Degradation Limiting Factors Of Straw Deep Tipping And Its Solutions

Crop straw is the main by-product in agricultural production.With the continuous improvement of crop yield,the total amount of crop straw is also increasing.China,the world’s largest food producer,produces more than 900 million tonnes of straw a year.Straw degradation is one of the most direct and convenient ways to promote the reuse of biomass resources.Straw deep tillage can not only improve the soil structure,but also do not affect the germination of crop seeds and provide nutrients for crop growth.However,the decomposition of straw in different depths of soil in Northwest China and the factors limiting straw degradation in deep soil are still unclear.Therefore,the degradation characteristics of straw deep tillage need to be further studied.In this study,the degradation characteristics of straw in different soil layers were explored by using the stratified straw returning experiment in the field,and the main factors affecting straw degradation in different soil depths were revealed.The differences in microbial communities in different soil layers caused by straw returning and their effects on straw degradation were explored.Several anaerobic cellulose degrading strains were isolated and screened.The cellulose degradation effects of strains under single culture and co-culture conditions were evaluated.The results are as follows:(1)Straw returning depth had a significant effect on straw degradation,straw weight loss rate decreased with the deepening of soil layer.In the degradation process,the upper soil moisture content is greatly affected by climate,and the middle and lower soil moisture content is relatively stable.The temperature first decreased and then increased with the increase of soil layer;the oxygen content gradually decreased with the deepening of soil layer.Soil temperature is the main factor affecting straw degradation.(2)The analysis of microbial communities in different soil depths showed that the differentiation rate of soil microbial communities in different depths of non-returning treatment was slow,and the differentiation rate of soil microbial communities in different depths of returning treatment and straw surface soil increased in turn.Through the correlation analysis between environmental factors and soil microbial communities,it was found that the main reason for the difference of soil microbial communities was the difference of soil oxygen content.Further analysis found that deep straw returning increased the number of key nodes of anaerobic bacteria,and anaerobic cellulose degrading bacteria played an important role in the straw degradation process of deep soil.(3)27 anaerobic cellulose-degrading strains were isolated from straw-degrading soil,which belonged to Clostridium.The ratios of transparent circle diameter(D)to colony diameter(d)of 27 strains were greater than 2,and the D/d values of most strains(63%)were between 5 and 10.About 81% of the strains had cellulase activity greater than 5 U/ml,and 41%had cellulase activity greater than 20 U/ml.Compared with the single strain,the enzyme activity of the strain combination culture decreased,and there may be inhibition between the strains.In this study,the degradation of straw in different soil layers was analyzed.It was found that the weight loss rate of straw in shallow soil was the highest,and the microorganisms involved in straw degradation in different depths of soil may be different.Anaerobic cellulose decomposing bacteria may play an important role in the decomposition of straw in deep soil.Isolation and screening of anaerobic cellulose decomposing strains can provide support for deep straw returning technology.