Decomposition Characteristics And Driving Factors Of Organic Materials In Typical Cropland In China

China has abundant organic resources,with an annual output of 820 million tons of straw,of which corn straw and wheat straw account for 49%;the annual output of manure is 3.8 billion tons,of which pig manure and cow manure account for 84%.Black soil,fluvo-aquic soil and red soil are typical soils in the main agricultural regions of China.Due to the high multiple cropping index,the unreasonable management of farming leads to serious problems of the decline of the soil fertility.Returning organic materials to fields is an important source of soil organic carbon in farmland,which is of great significance for the cultivation and improvement of farmland soil.To explore the decomposition characteristics of organic materials and its driving factors in typical farmland soil,and the effects of returning organic materials on soil nutrients.Nylon mesh bag decomposing test of organic materials in black soil,fluvoaquic soil and red soil were setted.The results are as follows:1.The decomposition rate of straw in all three soils are faster than manure.For the same material,the decomposition rate is the fastest in red soil and the slowest in black soil.The humification coefficient of straw is 11~43%,which varies greatly among different regions.The humification coefficient of manure is 38~57%.Compared with material decomposing alone,soil mixed with material increased the humification coefficient of straw in red soil and reduced the humification coefficient of manure.The twopool equation with soil accumulated temperature can better fit the decomposing process of organic materials in black soil,fluvo-aquic soil and red soil.The equation divided organic materials into labile carbon pool and recalcitrant carbon pool.The classification of each carbon pool component is the comprehensive index of the properties of organic materials and regional environmental factors,for the same material,its stable components decrease from north to south.2.The soil properties are the main driving factors in the process of organic materials decomposition in soil.After removal the effect of soil properties,the material properties are the main driving factors in the process of organic materials decomposing alone.Longer the decomposing time is,the relative contribution of the materials properties will be greater.Straw and manure were analyzed separately in the process of the mixed soil decomposition.The results showed that the main driving factors of straw in the first year of decomposing were the interaction of time,climate factors and soil properties(relative contribution rate is 53.7%).In the process of 4 years’ decomposition,the main driving factor is soil properties(relative contribution rate is 45.3%).During the decomposing process of manure,the main driving factors were time and the interaction of climate and soil in 1 year or 4 years.and the relative contribution rates were 65.5% and 64.8%,respectively.3.The input of straw carbon by returning maize straw stimulates activity of soil organisms,which can convert the soil mineral nitrogen into microbial biomass nitrogen,and further effectively reduce the runoff and leaching of soil nitrogen,improve th soil nitrogen holding capacity.Returning maize straw to the field with nitrogen fertilizer had no significant effect on the rate of decomposition.In the decomposition process of maize straw with nitrogen fertilizer,the main driving factor is the interaction between climatic factors and soil properties,and the relative interpretation rate is 56.7%.4.Straw returning significantly increased the content of amino sugars in the three soils,the increase of glucosamine is the biggest.Although fungi can adapt to a higher carbon-nitrogen ratio environment,the application of nitrogen fertilizer in the soil after maize straw returning to the field still utilizes the accumulation of glucosamine in the soil.The application of nitrogen fertilizer enhances the fungal synthesis ability.Muramic acid is more sensitive to the supply of carbon and nitrogen in the soil.Muramic acid increased rapidly after the return of organic material,but the Muramic acid is easily decomposed and utilizedinto soil to participate the process of carbon and nitrogen cycles.It’s an active component of the organic carbon cycle in soil.In summary,the rate of straw decomposing was faster than manure,and the rate of decomposing of the same material increased from north to south.Nitrogen application did not change the rate of maize straw decomposition,but it could increase the bioavailability of nitrogen in soil.The residual rate of decomposition can be predicted by the accumulated temperature of the soil,the main driving factor for long-term decomposition of straw are soil properties,but the long-term decomposition of manure requires the interaction of time,climate factors and soil properties.