| Under the measures of increasing organic fertilizer and reducing chemical fertilizer,the dominant microorganisms of nitrogen metabolism were screened from the tobacco-growing soil in Guizhou,which in order to make nitrogen supplies more accord with the demand of " pre strength and post weakness" in flue-cured tobacco production,and added to organic fertilizer by multiplication to promote nitrogen mineralization and improve nitrogen utilization rate.The results are as follows:1.Eighty-five microorganisms with high nitrogen metabolic activity were isolated from tobacco-growing soils of Weining and Meitan by plate dilution method,and 12 strains with strong transformation ability were screened out by Nessler’s reagent method and ammoniating bacteria culture medium method,numbered W24,W13,W2,W4,W6,W12,W16,Z3,Z6,Z15,Z9 and Z50.They were identified by morphological characteristics and 16 S rDNA sequence analysis.Nitrogen-metabolizing microbial strains W24,W13,W2,W4,W6,W12,W16,Z3,Z6,Z15,Z9 and Z50 belong to Chryseobacterium wanjuense、Leifsonia shinshuensis、Chryseobacterium、Pantoea、Bacillus、Bacillus simple、Lysinibacillus、Bacillus simple、Aqrobacterium、Bacillus megaterium、Brevundimonas and Paenarthrobcter,respectively,through ammoniation.The strains screened had strong decomposition ability to organic nitrogen.After 72 hours of cultivation,the decomposition rates of strains W24,W13,W2,W16,W4,W6,W12,Z9,Z15,Z50,Z3 and Z6 reached 75.4%,69.9%,68.5%,59.4%,58.1%,53%,46.1%,93.4%,87.6%,49.3%,42.6% and 42.6% respectively.The strains W24,Z9 and Z15 had the strongest decomposition ability.2.The efficiency of nitrogen-metabolizing strains on nitrogen transformation is slightly different at different temperatures.Nitrogen-metabolizing microbial strains can play their own decomposition ability in organic fertilizers at 15℃,20℃ and 25℃.The effects of increasing the release rate of inorganic nitrogen in organic fertilizers are as follows: compared with the treatment without microbial agent,the amount of inorganic nitrogen conversion increases by 897.09~1688.58mg/kg,366.27~1068.05mg/kg and 550.80~1823.71mg/kg respectively.The content of ammonium nitrogen increased by 4.80~115.95mg/kg,1.29~16.93mg/kg and 0.39~5.73mg/kg,and nitrate nitrogen respectively increased by 831.20~1551.87mg/kg,360.89~1052.24mg/kg and 457.12~1820.19 mg/kg.The transformation efficiency of strains W12,Z3,Z9,W4,W13,Z6 and W24 was better at 15℃;at 20℃,the transformation efficiency of strains W6,W2,Z3,W24,Z9,Z15 and Z6 was better;at 25℃,the transformation efficiency of strains W24,W16,Z6,W4,W6 and Z3 was better.According to the difference of transformation effect of strains at different temperatures,they can be divided into temperature-sensitive strains and temperature-passivation strains.Temperaturesensitive strains are W12,W4,W13,W6,W2,W16,Z6 and Z15.Temperaturepassivation strains are Z3,Z6 and W24.3.The productivity of nitrogen-metabolizing microorganisms to organic nitrogen conversion varies with time at different temperatures.The nitrogen form transformation of organic fertilizer was mainly nitrate nitrogen form in 0-10 days and ammonium nitrogen form in 15-65 days at 15℃;ammonium nitrogen form was dominant in 5 days and 25 days;nitrate nitrogen form was dominant in 10-15 days at 20℃;ammonium nitrogen form conversion was slowly decreasing and nitrate nitrogen form was slowly increasing at 25℃.Among them,the nitrogen requirement of flue-cured tobacco growth period was most consistent: Z15 had a stable effect on nitrogen form transformation at 15℃,W2 at 20℃ and W24 at 25℃.The intensity of ammoniation decreased after 25 days at three temperatures,which was conducive to the decrease of soil inorganic nitrogen in the early growth stage of Flue-cured tobacco,and solved the problem of excessive nitrogen supply in the later growth stage.After 65 days,the intensity of ammoniation was close to that of non-application of strains,which indicating reasonable addition of ammoniated strains would not increase the loss of soil nitrogen in non-growing season of Flue-cured tobacco.4.Interaction analysis showed that the ecological adaptability of different microbial agents was different.The dominant nitrogen metabolizing strains screened at three temperatures were prepared into compound microbial agents I,II and III,which were used in Weining,Qianxi and Meitan with average annual temperature of 10℃,14℃ and 20℃ degrees centigrade respectively.The results showed that although compound microbial agents could enhance the intensity of soil ammoniation and increase the release rate of soil inorganic nitrogen,but there were significant differences in different ecological regions.Among them,Weining compound bacterium agent I had the best effect,the intensity of ammoniation and the release rate of inorganic nitrogen were 2.23 times and 61.66% respectively;Meitan compound bacterium agent III had the best effect,the intensity of ammoniation and the release rate of inorganic nitrogen were 1.91 times and 62.0% respectively;there was little difference among the three bacterium agents in Qianxi.Therefore,it is better to apply suitable compound microbial agents in different ecological regions. |
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