Effects Of Straw Enrichment And Deep Incorporation And Different Crushing Degree Returning To Field On Humus Of Black Soil

"Straw enrichment and deep incorporation"is a new method of returning straw to the field,which increases the content of SOM and humic substances,and improves the structure of humic acid.Previous experiments have studied the effect of straw deep incorporation on soil fertility,but the differences among straw enrichment and deep incorporation,straw mulching and straw deep ploughing is not clear.Therefore,we set up four treatments:no straw（CK）,straw mulching（SCR）,straw deep ploughing（MBR）and straw enrichment and deep incorporation（SEDI）.We focued on the effects of straw enrichment and deep incorporation on soil properties and humus changes.In addition,there are few studies on the changes of humus components and humic acid structure after straw enrichment and deep incorporation at different depths of soil profile,especially under the subsurface.Therefore,we selected two treatments,CK（no straw）and SEDI（returning straw to the field at one time）.To research the effects of straw enrichment and deep incorporation in the soil profile of 0-80cm on the composition of soil humus and the structure of humic acid,the straw was buried in the subsurface layer of black soil（20-40cm）,and the intensity of the staw returning was 15385kg·hm^-2.In addition,few studies discussed about the effect of returning straws with different crushing degrees on soil fertility.So,in order to find the effects of different crushing degree of straw on soil humus components and humic acid structure characteristics,we designed four treatments including no straw（CK）,fine crushed straw（S）,medium crushed straw（M）and coarse crushed straw（L）under the mode of straw enrichment and deep incorporation.The results showed that:（1）There were no significant changes in soil p H and electrical conductivity after straw enrichment and deep incorporation.Straw return was conducive to the accumulation of soil alkali hydrolyzable nitrogen,available phosphorus and available potassium,straw mulching significantly increased the nutrient content of surface soil,and straw enrichment and deep incorporation had more significant effect on the nutrient accumulation of subsurface soil.Straw return with different crushing degrees increased the soil nutrient content,the soil nutrient content was higher when the fine crushed straw was returned to the field.（2）Straw return increased the soil organic matter,the carbon content of each component of humus and the PQ value.Compared with straw deep ploughing and straw mulching,straw enrichment and deep incorporation treatment was more conducive to improve the humus composition of subsurface soil and deepen the humification degree of subsurface soil.Among them,the content of organic matter and humus component C at the depth of 20～30 cm increased the most.SOM and the carbon content of HA,FA and HM increased by 11.59%,38.89%,13.37%and 33.40%respectively compared with CK.As the depth of the profile increases,SOM and the carbon content of HA,FA and HM shows a downward trend.Straw return with different pulverization degrees to the field is beneficial to increase the soil organic carbon and humus carbon content.The SOM and humus carbon content is higher when the fine crushed straws are returned to the field,the soil organic matter content and the carbon content of HA,FA and HM increases by 17.38%,29.29%,17.89%and 15.73%,respectively.（3）Straw return not only reduced the condensation degree,oxidation degree and thermal stability of HA molecular structure,but also increased the aliphatic chain hydrocarbon carbon content and aromatic carbon content,which enhanced the hydrophobicity of the HA structure.The effect of HA structure is much better in SEDI group,compared with straw deep ploughing and straw mulching.And the improvement effect on subsurface soil structure in SEDI group was best,with a maximum effect at the depth of 20-30 cm.As the depth increasing,the effect of straw returning on HA weakened gradually.Returning the crushed straw decreased the condensation degree and oxidation degree of HA,increased the aliphatic carbon content of HA.Fine crushed straw changed the structure of HA more significantly（4）Straw return promoted the growth of crops and the increased of maize yield.The trend of improvement effect was S>M>L>CK.The S,M and L treatments increased corn yield by43.09%,30.39%and 19.89%respectively.And fine straw returning treatment was the best for the growth of crops and the increase of maize yield.