| The excessive use of chemical fertilizers in agricultural production result in decline of soil fertility and environmental problems. Microbial fertilizers have attracted considerable attention of researchers due to their growth-promoting properties, improving yield and quality of crops, reducing the use of fertilizers, soil improvement, environment protection, etc. Paenibacillus mucilaginosus and Bradyrhizobium japonicum, as the production strains of microbial fertilizer, could release mobile nutritional ions, soluble content of K, P and symbiotic nitrogen fixation.Until now, there have been many researches regarding effects and mechanism on single inoculant of P. mucilaginosus and B. japonicum, but those of co-inoculant were scarcely ever studied. In order to reveal the effects of co-inoculation of rhizobia and PGPR on soybean growth, nodulation, soil fertility and soil microflora, a field experiment with five different fertilizing measures was carried out, including T1(the control), T2(inoculant of P. mucilaginosus3016), T3(inoculant of B. japonicum5136), T4(co-inoculant of P. mucilaginosus3016and B. japonicum5136) and T5(the regular fertilizer dose). The results showed as follows.(1) As for soybean growth traits, during maturation periods, branch per plant, seeds per plant, seeds weight per plant and yield under T4were all the highest, which were11.3%,9.7%,12.8%and9.3%higher than that under T1, respectively. While the empty pods per plant was lowest, which was44.0%lower than T1. The harvest index under T4was up to0.55,41.0%higher than that under T1. So, co-inoculant could improve soybean traits.(2) In terms of the quality of soybean, N, P, K content in seeds, stem and leaves under T4were in a high level, especially K in seeds, N and P in stem and leaves, which were increased by5.7%,9.3%and38.5%, respectively. So, co-inoculant could improve soybean quality.(3) In the respect of soybean nodulation and nitrogen fixation, soybean nodule characters in flowering and podding stage showed that, the nodule occupancy of B. japonicum5136under T4was25.4%, which was8.0%higher than that under T3. And nodules per plant, nodule dry matter per plant under T4were also the highest during the flowering and podding periods, with a rate of41.6%and47.1%higher than that under T1. So, P. mucilaginosus3016was helpful to B. japonicum5136for nodulation.(4) As far as soil fertility to be concerned, both microbial fertilizer and chemical fertilizer could improve soil total N, available P, available K and organic matter to some extent, but the former was more persistent and had a less effect on soil pH. The soil fertility under T4was best, with a higher rate of6.5%、43.7%、8.5%and15.5%in soil total N, available P, available K and organic matter than that under T1. So, co-inoculant could improve soil fertility.(5) When comes to soil enzyme activity, P. mucilaginosus3016and B. japonicum5136could increase the soil catalase, urease and invertase activities. And T4was the best with an increasing rate of12.9%,8.9%and9.4%than that under T1, respectively. So, microbial fertilizer was beneficial to soil enzyme activity.(6) Iln the case of microflora, co-inoculant could increase soil microbial quantity, enrich the bacteria and actinomycete and inhibit the quantity of fungi, which made a change of soil to "bacteria type" from "fungus type", reduced fungal diseases and enriched the soil microbial community structure.(7) Correlation analysis indicated that, available P, available K, organic matter, catalase and urease activities were significantly positive correlated with harvest index, respectively (p<0.01). Nodules per plant and nodule dry matter per plant were significantly positive correlated with empty pods per plant, seeds per plant, harvest index and invertase activity, respectively, and was positive correlated with yield (p<0.05). As for soil microorganisms, the actinomycetes were higher correlated with soil fertilities. There was a good correlation between soil fertilities, especially available P, available K, invertase and catalase activities, with soybean nutrient.Above all, co-inoculant of P. mucilaginosus3016and B. japonicum5136could significantly increase soybean branch per plant, seeds per plant, seeds weight per plant, nodule occupancy and the yield, reduce the empty pods per plant, improve N, P, K content of seeds, stern and leaves, increase soil fertility and soil microflora. That may be an optimal fertilizing measure and the results were of great realistic and theoretical value on enriching species resources and production of microbial fertilizers. |
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