The Effects Of Slime-forming Bacteria On The Formation Of Soil Water-stable Aggregates

Soil aggregates are normally considered as the basis of soil fertility. Good soil structure is important for sustainable development of agriculture. The soil polysaccharides which can be produced by slime-forming bacteria play a important role in the formation of soil aggregates. In order to study the effect of slime-forming bacteria on the formation of soil water-stable aggregates(WSA), the bacteria were isolated from some samples according to the slime production and effect of their fermentation on the formation of >0.25mm soil WSA. The samples were soil crust collected from Inner Mongolia, the corn growth field soil in the Scientific Park of China Agricultural University, and earthworm faeces. Subsequently through the soil(sterilized or not) culture, the effects of carbon source and soil structure on the isolated bacteria growth and formation of WSA were studied by wet sieve and chloroform fumigation extraction methods. The main results were as following:According to slime production, we isolated 17 slime-forming bactreria. 4 strains, namely No1, No10, No15, Nol6 were selected, as their fermentation liquid significantly promoted the formation of >0.25rnm soil WSA. Nol was Bacillus sp, and Nol5, Nol6 were Pseudomonas sp.The secondary metabolites of the bacteria rather than bacterial cells played more important role in promoting soil aggregate formation.The isolates could grow and multiply in the sterilized soil.The stimulating effects of isolates on soil aggregates changed with supplying different organic materials. The effect was the best when supplying with sucrose. And the content of >0.25mm soil WSA was more than 80%. The highest >0.25mm WSA content were 75% and 60% with wheat straw and maize straw. Supplying with leonardite almost had hardly effect. And the highest >0.25mm WSA content was 28%.The results showed that supplying wheat straw could promote the formation of >0.25mm soil WSA. The contribution of straw to the formation of >0.25mm soil WSA was 87% in the soil with less clay, and 58% in the soil with more clay. If the soil was not sterilized, the inoculation of isolates had no effect on soil WSA and soil microbial biomass carbon.