Effect of Soil Physical Properties on Soybean Nodulation and N_2 Fixation at the Early Growth Stage in Heavy Soil Field in Hachirougata Polder, Japan (Plant Nutrition)

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We studied the effect of the soil physical properties on soybean nodulation and N_2 fixation in the heavy soil of an upland field (UF) and an upland field converted from a paddy field (UCPF) in the Hachirougata polder, Japan. Seeds of the soybean cultivar Ryuho were sown in each field with or without inoculation of Bradyrhizobium japonicum A1017. The soybean plants were sampled at 35 (V3) and 65 (R1) d after sowing (DAS), and then nodulation and the percentage of N derived from N2 fixation in the xylem sap were determined. The soil physical properties were different between UF and UCPF, especially the air permeability and soil water regime. Nodule growth was restricted in UCPF irrespective of rhizobial inoculation, though rhizobial infection was not inhibited by the unfavorable soil physical conditions. Soybean plant growth was closely related to the nodule mass and N_2 fixation activity, and the inoculation of a superior rhizobium strain was effective only at 35 DAS. These results indicate that soybean nodulation and N_2 fixation was considerably affected by the physical properties of heavy soil, and that it is important to maintain the N_2 fixation activity and inoculate the soybean plants with a superior rhizobium strain at a later growth stage in order to increase soybean production in heavy soil fields.
社団法人日本土壌肥料学会の論文