Application of Bradyrhizobium japonicum and phosphorus fertilization improved growth, yield and nodulation of soybean in the sub-humid hilly region of Azad Jammu and Kashmir, Pakistan

Two separate experiments (pot and field) were conducted to examine the response of soybean to Bradyrhizobium japonicum and phosphorus (P) fertilization. Different treatments were i) Rhizobium strains (0, S377, S379, and the mixture of S377+S379 i.e. S-0, S-1, S-2, S-3,); ii) phosphorus (field only, 0, 50, 100 kg ha(-1)i.e. To, T-1, T-2) and iii) two soils (pot only) i.e. autoclaved (A(1)) and non-autoclaved (A(0)). A soybean cultivar NARC-1 was tested for estimating growth traits, nodule number and mass, root development and yield traits. In the pot experiment, total number of nodules both in the A(0) and A(1) were negligible but increased significantly following the application of Bradyrhizobium japonicum. In the field experiment, number of nodules increased from 6 in the control treatment without strains to a maximum of 86 in S3T1. Shoot dry weight increased significantly from 11.8 g plant(-1) in the control soil to 15.6 g plant(-1) in S3T1. Root length was increased but root mass was unaffected. Soybean seed yields ranged between 615 and 1003 kg ha(-1) against 543 kg ha(-1) in the control soil indicating a maximum of 85% increase over control. Shoot dry weight and seed yield had significant correlation with nodulation (R-2=0.91). The results of experiments revealed significant positive effects of rhizobium inoculation and P fertilization on growth, nodulation and yield of soybean and, generally, mixture of strains (S-3) was more effective than the strains S-1 and S-2. Results also indicated that high application of P (100 kg P2O5 ha(-1)) reduced the efficiency of inoculants for nodule mass and seed yield.