Effects Of Aggregates Combination On Soil Hydraulic Properties

Soil is the link between surface water and groundwater,it plays an important role in theformation,transformation and consumption of water resources,and is closely related to agriculture,hydrology and the environment.Soil aggregates are basic units of soil structure.Its shape,size,distribution and composition affect the physical properties of soil,such as water holding capacity,aeration and bulk density,and then affect soil quality.This study focuses on the effects of different soil aggregates on the hydraulic properties of three agricultural typical soils-black soil,red soil and loess.It can provide important theoretical basis for soil irrigation,soil improvement and crop growth.The main results of this study are as follows after laboratory soil pipe experiment and CT scanning technique.（1）The maximum K₁₀ of pure aggregates of black soil,red soil and loess was from 8-2 mm,8-2 mm and 2-0.25 mm aggregates,respectively.Organic matter content and particle size distribution were the main factors affecting the change of soil saturated hydraulic conductivity.When 8-2 mm and 2-0.25 mm aggregates accounted for 60%of the total soil mass,respectively,the K₁₀ of the three mixed soils was higher than that of the undisturbed soil.When<0.25mm aggregates were in the upper layer and 8-2 mm aggregates in the lower layer,the K₁₀ of the black soil was the highest.（2）Evaporation of 2-0.25mm aggregates was strongest in black and red soils.The strongest evaporation of loess was the 8-2 mm aggregates.Evaporation of pure aggregates of the three soils was stronger than that of undisturbed soil in the early stage,especially in loess.Evaporation of loess was greatly affected by the number of macropores and the connectivity of macropores.There was a great effect of mixed treatment on soil evaporation.But it could not be explained by the porosity condition.When<0.25 mm aggregates were in the upper layer,black soil evaporated strongly in stage 2.When 8-2 mm aggregates in upper layer and<0.25mm aggregates in lower layer,black soil evaporation was weak in the whole process.The evaporation of red soil was weak in the early stage when 8-2mm aggregates in the upper layer.And the evaporation of loess was strong in the late stage when 8-2 mm aggregates in the upper layer.（3）The water retention capacity of black soil was strongest.The black soil had the strongest water retention capacity of 2-0.25 mm aggregates,and the weakest was 8-2 mm aggregates.The water retention capacity of mixed black soil with 2-0.25mm aggregates accounting for60%was also the strongest,while the it was the weakest with 8-2mm aggregates accounting for 60%.In layered black soils,the water retention capacity was the strongest when 2-0.25mm aggregates in the lower layer and the weakest when it was in the upper layer.The water retention capacity of<0.25mm aggregates was the strongest,and that of 2-0.25mm aggregates was the weakest.After mixing,the water retention capacity was the highest when the<0.25mm aggregates accounted for 60%,and the weakest when the 2-0.25mm aggregate accounted for60%.For layered treatments,the water retention capacity was highest when<0.25mm aggregates in the upper layer and the 2-0.25mm aggregates in the lower layer.And it was weakest when<0.25 mm aggregates in the lower layer.The water retention capacity of red soils was close no matter how the aggregates are distributed.Its air-entry value was the minimum,and the saturated water content was the highest among three soils.Different combinations of aggregates affect the hydraulic properties of black soil,red soil and loess.The organic matter content and the content of<2mm aggregates play important roles of soil water retention capacity.In the improvement of soils with poor hydraulic properties,necessary aggregates can be added while maintaining porosity to the greatest extent.