Effects Of Freeze-thaw Cycles And Initial Soil Water Content On Soil Disintegration Rate In Chinese Mollisol Region

The Heilongjiang province is the main Mollisol distribution area in China.However,the thickness of Mollisol layer in this region has been declining due to intense agriculture activity,water erosion,wind erosion and freeze-thaw function.The soil disintegration rate is an important index to characterize soil erodibility.During the past decades,studies on soil disintegration have been concentrated on the Loess Plateau,but there is less reports regarding freeze-thaw cycle impacts on the soil disintegration,especially researches on soil disintegration in the Chinese Mollisol region where freeze-thaw cycle occurs frequently within a year is still lacking.Thus,this study collects tested soils from Binxian and Keshan counties in Heilongjiang province,China to measure soil disintegration.The improved indoor soil disintegration experiment method was used to evaluate the effects of freeze-thaw cycles with different initial soil water contents on soil disintegration rate in Chinese Mollisol region.The treatments covers five different times of freeze-thaw cycles(0,1,3,5,and 7),three initial soil water contents(16.5%,24.8% and 33%),and two tested soil with remolded and undisturbed soil samples.The specific aim of this study quantifies how freeze-thaw cycle and initial soil water content influence on soil disintegration rate in Chinese mollisol region.The results can reveal mechanisms of freeze-thaw effects on soil erodibility and to enhance the understanding of water erosion process and mechanism in this multi-agent erosion area.The main results are as follows:(1)The Mollisol disintegration rate decreases by 3 times when the initial soil water content increases from 16.5% to 24.8% and soil samples are disintegrated completely within 6 minutes and soil disintegration duration at 16.5% initial soil water content is 5 times shorter than that soil samples at 24.8% and 33.0% initial soil water contents.(2)The KS soil disintegration rate increases sharply by 3 times when soil experiences one freeze-thaw cycle;when freeze-thaw cycle increases from 5 to 7 times,the soil disintegration rate increases by 2 times;while BX soil disintegration rate increases gradually with an increase of freeze-thaw cycles.The disintegration duration of KS soil is shortened by 64% when soil experiences one freeze-thaw cycle;and then it decreased 95% after seven freeze-thaw cycles;while the duration of the BX soil disintegration process increases gradually with increase of freeze-thaw cycles.Moreover,the KS soil disintegration rate is 5 times higher than the BX soil disintegration rate when the freeze-thaw cycles increase from 3 to 7 times.Therefore,the KS soil disintegration duration is 10 times shorter than that for the BX soil when the freeze-thaw cycle increases from 0 to 7 times.(3)The KS soil disintegration rate for undisturbed and remolded soil samples increases five and six times,respectively,when the freeze-thaw cycle increases from 3 to 7;while BX soil disintegration rates for remolded and undisturbed soil samples increase gradually with increases of the freeze-thaw cycles.(4)The correlation coefficients between the soil disintegration rate for both BX and KS tested soils and the number of freeze-thaw cycles were 0.906 and 0.906,respectively,which is showed that soil disintegration rate has positively correlated with freeze-thaw cycles(P <0.05);while soil disintegration rate for both tested soils has negative correction with the initial soil water content and the correlation coefficients are-0.764 and-0.858,respectively.