A study of the effect of soil-available N and indigenous rhizobial population on the growth and yield of soybean and prediction by models of the necessity to inoculate

Abstract

The effect of the initial population of Bradyrhizobium japonicum and soil N availability indices on inoculation response of soybean was studied. At first, in the field experiment, the influence of the size of the indigenous rhizobial population on the soybean inoculation response was investigated in a randomised complete block design (RCBD) with three replicates and three inoculation levels and one N treatment of 100 kg ha−1. In a greenhouse experiment, eight soils with different numbers of indigenous soybean rhizobia, and N mineralisation potentials were used. For each soil sample, a RCBD with four replicates and four treatments of one inoculation and two N levels and a control treatment were used. Results showed that in soils with high rhizobial populations or available N, inoculation had no effect on the growth indices of soybean. Inoculation increased shoot dry matter, seed yield and total N uptake in soils poor in indigenous rhizobial populations and N content. Based on the experimental data some models for predicting the necessity for inoculating soybean were developed.