Field Evaluation of Selected Rhizobium in an Improved Legume Inoculant¹

Abstract

Increased grain legume production depends on effective symbiotic dinitrogen fixation through successful legume inoculation. Inoculants containing high numbers ≥ l07/g of effective Rhizobium must withstand adverse field conditions. Field studies were performed to determine the effects of selected rhizobia in two different inoculant carriers on nodulation and performance of three grain legumes. The soil at the 1979 site (Vertic Haplaquept) contained = 103 cowpea Rhizobium and = 102 Rhizobium phaseoli per g of dry soil. The soil at the 1980 site (Typic Paleudalf) contained < l02 R. phaseoli per g of dry soil. Selected strains of R. phaseoli and cowpea Rhizobium were incorporated in peat or vegetable oil. Seeds of bean (Phaseolus vulgaris L.), cowpea [Vigna unguiculata (L.) Walp.], and peanut (Arachis hypogaea L.) were inoculated (ca. 108 Rhizobium/seed) and planted. Nodulation, plant growth, and yields were determined in all experiments. Strains of Rhizobium in oil‐base inoculants generally formed a greater percentage of nodules on plants than did the same strains applied in peat‐base inoculants. Rhizobium phaseoli 971A occupied 93% of bean nodules when applied as oil‐base inoculant but only 82% when applied as peat‐base inoculant. Fresh weight bean yields of 5,620 kg/ha were obtained with strain 971A (oil‐base) compared to 3,370 kg/ha for the peat‐base treatment. Similar significant yield increases were obtained for cowpeas and peanuts inoculated with oil‐base inoculants. These experiments indicate that an improved inoculant provided high numbers of effective Rhizobium at planting. Through subsequent effective nodulation, oil‐base inoculants increased yields and nitrogen fixation by the legumes due to increased nodulation by the superior N2‐fixing strains of Rhizobium.

Development of environmental friendly bioinoculate for peanut (Arachis hypogea L.) production in Eastern Ethiopia

“…This result clearly indicated that the native rhizobia effective in supplying N to host plants as the inoculated isolates did. In line with this result, Kremer and Peterson (1983) found that the N 2 fixation by peanut has been only increased when the inoculation improved the nodule weight.…”

Analysis of host genotype x rhizobial strain interaction in N2 fixation

“…However, correlations between the two groups were not high. Similar results were reported in cowpea (MILLER et al, 1986) and other legumes (KREMER & PETERSON, 1983;HEICHEL et al, 1981).…”

Soil Biology of the Rhizobiaceae

“…As a result, inoculant rhizobia may only form 5-10% of the nodules produced in the first year, with the frequency with which they are found in nodules declining even further in subsequent crops. This has usually been perceived as a problem of competition between the inoculant rhizobia and those that are indigenous to the soil and has led to an intensive research effort emphasizing: (1) the selection of strains for competitive ability (Berg et ai., 1988;Caldwell, 1969;Johnson and Means, 1964;Klubek et al, 1988;Smith and Wollum, 1989), (2) the use oflarger than normal inoculation rates (Kapusta and Rouwenhoest, 1973;Weaver and Frederick, 1974a;, (3) development of improved inoculant carriers and delivery systems (Boonkerd et al, 1978;Kremer and Peterson, 1983;Stoddard, 1976;Wilson, 1975), (4) detailed ecological studies of the indigenous strains, and especially of those belonging to B. japonicum serogroup 123 Moawad et al, 1984;Sadowsky et al, 1987b;Viteri and Schmidt, 1987;, (5) studies on the molecular basis for competitive interaction, (6) repeated inoculation (Dunigan et al, 1984;Howieson, 1995;McLoughlin et al, 1990), and (7) host preference and restriction in nodulation (Cregan et al, 1986;Ferrey et al, 1994;Sadowsky et al, 1987b;Sadowsky et al, 1990;Sadowsky and Cregan, 1992). Strains of microorganisms which are stable members of the microbial community (members of the "local" microbial flora) appear to have a selective, competitive advantage in occupying available niches in that local environment (Atlas and Bartha 1993).…”