| Phosphorus and potassium are essential nutrients required for growth and development of plants.Soil contains high levels of phosphorus and potassium but most of them exist in the form that plants cannot absorb and utilize directly,which affects the growth and development of plants.The large-scale application of chemical fertilizer does solve the problem of phosphorus and potassium deficiency in a short time,but it does not change the soil characteristics,and will destroy the soil microenvironment,resulting in soil hardening and fertility decline.Phosphate-solubilizing bacteria and potassium solubilizing bacteria are a kind of plant growth-promoting strains that can decompose release phosphorus and potassium in soil.They can not only provide phosphorus and potassium for plants growth and development,but also promote the absorption of other trace elements by plants and inhibit the growth of pathogenic microorganisms around them.It has potential application value for agricultural production and environmental protection to prepare microbial fertilizer with efficient growth-promoting strains.Therefore,in this article,six phosphate-solubilizing bacteria with high P-solubilizing activity and five potassium solubilizing bacteria with high K-solubilizing activity were screened from the rhizosphere soil of maize.The best liquid fermentation conditions of the two strains are optimized,and the plant application experiment was carried out in different fertilization way,which provides the theoretical foundation for the industrial production and practical application of microbial fertilizer.The main contents and results of this study are as follows.Six phosphate-solubilizing bacteria with high P-solubilizing activity and five potassium solubilizing bacteria with high K-solubilizing activity were separated after preliminary screening and re-screening.The results of phosphorus solubilization ability and potassium solubilization ability showed that the phosphorus solubilizing bacteria P3 had the best phosphorus solubilization effect,and the maximum phosphorus solubilization amount reached 261 mg/L at the 5th day of culture,which increased by 249 mg/L compared with the control group and was 8 to 9 times that of the other strains.The content of available potassium in the fermentation broth of potassium solubilizing bacteria K1 reached 30.5mg/L on the 6th day,which was 24.95 mg/L higher than that in the control group.The results of p H changes in the fermentation broth during the shaking flask culture showed that the p H of the fermentation broth gradually decreased in the first few days,and it did not continue to decrease until the 4th or 5th day of culture,and tended to be stable.Among the phosphorus-releasing bacteria,strain P3 showed a more decreasing rate,which decreased to4.14 on the 4th day;among the potassium solubilizing bacteria,strain K1 showed a decreasing rate,and the p H of fermentation broth decreased to 5.16 on the 4th day.It was found that strain P3 belonged to Enterobacter and strain K1 belonged to the Agrobacterium by 16S r DNA sequencing.By single factor experiment,the culture medium and culture conditions strain of P3and K1 are carried on the preliminary optimization,the results showed that for strain P3,the best carbon source is glucose,concentration of 15 g/L,the best nitrogen source is peptone,the concentration of 4 g/L,the optimum culture condition is an initial p H 7.5,quantity of 7%,with liquid volume 80 m L/250 m L,and culture temperature 30℃,the amount of living bacterium eventually reached 8.76×10~8 cfu/m L.For strain P3,the best carbon source is glucose,concentration of 10 g/L,the best nitrogen source is peptone,concentration of 3 g/L.The optimum culture condition is the initial p H of 7.5,quantity of5%,with liquid volume 60 m L/250 m L,culture temperature 30℃,and the amount of living bacterium eventually reached 7.46×10~9 cfu/m L.The results of Plackett-Burman(P-B)test showed that glucose concentration,peptone concentration and initial p H were the significant factors affecting the number of viable bacteria in the fermentation broth of the two strains,while other factors had no significant effects.The response surface methodology test was conducted based on the P-B experimental results.The results showed that the optimal glucose concentration for liquid fermentation conditions of strain P3 was15.14 g/L,the optimal peptone concentration was 4.11 g/L,and the optimal initial p H was7.76.The maximum response value was 9.29×10~8 cfu/m L.The optimized medium composition and culture conditions were tested for three repeated tests,and the average number of bacteria in the fermentation broth was 9.18×10~8 cfu/m L,which was 98.82%of the predicted value,and increased by 2.67 times compared with the basal medium.The optimal glucose concentration,peptone concentration and initial p H for liquid fermentation conditions of strain K1 were 10.73 g/L,3.13 g/L and 7.64.The maximum response value was 8.73×10~9 cfu/m L.The optimized medium composition and culture conditions were examined for three repeated tests,and the average number of bacteria in the fermentation broth was 8.55×10~9 cfu/m L,which was 97.93%of the predicted value,and increased by2.45 times compared with the basal medium.Finally,common crops such as maize,wheat and pakchoi were selected to prepare microbial fertilizer by inoculating bacteria directly and using organic fertilizer as the carrier.The growth-promoting effects of strains P3 and K1 were verified through plant pot experiments.The results showed that the plant growth of each treatment group was significantly improved compared with that of the control group,and the microbial fertilizer with organic fertilizer as the carrier had the best growth-promoting effect.After the 7th day of corn growth,the stem and leaf length of the experimental group(T7)supplemented with microbial fertilizer mixed with two strains increased by 139.93%compared with the control group,and was 33.80%higher than that of the experimental group(T5)supplemented with organic fertilizer alone.After 14 days of growth,the fresh weight and dry weight of aboveground part in T7 group were 72.70%and 103.46%higher than those in T5 group,respectively.After 7 days of wheat growth,the fresh weight of the experimental group(T6)added with phosphate-solubilizing bacteria P3 microbial fertilizer increased by 83.55%compared with the control group and 21.22%compared with the experimental group(T4)added with organic fertilizer.After 14 days of wheat growth,the data increased to 103.32%and 52.26%.After 7 days of green vegetable growth,the fresh weight of the experimental group(T7)added with two strains of mixed microbial fertilizer was 220.00%higher than that of the control group and 136.45%higher than that of the experimental group(T4)with organic fertilizer.At 14th day of green vegetable growth,the fresh weight of the experimental group with microbial fertilizer was 534.78%higher than that of the control group,102.52%higher than that of the T4. |
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