Abstract: Background, aim and scope Straw is the mature crop stems and leaves (ear), usually refers to cotton, wheat, corn, rice and other crops remaining after harvest seeds. Straw is rich in nitrogen, phosphorus, potassium and organic matter for more than 50% photosynthetic products exist in it. If these agricultural solid wastes can not be effectively used and processed, it will not only lead to waste of resources, but also cause environmental pollution and other issues. China is the world's largest cotton (Gossypium hirsutum L.) production country. Cotton acreage, cotton yield and cotton output are ranked first in the world, cotton production accounts for about 1/4 of the world's total output. Cotton straw returning to the field is still the main treatment method, but the cotton straw returned to the field could not be degraded quickly, which seriously affected the sowing and seedling emergence of cotton in the following year. How to deal with and quickly break down the cotton straw into the field has become an urgent problem to be solved. Based on previous research work, an antagonism test is used to test the possibility of culture compound between white rot fungi and Sporotrichum thermophile; then the optimal condition for compound inoculants degradation of cotton straw was selected by orthogonal pot experiment; and finally the effect of compound microorganism based on orthogonal experiment results was verified in a field test. Material and methods The operation method of antagonism test is as following: the two strains were all picked a small colony in PDA culture medium plate, inoculated around 3 cm distance of the center point, cultured 5 d at 30℃, carefully observe the strains are mutually inhibited mycelial growth and spore formation and colony growth. When two strains of white rot fungi and Sporotrichum thermophile not mutually inhibit the mycelium growth, there was no antagonistic reaction between the strains. If the inoculated strains were separated and there was a clear gap between the two strains, this means these two kinds of microorganisms have the antagonistic phenomenon. L9(34) orthogonal design was used to screening out the optimal experiment conditions of the degradation of cotton straw under different temperature, N content, microbial strain and water ratio conditions. Cellulose, lignin and acid detergent fiber (ADF) were analyzed after a 40 d degradation period to evaluate the cotton straw degradation degree. Based on the orthogonal experiment result, the actual effect of the compound white rot fungi and Sporotrichum thermophile in the field of cotton straw decomposition was studied at the optimal conditions. Cellulose, lignin and acid detergent fiber (ADF) were analyzed by the Van Soest method. Cotton straw degradation was tested by the difference weight method during the experimental period. Result The results showed as follows: (1) White rot fungi and Sporotrichum thermophile were not mutually inhibit the mycelium growth, there was no antagonistic reaction between the strains and the compound white rot fungi and Sporotrichum thermophile could be used to degradation cotton stalk. (2) According to L9(34) orthogonal test results, considering temperature, amount of N, strain type and ratio of material to water on cotton straw lignin, cellulose and acid detergent fiber degradation, the optimal combination of indoor conditions to degradation of cotton straw is temperature at 45℃, the amount of N at 3%, the ratio of material to water at 1/2 and compound white rot fungi and Sporotrichum thermophile. (3) The field degradation experiment verified the reliability of the indoor decomposition experiment results. The compound white rot fungi and Sporotrichum thermophile decomposed 29.93% cotton straw during a 50 d field experiment in the winter season and have an unsuitable environment condition such as snow and low temperatures. Discussion Straw returning is the most important treatment for agricultural solid wastes treatment. The lignin, cellulose and semicellulose in cotton stalk decomposition is slow under the natural environment, which influences the following crop germination and seedling emergence. The degradation efficient of compound microbial inoculants is higher than single microorganism. However, in this research, the effect of temperature on degradation effect of cotton straw is minimum than N content and water content. Therefore, the right cotton straw treatment in field should be carry out to maintain the agriculture production and sustainable development. Conclusion The results showed that the compound white rot fungi and Sporotrichum thermophile can degrade cotton straw quickly in field condition under 3% N addition and the ratio of material to water at 1/2. The effects of phosphorus on straw degradation is need to be considered in the subsequent experiments, and the amount of phosphorus added to promote the rapid decomposition of cotton straw in the field should determent by actual soil phosphorus content. Recommendation and perspectives This research provides a significant scientific basis for agricultural solid wastes treatment and an effective method for enhance soil quality. It is recommended that compound white rot fungi and Sporotrichum thermophile is an effective method to degrade cotton straw in field condition. Phosphorus fertilization should be considered in the cotton field management.
Keywords: white rot fungi; Sporotrichum thermophile; degradation; cotton straw; agricultural solid wastes