| The application of chemical fertilizers could increase yield of crops, but it would destroy soil structure, emaciate soil fertility, ruduce production efficiency, even pollute the environment if large amount of chemical fertilizers was used for long time. Microbial fertilizers had obvious advantages in improving utilization ratio of fertilizer, increasing crop yield and protecting the ecological environment compared with chemical fertilizers. Hence, it has a great meaning for agricultural sustainable development to study microbial fertilizers deeply. Because of single function and dosage forms limitation with soybean, the objectives of this study were to screen functional strains, select non-antagonize strains into combination and then immobilize the microbial flora into particles, and evaluate the overall performances of the compound microbial fertilizer for soybean. This objectives have been achieved by the field sampling, lab analysis and pot experiment, and the results of this study might provide the theoretical basis for application and development of new-type microbial fertilizers for soybean.1.Collected field samples, isolated and screened strains and tested their performances and identified:(l) Three rhizobia strains with higher nodulation and nitrogenase activity were obtained, which were R12, R6and R18. R12was superior to the reference strain USDA110in many respects, for example, the number of nodules, nodule dry weight, nitrogenase activity, and growth promotion for plants. R12also exhibited organic phosphorus solubilization activity. Neither R6nor R18has phosphate solubilization activity. Other characters of R6and R18were approaching to USDA110. All of them were identified as the genus Rhizobium. Among them, R12identified as Rhizobium etli, and R6and R18as different strains of Rhizobium tropici.(2)Two bacterial strains S7and S1with higher inorganic and organic phosphorus solubilization activity were obtained. The amout of dissolving insoluble phosphates of S7and S1was respectively174.8mg/L and167.3mg/L, which was5.87%and1.33%higher than that of reference strain1203. Decomposition amount of lecithin of S7and S1was respectively49.33mg/L and54.82mg/L, and which of the reference strain1203was52.93mg/L. In general, S7preferred to dissolving inorganic phosphorus, and S1preferred to decomposing organic phosphorus. The total amout of dissolved inorganic and organic phosphorus of S7and S1was2.80%and1.88%higher than that of the reference strain1203, respectively. S7was identified as the genus Bacillus, and S1as the genus Pseudomonas.(3) One strain marked C1with high activity of decomposing soil potassium mineral were gotten. It could release potassium21.31mg/L into solution from soil potassium mineral when cultured seven days. The amount of decomposing soil potassium mineral of C1was34.28%higher than that of the reference strain L-K. C1was identified as Bacillus mucilaginosus of the genus Bacillus.2.Selected the combination of strains in good performances by the antagonistic and growth relationship test for three types of strains, optimized the condition of culture and the medium component, and improved the method of culture.(1)R12, S7and C1could coexist. R12-S7and R12-C1could promoting growth each other while mixed culture. However, S7-C1was in relationship of independent of habitat.(2)Optimized medium formula was:mannitol10g, yeast extract1.0g,(NH4)2SO40.5g, K2HPO40.5g, KC10.2g, MgSO4·7H2O1.0g, MnSO40.004g, CaCO35.0g, FeSO4·7H2O0.003g, CaCl20.1g, potassium feldspar powder2.0g, rock phosphate5.0g, lecithin2.0g, Rh solution4.0mL, distilled water1L. The optimal order of inoculation was R12â†'S7â†'C1, the interval was12h. The optimal pH of mixed culture was7.0and culture temperature of mixed culture was28℃.3.Immobilized the flora. Studied the influence of embedding material on embedding operation and basic characters of embedded particles, and compared the bacterial stress resistances in the different dosage forms:(1)The basic ingredients composition was SA3.0%-PVA3.0%. Under the composition, operability and spheronization, as well as mechanical strength, mass transfer performance, embedded rate, the number of viable cells and their proliferation times were better than other ingredients composition.(2) Under the optimized embedding medium [SA3.0%-PVA (2.5%-3.0%)-(SiO24.0%-CaCO30.3%)], operability, spheronization and mass transfer performance were clearly inproved. The particles presented regular ball with diameter of3-4mm, the mechanical strength was53.4-59.6g/g, and the embedded rate was91.4-94.3%. After72h proliferation, the number of viable cells reached magnitude1011per gram of the embedded particles. Proliferation multiples was500times more than no embedded strains, and the rate of releasing viable cells was90%higher than no embedded strains.(3) The salt tolerance, the acid-base tolerance, the drought tolerance, the hot tolerance and the drug tolerance were stronger than no embedded strains.4.Evaluated the effects of the microbial agents and ensured its application methods by the pot trial in which chemical fertilizer, peat inoculant and the embedded particles were respectively used.(1) The yield and quality of soybean were improved, the amount of nodulations, nitrogen fixation and nutrient absorption were increased, and the biological characteristics of plants, available nutrient supplication and biological environment of soil were better by using the microbial agents than control treatment.(2) The effects of applying the the microbial agents combined with chemical fertilizers were better than that of only using the same amount of chemical fertilizers or t the microbial agents.(3) That the efficiency of combining the embedded particles and half amount of chemical fertilizers was better than that of full amount of chemical fertilizer treatment. But the interaction effects were weakened while increasing the amount of chemical fertilizers continuely.(4) The effects of the embedded particles were always better than peat inoculant whether used alone or mixed with chemical fertilizers. |
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