Effectiveness of Commercial Rhizobial Inocula on the Growth and Seed Yield of Improved Soybean Varieties on Upland Alfisol in East Java

Abstract

Bradyrhizobium spp. could largely provide nitrogen required for soybean growth via their symbiosis. The amount of N conferred is determined by the genotypes of host plant and Bradyrhizobium spp. as well as environmental factors. The field experiment was undertaken to study the effectiveness of Bradyrhizobium spp. on some improved soybean varieties on the upland Alfisol in Probolinggo, East Java, Indonesia. The inoculation treatments and soybean varieties were combined factorially and arranged in a split plot design. Each factorial treatment was replicated 3 times. The parameters measured were the number and weight of nodules, plant height, plant dry matter weight, and seed yield per ha. Field inoculation with commercial rhizobial inocula increased plant height and nodule numbers of soybean at 3 weeks after planting (WAP), and the inoculation effect was the same among soybean cultivars tested. The soybean genotypes used in our field study did not affect the nodulation by indigenous and inoculated rhizobia at 3 and 6 WAR Nodule formation by indigenous and inoculated rhizobia is not dependent on plant genotypes. Thus all plant genotypes used in the present study are compatible with indigenous and inoculated rhizobia in nodule formation. Plant vegetative growth, measured as plant height and plant dry matter weight, was promoted through inoculation. Seed yield was significantly affected by the soybean genotypes only. Since the productivity of inoculated soybean was similar to that of un-inoculated one, it is indicated that the upland Alfisol soil tested contains indigenous rhizobia which are as effective as the commercial rhizobial inocula.