Effect of Rhizobia and PGPR co-inoculant on soybean characteristics and soil enzyme activities

【Objective】 The effects and mechanism on single inoculant of Paenibacillus mucilaginosus and Bradyrhizobium japonicum have been widely characterized, but few on the that of co-inoculant of them. A field experiment was carried out to reveal the effects of rhizobia and PGPR on soil enzyme activities, soybean growth and nodulation. 【Methods】 Five differents with fertilization measures in this field experiment were designed by T1(CK), T2(inoculant of Paenibacillus mucilaginosus 3016), T3(inoculant of Bradyrhizobium japonicum 5136), T4(co-inoculant of P. mucilaginosus 3016 and B. japonicum 5136) and T5(the regular fertilizer dose). Soil enzyme activities, soybean growth characteristics at different stages of soybean and the nodule occupancy of B. japonicum 5136 were studied. BOX-PCR was used to analyze the nodule occupancy of B. japonicum 5136.【Results】 1) At maturation periods, soybean growth traits, branch number per plant, seeds per plant, harvest index and yield in the T4 treatment were the highest, and respectively increased by 11.3%, 9.7%, 41.0% and 9.3% relative to those in the T1 treatment. The empty pods per plant in T4 treatment was the lowest, and was 44.0% lower than that in the T1 treatment, indicating the prosperous effect of co-inoculant on improving soybean traits. 2) The nodule occupancy of B. japonicum 5136 in the T4 treatment was 25.4%, and 8.0% higher than T3 treatment. Nodules per plant, nodule dry matter per plant in the T4 treatment exhibited the highest values during the flowering and podding periods, and increased 41.6% and 47.1% relative to thosed in the T1 treatment, suggesting that P. mucilaginosus 3016 was helpful to nodulation of B. japonicum 5136. 3) P. mucilaginosus 3016 and B. japonicum 5136 could increase the activities of catalase, urease and invertase in soil. During maturation periods,the activity of these enzymes inT4 treatment was the highest, and were 12.9%, 8.9% and 9.4% higher thanT1 treatment, respectively. 4)The soil enzyme activities were significantly and positive correlated(P0.01) or positive correlated(P0.05) with harvest index, and catalase activity was positive correlated with yield. Nodules per plant and nodule dry matter per plant were significantly positive correlated with harvest index and invertase activity, respectively, and was positive correlated with yield. 【Conclusions】 Co-inoculant of P. mucilaginosus 3016 and B. japonicum 5136 could significantly increase soybean branch number per plant, seeds per plant, harvest index, the yield and nodule occupancy, and reduce the empty pods per plant, and increase enzyme activities, indicating that the co-inoculant of P. mucilaginosus 3016 and B. japonicum 5136 is an optimal application measure in soybean cropping system.