Comparative Study On Effect Of Freeze-Thaw On Aggregate Water-Stability Of Black Soil And Brown Soil

Soil particle structure, one necessary soil condition of crop high production, canprovide plants with nutrients through mineralization, making sense of formation andstability of soil structure. Soil aggregate is important soil component, possessing threeeffects in soil that is coordinating and ensuring water, fertilizer, gas and heat in soils,affecting variety and activity of soil enzyme, and maintaining and stabilizing soilanthropic epipedon. Soil aggregate has important role in soil physico-chemicalproperties, improvement of quality and function in soil, and plant growth. The existedresults showed that freeze-thaw effect is key factor affecting soil aggregatewater-stability. There were little studies about the law of effect of freeze-thaw eventon soil aggregate stability, and different kinds of soil has different variety of soilaggregate stability because of difference in soil physio-chemical properties andstructure characteristics. Taking black soil and brown soil, typical cropland inNortheast China, as test object, variation of effect of freeze-thaw event on aggregatewater-stability of black soil and brown soil was studied by indoor simulationfreeze-thaw experiment on the base of former studies. The results showed that:1. Initial moisture content is key factor affecting soil aggregate water-stability.The critical moisture content of black soil is40%. Water-stable aggregate willachieve peak value when initial moisture content is40%for aggregate in particle sizemore than1mm. Water-stable aggregate in particle size more than1mm will decreasewhile aggregate in particle size1～0.5mm and0.5～0.25mm will increase wheninitial moisture content is more than or less than40%.Water-stable aggregate (＞5mm,5～3mm,3～2mm), which critical moisturecontent is25%, will firstly increase and latterly decrease with boost of initial moisturecontent, and water-stable aggregate (2～1mm,1～0.5mm) will firstly increase andlatterly decrease whose peak value show up when initial moisture content is between20%and25%. Water-stable aggregate (0.5～0.25mm) will steadily decrease withtendency to gentle.2. Freeze-thaw cycles are important factor affecting soil aggregate water-stability.Water-stable aggregate (＞5mm,5～3mm,3～2mm,2～1mm) will graduallydecrease while water-stable aggregate (1～0.5mm,0.5～0.25mm) will graduallyincrease for black soil with increase of freeze-thaw cycles.Water-stable aggregate (＞5mm,5～3mm,3～2mm) will slowly decrease orchange gently while water-stable aggregate (2～1mm,1～0.5mm,0.5～0.25mm) willslowly increase or change gently for brown soil with increase of freeze-thaw cycles.3. Freezing temperature is important factor affecting soil aggregatewater-stability.Water-stable aggregate (＞5mm,5～3mm) will decrease while water-stableaggregate (1～0.5mm,0.5～0.25mm) will increase for black soil with decrease of freezing temperature. Not significant influence was studied for water-stable aggregate(3～2mm,2～1mm).Water-stable aggregate (＞5mm) will reduce while water-stable aggregate (5～3mm,3～2mm,2～1mm) will firstly decrease and latterly increase for brown soil withdecrease of freezing temperature. Water-stable aggregate (1～0.5mm,0.5～0.25mm)will gradually increase with tendency to gentle.4. In comparation to brown soil, effect of moisture content、freeze-thaw cycles、freezing temperature on aggregate water-stability is more obvious.