|Zhu, Yan Ping - UNIVERSITY OF MINNESOTA|
|Sheaffer, Craig - UNIVERSITY OF MINNESOTA|
|Graham, Peter - UNIVERSITY OF MINNESOTA|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 1999
Publication Date: N/A
Interpretive Summary: Annual Medicago species (medics) are fast growing legumes that can fix nitrogen in symbiosis with the soil bacterium Sinorhizobium. They may be useful in suppressing the growth of weeds and in providing nitrogen to accompanying crops or crops grown in rotations. Annual medics have been introduced into the Upper Midwest for use in crop management schemes aimed at sustainable agriculture. However, little information is available on th prevalence of Sinorhizobium strains in soil and which strain in commercial inoculants are best suited for use in Minnesota. The objectives of experiments reported in this study were to assess the efficacy of commercial medic inoculum on inducing nitrogen fixing root nodules with several annual medic species and to determine whether inoculation of soil was needed for the growth of annual medics. All annual medic species, except Medicago rugosa, nodulated well without application of commercial inoculum. Inoculation of Medicago rugosa improved the number of plants nodulated and plant growth. Within the annual medic commercial inoculum strain number 102G3 was most prevalent in nodules. In Minnesota soils Sinorhizobium meliloti that can nodulate annual medics is quite prevalent. These studies are important because they show that use of most annual medics in Minnesota is feasible without the need for inoculation. However, if Medicago rugosa is used, the farmer needs to buy commercial inoculum and apply it to fields. Moreover, successful commercial inoculum should contain high quantities of Sinorhizobium strain number 102G3.
Technical Abstract: The N2 fixation potential of annual medics in the Upper Midwest USA has been evaluated. However, the effectiveness and competitiveness of inoculant strains and possible preference for individual strains by different annual medics are unknown. Moreover, information on the effects of inorganic N on nodulation and growth of annual medics is lacking. Our objectives were to determine the effect of N fertilizer and commercial medic inoculum on nodulation, dry matter, and N yield of annual medics; dinitrogen fixation by medics; and Sinorhizobium strain occupancy in nodules of annual medics. Experiments were conducted on a sandy, mixed Udorthentic Haploboroll at Becker, MN. The experimental design was a randomized complete block with treatments in a split-plot arrangement. Whole plot treatments were factorial combinations of inoculation (+I or -I) and fertilizer N (+N or - N). Subplot treatments were seven annual and one perennial Medicago spp. Nodule strain occupancy was subsequently evaluated for four annual medic species grown at Becker and St. Paul (a fine-loamy, mixed, Typic Hapludalf) using antisera prepared against six Sinorhizobium strains and the indirect Enzyme-linked Immunosorbent Assay (ELISA) procedure. Annual medics except M. rugosa nodulated well without application of commercial inoculum. Inoculation improved the percent of plants nodulated (PPN) and nodule mass score (NMS) of M. rugosa with no N fertilizer application. Nitrogen fertilizer reduced nodulation of all medics by reducing PPN or NMS. Commercial inoculum and N fertilizer effects on herbage DM and N yields varied with seeding date and legume species. Among the five strains in the commercial inoculum for annual medics, 102G3 was the most prevalent in nodules and 102H2 the least prevalent.