INOCULATION OF ALFALFA SEED FOR INCREASED YIELD ON MODERATELY ACID SOIL

Abstract

Methods currently available for inoculating alfalfa (Medicago sativa L.) seed with Rizobium meliloti were evaluated to determine their ability to produce effective nodulation and to increase forage yield under moderately acid (pH 5.8–5.9) soil conditions. Five inoculation treatments were applied in a field experiment: no inoculant, 5.5 g inoculant/kg seed applied without inoculant sticker, 5.5 g inoculant/kg seed applied with inoculant sitcker, 50.7 g inoculant/kg seed applied with inoculant sticker, and 5.4 g inoculant/kg seed applied with a commerical seed-coating process. Alfalfa yields were not increased relative to the uninoculated control when inoculant was applied without sticker at 5.5 g inoculant/kg seed. However, when the inoculant was applied at 50.7 g/kg seed using a sticking agent alfalfa yields were increased 85% during the first harvest year and 47% in the second harvest year. Lower, but significant yield increases were obtained with 5.5 g inoculant/kg seed applied with a sticking agent and 5.4 g inoculant/kg seed applied with the commerical seed-coating process. In an assay conducted in the greenhouse, double antibiotic (streptomycin, rifampicin) resistant strains of R. meliloti were used to determine the proportion of nodules formed by the inoculant Rhizobium. Between 92 and 100% of the nodules contained antibiotic resistant strains when the inoculant was applied with a sticking agent or with the seed-coating process, while only 38% of the nodules in the treatment without sticker contained antibiotic resistant strains. The results demonstrate the importance of applying inoculants with a sticking agent or in conjunction with seed coating to obtain maximum yields of alfalfa on moderately acid soils. Key words: Acid soil, Rhizobium meliloti, Medicago sativa, inoculation, antibiotic resistant mutants