| This study was based on an eight years long-term fertilized rice-wheat rotation system in south of Jiangsu province.Four treatments including no fertilizer control(CK)and three pure pig manure composting treatments(OF):1500 kg/ha organic fertilizer(OF1),3000 kg/ha organic fertilizer(OF2)and 4500 kg/ha organic fertilizer(OF3).This study aimed to explore the effects of pure organic fertilization on 1)wheat yield;2)soil physical and chemical properties and soil enzyme activity;3)functional microorganisms of the nitrogen cycle;4)soil bacterial community structure,diversity and compositions.The main research results are obtained as follow:1.Compared with CK,the application of different amounts of organic fertilizers could increase the wheat yield,while OF1 251.85 kg/ha,OF2 607.41 kg/ha,OF3 459.26 kg/ha higher than CK,respectively.OF2 had the highest yield of wheat,33.47%higher than CK,followed with OF3.The yield of wheat by fertilization was higher than that of non-fertilization.2.Compared with CK treatment,organic fertilizer treatments had the significantly higher content of total nitrogen(TN),and OF3 had the highest content of TN in four stages,about 1.39 g/kg.Soil organic matters(SOM)of organic fertilizer treatments were higher than that of CK.Notably,OF3 had the highest SOM content of 30.11 g/kg than the other three treatments across the four wheat growth stages.The contents of available potassium(AK)and available phosphorus(AP)of organic fertilizer treatments was significantly higher than that of CK.No significant difference of available nitrogen(AN)was found between the four treatments.3.The organic fertilizer treatments significantly improved the activity of urease when compared with CK,and the urease activity gradually increased following the wheat growth stages.The highest enzyme activity was found in OF3 in June.The microporous plate fluorescence method was used to detect the activity of seven extracellular enzymes and the activity gradually increased with the increasement of applicated organic fertilizer amounts.4.The results of real-time PCR showed that the enrichment of nifH gene in soil was less affected by the application of organic fertilizer,and the growth of wheat caused dynamic reduction of nitrogen-fixation bacterial abundance.The application of organic fertilizer could improve the abundance of AOA,AOB and nirS gene,stimulate the activity of soil microbial and promote the nitrogen cycle.Fertilization and crop growth stages were the two most important factors in affecting soil microbial activity.5.Illumina MiSeq high-throughput sequencing was used to sequence the 16S rRNA V4-V5 region of soil bacteria,and the results showed that pig manure compost organic fertilizer significantly improved the abundance of bacteria in the soil.Wheat growth stage was the primary factor that caused the changes of soil bacteria abundance;the application of organic fertilizer can improve the richness and evenness of bacterial communities.Application of organic fertilizer also significantly improved the diversity of bacterial communities,facilitated the construction of more stable bacterial groups.The bacterial community structure was significantly affected by organic fertilizer.The application of organic fertilizer changed the soil bacterial community structure by influencing soil nutrient contents.Fertilization and crop growth stages as two crucial factors affected the microorganisms.In conclusion,applying appropriate amount of organic fertilizer can improve wheat yield to a certain extent.The application of organic fertilizer could increase SOM and TN contents,which could provide soil with more nutrients than non-fertilization.Organic fertilizer could sustain the stability of soil enzyme,meanwhile,promoted the activity of urease.The application of organic fertilizer could change the numbers of soil functional microorganisms,improve the diversity of bacterial communities,and shape more stable bacterial community flora. |
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