Multistrain vs. Single Strain Rhizobium japonicum Inoculants for Early Maturing (00 and 000) Soybean Cultivars: N₂Fixation Quantified by ¹⁵N Isotope Dilution¹

Abstract

Early maturing soybean cultivars (groups 00 and 000) adapted to western Canada are now available but since the soils contain no indigenous Rhizobium japonicum, it is important to determine if strains selected for efficient N2fixation with American soybean cultivars are also efficient with Canadian cultivars and if single strain are superior to multistrain inoculants. Accordingly, a 2‐year evaluation was made of the effect of up to eight single strains and two commercial multistrain combinations of R. japonicumgranular inoculants on maturity, seed yield, oil and protein content, and N2fixation (as determined for the first time by 15N isotope dilution) for three promising soybean lines. Rhizobium japonicumstrains 61A148 (USDA 142) and 61A118 (USDA 138) were consistently superior in N2fixation with all soybean cultivars, resulting in seed yields and seed protein higher than those of the other strains. Strain 61A101 was consistently an inefficient N2fixer. These differences in efficiency between strains were not related to documented ability to take up H2evolved by nitrogenase because, although strain 61A148 is considered Hup+, strain 61A118 is Hup–. Several strains resulted in percent plant N derived from the atmosphere exceeding 50% with N2fixed as high as 151 kg N ha−1for strain 61A148 on King Grain line X005. However, over all strains, Maple Amber was superior for supporting N2fixation, averaging 91 kg while X005 had 83 kg and Maple Presto 60 kg N fixed ha−1. Line strain combinations resulting in lower levels of N2fixation assimilated more soil N such that total N yields averaged over lines and strains were generally similar. These strains selected for U. S. soybean cultivars are also acceptable for Canadian soybeans. Interstrain competition occurred with one multistrain inoculant, to the detriment of plant yield. A commercial mix containing four strains (61A101, 61A118, 61A124, 61A148) had low N2fixation similar to that of strain 61A101. This suggested that strain 61A101 was highly competitive and may have formed a majority of the nodules thereby excluding the highly efficient strains 61A118 and 61A148. However, a new commercial mix containing three strains which were clones of 61A101, 61A118, and 61A124 did not exhibit any detrimental interstrain competition. Thus, the new multistrain soybean inoculant can be recommended for Canadian soybean cultivars.

Nitrogen fixation(N-15 dilution) with soybeans under Thai field conditions. III. Effects of Bradyrhizobium japonicum strains and herbicides in northeast Thailand.

“…Preparation of the plant material, Kjeldahl digestions and mass spectrometer determination of N-15 in the plant material are as described by RENNIE and DUBETZ (4). Isotope terminology and calculations used are according to RENNIE et al (16).…”

“…is beneficial in the tropical soils of southeast Asia (1)(2)(3). The benefits depend greatly on the selection of appropriate bacterial strains, since bacterial strain-soybean cultivar specificity has been found in many cases (3)(4)(5)(6). Native populations of Bradyrhizobium japonicum cannot be relied upon to supply adequate amounts of N for commercial soybean production since they vary considerably in their competitiveness and N2-fixing abilities (7,8).…”

SURVIVAL OF Bradyrhizobium japonicum IN CANADIAN PRAIRIE SOILS

“…At maturity, the seed yield and protein content of the noninoculated treatment were significantly lower than that of the inoculated treatments (Table 2) Rennie and Dubetz (1983) and Bailey (1988). Rennie and Dubetz (1983) When soils on which inoculated soybean was grown were stored for 5 mo in a frozen (Table 48) or "dried-out" (Table 4C) …”

Diversity of symbiotic rhizobia resident in Canadian soils

“…In Canadian prairie soils, multi-strain and single strain inoculants were shown to be symbiotically effective with western Canadian soybean cultivars (Rennie and Dubetz 1984). Balley (1989) reported that inoculant strains increased soybean seed yield and protein content, but uninoculated soybean grown 1 yr later in the same plots were not nodulated, suggesting that the inoculant strains did not survive over winter.…”