Improvement Of Soil Aggregates And Biological Activity By Fertilization And Inoculation Of Extracellular Polymeric Substances Producing Microbes

Soil aggregate structure is the basic unit of soil structure and is the foundation of soil fertility.The formation and stability of soil aggregate structure is effectted by all kinds of cementing material in the soil.Microorganisms and their extracellular polymeric substances have important roles on the formation of soil aggregates.In addition,the formation of water stablity soil aggregates must depend on the soil organic matter.The good soil aggregate structure is very important for sustainable development of agriculture.The research studied the effects of bacteria and fungi which producing exopolysaccharide,and organic fertilizer on improving soil aggregate structure.The research results were as follows:1.Two bacterial strains named strain 21 and strain G1 which can produce extracellular polysaccharide were isolated from soil.Through morphological observation,physiological and biochemical experiments,16S rRNA gene sequence analysis,strain 21 was identified as Microbacillus and strain G1 was identified as Bacillus megaterium.The strain 21 grew best at 30?,initial pH 7,sucrose as carbon source.The strain G1 grew best at 30 ?,initial pH 7,sucrose,glucose and starch as carbon source,yeast powder,peptone and beef extract as nitrogen source.2.The effect of inoculating bacterial strains 21,strain G1 or fungi strain T037 combined with application of pig manure or herb residues compost respectively on the soil aggregate structure in the soil culture experiment.The results showed that inoculating three microbial strains above respectively combined with application of dried pig manure or herb residues compost could increase the contents of macroaggregates,reduce the contents of aggregates less than 0.25mm by 2.79%?43.56%.In addition,the treatment applied with dried pig manure had a more significant effect on increasing the contents of large aggregates in the soil than herb residues compost.Inoculating three microbial strains above respectively combined with application of dried pig manure or herb residues compost also increased the richness of soil microorganisms in different size of aggregates,the biger the aggregates size,the richer the abundance of microorganisms.Inoculating three microbial strains above respectively combined with application of dried pig manure or herb residues compost changed the community structure of soil bacteria to some degree,changed the relative abundance of bacterial phylum and genus.There was no significant difference of bacteria community structure in different size of aggregates.The treatment applied with pig manure and herb residues compost could effectively increase soil organic matter,total nitrogen,available phosphorus and available potassium contents,also increse the activities of sucrase and urease in soil.The smaller the aggregates size,the lower the activity of invertase and urease in soil.The treatment applied with pig manure had a more significant effect on soil organic matter,total nitrogen,available phosphorus and available potassium contents than herb residues compost.Inoculating three microbial strains above respectively combined with application of organic fertilizers had a more significant effect on increasing contents of larger aggregates in the soil than only application of organic fertilizers.Inoculating three microbial strains above respectively could increase the contents of soil polysaccharides,and the the biger the aggregates size,the higher the content of soil polysaccharides.3.The soils with different treatments above for one year were used to cultivate the tomato through pot experiment.It was found that the soil after treatment by inoculating three microbial strains above respectively combined with application of organic fertilizers could effectively promote plant growth,significantly increased plant height,stem diameter,shoot fresh and dry weight,and root fresh and dry weight.Otherwise,the treatment applied with pig manure could increase the chlorophyll content of tomato leaves.