Effect Of Biochar On Hydraulic Characteristics And Water Transport Of Hetian Aeolian Sandy Soil

Aeolian sandy soil is one of the main soil types used for agricultural production in Hetian region,Xinjiang.Due to its characteristics of poor physical structure,low organic content and hard to retain moisture and fertilizer,it restricts the expansion of agricultural land and economy development in this region.The biochar can repair and improve soil conditions as a new type of soil amendment,.In order to analyze the impact of biochar to the hydraulic characteristics and moisture imgration properties in aeolian sandy soil,the study designed and set up five different biochar mount to add to the relative sandy soil,in which the mass ratio were 0%(CK),4%(T1),8%(T2),12%(T3),16%(T4),by determining the structure of the soil,soil moisture constant,soil water dynamics parameters and characteristic parameters of soil moisture front and wet soil body moisture content distribution index.This study mainly analyzed the soil hydraulic characteristics when added different quantity of biochar and soil moisture migration rule in different head flow condition.the result revealed the controlling mechanism of biochar on the moisture retaining quality and infiltration characteristic of sandy soil,and determined the optimized amount of biochar in sandy soil.The main conclusions were as follows:(1)The application of biochar in aeolian sandy soil could effectively reduce the bulk density and improve the porosity of aeolian sandy soil.With the increase amount of biochar content,the saturated water content,field water capacity and available water content of each treatment all increased significantly.The soil capillary porosity increased first and then decreased with the increase amount of biochar content,and the maximum soil capillary porosity was found in T3 treatment,which was 5.61%higher than that in CK treatment.Biochar improved the water characteristic curve of soil,the water holding capacity,and specific water capacity.The strongest effective water supply capacity of soil was found in T3 treatment.(2)Under the same flow rate conditions,both horizontally(X direction)and vertically(Z direction)the migration distance and migration rate of moisture front decreased with the increase amount of biochar content,and the wet soil's width to depth ratio increased first and then decreased with the increase amount of biochar content.Under different flow rate conditions,the migration distance of moisture front decreased with the increase of flow rate in horizontally direction,and reacted the opposite in vertically direction in the CK treatment.The width to depth ratio of the wet soil body decreased with the increase of flow rate in the CK treatment.Affected by the infiltration of stagnant water,the migration distance was 3.2 L·h^-1>1.8 L·h^-1>2.5 L·h^-1 in horizontally direction,the migration distance was 2.5 L·h^-1>1.8 L·h^-1>3.2 L·h^-1 in vertically direction,the wet soil body aspect ratio was 1.13,1.08 and 1.37 respectively with the increase of flow rate.(3)At the end of infiltration,with the increase of biochar content,the volume of the wetted body in each treatment decreased,and the average water content of the wetted body increased.At different flow rates,the average water content of the wetted bodies in each treatment was not much different;The increase in flow rate caused the water distribution in the vertically direction to be greater than that in the horizontally direction in the CK treatment,and the T3 treatment was not much different with the water distribution in the two directions under a flow rate of 1.8 L·h^-1 and 2.5 L·h^-1,At a flow rate of 3.2 L·h^-1,the water distribution in the horizontally direction was greater than that in the vertically direction.At 24 hours after the end of infiltration,the wetting front of each treatment spread out evenly,the volume of the wetted body increased,the water content of the wetted body was extremely reduced,and the average water content was lower than compared with that at the end of irrigation.(4)From the perspective of improving water holding capacity in sandy soil,it is recommended that the appropriate amount of biochar content in Hetian sandy soil is 12%(T3 treatment).