercial nitrogen fertilizer. This latter characteristic is due to the unique ability of legumes to obtain nitrogen from the air by a symbiosis with bacteria known as rhizobia. Forage legumes currently used in pastures, like red and white clover and birdsfoot trefoil, are known to fix large amounts of nitrogen, but they often do not persist in northern climates over the long term. Kura clover is a relatively new forage legume species to the USA. It is very persistent and could help alleviate problems associated with other forage legume species. The use of Kura clover in the USA is currently limited because of difficulties in establishing the seedlings. We discovered that root nodules are very slow to establish on Kura clover roots, so nitrogen fixation from the atmosphere was very limited during the stand establishment year. By applying both rhizobia and fertilizer nitrogen to new Kura clover seedings, first-year forage yields were more than doubled and the crop continued to grow better the next year. This simple technique will help farmers establish this valuable new forage legume on their farms, which will eventually reduce the need for purchased nitrogen fertilizer and improve the sustainability and profitability of producing livestock products.
Technical Abstract: Kura clover (Trifolium ambiguum M.B.) is a persistent rhizomatous forage legume whose use is currently limited by a slow establishment. In three environments, we determined the effects of rhizobial inoculation and N fertilization on Kura clover growth and N2 fixation in the seeding year. Kura clover was seeded with or without a commercial rhizobial inoculant and dwith and without N fertilization. Fertilization treatments consisted of 10 kg N ha-1 either applied at seeding or split in 10 kg N ha-1 applications every other week after seeding. Kura clover seeding year response to rhizobial inoculation was low across environments, while response to N fertilization was consistently positive. Averaged over environments, split application of N increased maximum herbage yield 125% compared to non- fertilized plots; in contrast, rhizobial inoculation increased yields by only 50%. Root and rhizome mass responses to N fertilization and inoculation were similar to that of herbage. Herbage yields varied with environment but were as high as 5.5 Mg ha-1 with split-application of N. Limited response to rhizobial inoculation was associated with slow nodulation, the first nodules being observed 50 DAS (days after seeding). As a consequence, N2 fixation in the seeding year averaged only 17 kg N fixed ha-1 with only 24 %Ndfa (percent N derived from the atmosphere) across all environments. However, Kura clover responded to inoculation in the post-seeding year while maintaining its response to N fertilization. Kura clover establishment was N-limited when inoculated with currently available commercial rhizobial inoculants and N fertilization benefitted Kura clover establishment.