Effects of microbial inoculants on soil microbial diversity and degrading process of corn straw returned to field

Returning crop straw to field is one of the common methods to improve soil organic matter and achieve sustainable development of agriculture. However, corn straw is composed mainly of highly polymerized lignocellulose with a high carbon to nitrogen (C:N) ratios, and it degrades slowly in the field. The difficulty of straw degradation in a short time hampers the seedling growth and farming operation. In some place farmers burn crop straw after harvest in order to immediately sow the next crop, which contributes to environmental pollution and greenhouse gas emissions. Acceleration of straw degradation in the field is urgently needed, and utilization of microbial inoculants is a safe and effective method. To reveal the effects of microbial inoculants on degrading process of corn straw and soil microbial diversity after straw was returned to the field, an incubation experiment was carried out in the field. The experiment was conducted in the winter Wheat-maize rotation of the high yield area located around Hebei Academy of Agriculture and forestry Sciences, North China Plain from Oct 2009 to Apr 2010, and three different microbial inoculants (ND, NK and NS) were used in this study. The residual weights and C/N ratios of corn straw in different inoculated treatments were measured to estimate the degrading enhancement of the three inoculants at four different sampling times of 15d, 25d, 145d and 160d. The results showed that the degradation of corn straw could be enhanced by inoculation in early period (first 25d), and residual percentages of corn straw in ND, NK and NS were 14.3%, 7.7% and 1.6% lower than that in CK, respectively. C/N ratios of corn straw in inoculant treatments decreased more rapidly than that in CK, and the decreases were also showed up in early stage. In order to find the effects of microbial inoculants on soil microbial diversity, V3 region of bacterial 16S rDNA and Dl region of fungal 26S rDNA gene sequences were detected by denaturing gradient gel electrophoresis (DGGE), and Cluster analyses based on the band similarity in migration and intensity between lanes were used to understand the distance of each lanes. Furthermore bands of the three inoculants were used to study the relationships between inoculation and soil microbial diversity, and dominant bands of bacteria and fungi were excised from DGGE gels and sequenced to get further microbial information. The results showed that most bands from inoculants, which matched to Bacillus fusif