Physicochemical And Microbial Properties In The Process Of Biochemical Humic Acids Producing By Straw Fermentation

Straw is one of the richest renewable agricultural resource in China, and are usually used as organic fertilizer after fermentation. In the recent years, the straw has been used to produce the biochemical humic acid by fermentation, and which can reduce environmental pollution, and improve the straw resource utilization, and product had high added-value. In this paper, four treatments, i.e. straw section+urea (treatment I), straw powder+urea (treatment II), straw section+cow dung (treatment III), straw powder+cow dung (treatment IV), were used to ferment and produce biochemical humic acid, and the physical and chemical properties, degradation of straw component, humus formation and the microbial community was studied during the fermentation process, and the results were as follows.During the fermentation, the physical and chemical property of4treatments was studied. The results showed that the color of compost material changed from yellow or yellow brown into dark brown gradually; The maximum fermentation temperature reached to74℃, and the high temperature stage (≥55℃) was sustained for25d; The pH value of fermentation material decreased at the beginning of fermentation, and then followed by rising, and the final pH value was7.92-8.08at the end of fermentation.The mesophilic and thermophilic microbial quantities in defferent compost materials were as the seriation:bacteria＞actinomycete＞fungi. At late fermentation stage, the quantity of mesophilic bacteria was between1.10×109～1.32×109cfu·g-1; and the quantity of mesophilic actinomycetes was between1.10×106～1.22×106cfu·g-1; the amount of mesophilic fungi was4.33×103～5.64×103cfu·g-1.The amount of thermophilic bacteria was between2.99×108～4.6×108cfu·g-1; the amount of thermophilic actinomycete was7.81×105～8.21×105cfu·g-1. At the early fermentation stage, there was no fungus in the compost straw detected. On the30th day, fungi quantity reached the highest, and was1.25×104～1.52×104cfu·g-1, and the quantity was2.47×103～5.00×103cfu·g-1when fermentation finished.The cellulose, hemicellulose, and lignin content of different treatment materials decreased with the extension of fermentation time. The cellulose content decreased from29.61%～31.99%at beginning to1.24～1.96%in the end; and the hemicellulose content varied from24.16%～27.74%at early to5.97%～6.42%in the end; the lignin content reduced slightly, and changed from25.28%～25.93%at early to24.76%～25.11%.Water-soluble component content of compost material increased at first and then decreased, and the value increased from4.3%～9.8%to17.5%～18.1%, and decreased to9.8%～10.9%. The C/N ratio of compost matter decreased from31.7～32.8to13.9～14.7; and humus content increased from55.6g·kg-1～81.3g·kg-1to117.3g·kg-1～125.8g·kg-1; humic acid content increased from12.7g·kg-1～34.4g·kg-1to81.3g·kg-1～85.8g·kg-1; however, the fulvic acid content decreased from38.2g·kg-1～41.3g·kg-1to29.9g·kg-1～33.4g·kg-1; the H/F ratio increased from0.31～0.83to2.49～2.70.The DGGE bands were cloned and sequenced; the results revealed that the dominant bacteria were Ochrobactrum sp., Acinetobacter sp., Pseudomonas sp., and uncultured Flexibacteraceae bacterium; the others belonged to uncultured bacterium. These bacteria mainly belong to γ-proteobacteria, α-proteobacteria and bacteroidetes at the classification level of phylum.In late fermentation stage, the microbial community in compost matter of the straw section+urea (treatment I corresponds to S1) and straw section+cow-dungs (treatment Ⅲ corresponds to S2) was analyzed using the454pyrosequencing method. The results suggested that the bacterial groups were very different at the classification level of phylum, class, order, and family and genus. At the level of phylum, the predominant bacteria groups of the two samples mainly belonged to Proteobacteria and Bacteroidetes. The ratio of Proteobacteria in sample S1and S2was31.62%and35.81%, and the ratio of Bacteroidetes in S1and S2was27.41%and35.29%. Furthermore, the proportion of bacteria belong to Firmicutes, unclassified Bacteria, Tenericutes in S1was18.15%,8.80%and7.28%; but the proportion of bacteria belong to Firmicutes, unclassified Bacteria and Planctomycetes in S2was3.43%,9.63%and7.06%.Analysis of454pyrosequencing suggested that there were no common bacteria groups existed in the top10OTUs in S1and S2, which revealed that, adding cow manure and urea into straw, the bacteria groups involved in the fermentation were influenced heavily, and the dominant bacteria groups were completely different. The results indicated that, when applying the different nitrogen source (cow dung and urea) in the straw, though the fermentation parameters such as fermentation temperature etc., degradation rate of straw, decomposing and the humus content and humic acid components had not significant differences, the microbial groups were quite different, and the bacteria diversity index of fermentation materials adding urea was higher than that adding cow manure during the processing of fermentation. The results revealed that the microbial communities participating in humic acid formation and transformation were diverse in different environments.