Effects Of Different Modification Measures On Shrinkage Property Of Typical Shajiang Black Soil And Wheat Physiology

Shajiang black soil is a recessive soil formed by long-term dry-wet alternating process under the leading role of parent material and topography.It is widely distributed in the Huang-Huai-Hai Plain,The distribution area of Huaibei Plain is the largest.Due to the high clay content of this type of soil(>35%)and the clay mineral montmorillonite of 2:1 type,it is easy to swell and shrink,and the soil ploughing ability and water retention capacity are poor,which seriously affects the growth of crops,is a typical medium and low yield soil in China.In addition to the need to strengthen water management for the reduction of the barrier factors of Shajiang black soil,it is also possible to apply modified materials such as fly ash,bio-carbon,and straw returning in the field.Different modification measures can significantly improve the basic physical and chemical properties of soil and improve soil fertility,but there are few studies on soil swelling and shrinkage,and the relevant mechanisms are not clear.This study relies on field experiments and pot experiments to study the occurrence and influencing factors of physical barrier factors in Shajiang black soil.The physicochemical characteristics of typical Shajiang black soil under different modifiers and their effects on the growth of typical crop wheat were studied.The main results obtained are as follows:(1)Soil improvement long-term positioning test(2016?2018)results show:Fly ash,biochar and straw returning to the soil can increase soil nutrient content and field water holding capacity to a certain extent,and reduce soil bulk density,which is most obvious when treated with straw returning.The addition of fly ash and biochar reduced the linear expansion coefficient(COLE)of the soil,while the addition of straw increased the linear expansion coefficient(COLE)of the soil.(2)According to the long-term positioning test(2007-2017),the results of different straw returning fields showed that WMS+F2<WS+F2?MS+F2?F2<CK2 was the soil bulk density,which was opposite to the change of soil field moisture capacity(FC);The field moisture capacity of WMS+F2 treatment is 38%,which is 7.38%higher than CK2.And the difference values of soil specific volume significantly(V")have positive relations with the coefficient linear extensibility(COLE)and the soil organic matter(SOM).Although the accumulation of SOM reinforces soil shrinkage property,the mechanism on increasing soil water and nutrition capacity can achieve the reduction of soil shrinkage-prone property.What's more,the WS+F2 treatment can remarkably improve the content of SOM,while MS+F2 treatment has large effects on soil macroporosity because of difficult degradation of maize straw.Hence,wheat-maize double cropping straw returning(WMS+F2)is more suitable for the improvement of soil structure and practical production demand.(3)Pot experiment results show:although the addition of fly ash and straw carbon can significantly increase soil water holding capacity,it has poor water retention performance compared with straw returning.On the 8th day of drought stress,the addition of straw treatment was the best,and the accumulation of various enzymes in the osmotic adjustment substance proline(Pro)and antioxidant enzyme system was higher than other treatments;Straw carbon treatment has higher soil water content,but the combination of various enzymes in the antioxidant enzyme system is poor,showing peroxidase(POD),ascorbate peroxidase(APX)and glutathione reductase(GR)low content;The soil moisture of fly ash treatment decreased rapidly and the combination of antioxidant enzyme system was poor,which caused serious damage to crop membrane(MDA)and accumulated more hydrogen peroxide(H2O2).