Variation Characteristics Of Cold Season Surface Soil Moisture In Northeast Black Soil Region

our country as world’s third frozen soil country,seasonal frozen soil area accounted for more than half of the country’s land area.Black soil region of Northeast distribute in Heilongjiang, Jilin, Liaoning and Inner Mongolia,which located in seasonal frozen soil area,soil freezing and thawing process continues over half years annually.Existing research shows,seasonal frozen soil area’s surface soil have several times’s freezing and thawing action in all winter, in snow melting period,freezing and thawing action changes topsoil soil moisture content and soil moisture’solid&liquid state to change topsoil’s mechanical components, bulk density, Shearing resistance, aggregate stability to affect the erosion resistance index.In Snow melting period, generated snow melting runoff causes more serious soil erosion and then increases the possibility of soil erosion.Soil moisture migration during soil freezing refers to soil moisture migrate from the potential energy high to potential energy low, the migration of soil moisture leads to the increasement of soil moisture content in the frozen layer and then affect the soil erosion resistance index. Freeze soil moisture migration theory is extended to the space of topsoil moisture variation in cold season in this study and research on the variation characteristics in different spatial scales of topsoil moisture in cold season, this have great influence on understand the variation of soil erosion resistance in Snow melting period of freezing and thawing action and reveal the corresponding surface runoff production and soil erosion prevention. This paper takes black soil region of Northeast China as research area, research on ridge farmland and nearby woodland in low mountain and hilly area of Black Soil in Northeast China, research on different slope position, different slop aspect and different land use’s topsoil moisture variation characteristics in freezing period through field observation experiment. On the basis of these, make analysis of rainfall, air temperature and other meteorological data, reseach on differences of topsoil moisture in two years, research results show that:(l)In the depth of 0-30cm topsoil, Hailun, Xifeng, Meihekou and Zhalantun sampling slope cultivated land’s soil moisture has the process of migration obviously, soil moisture migration quantity in the early stage is larger. Freezing soil moisture content increases significantly compared with not freezed, the increasement of soil moisture is Brown soil(Xifeng)>Albic soil(Meihekou)>Black soil(I lailun)>Dark brown soil(Zhalantun), respecti vely as 6.4%.4.1%,1.5%,0.6%.0-30cm topsoil soil moisture content is Black soil (31.6%). Dark brown(27.4%), Albic soil(21.7%), Dark brown soil(23.6%). In the vertical direction, 0-10cm layer’s soil moisture migration quantity is larger than other layers in four regions, the difference of topsoil profile distribution leads to the difference of increasement of soil moisture.0-10cm layer’s soil moisture increasement of black soil is the most large, averaging increase 4.3%,0-20cm and 0-30cm layer’s soil moisture increasement is less, averaging increase 0.8% and 0.7%, topsoil soil moisture increasement in Xifeng and Meihekou sampling slope is Homogeneous. Dark brown in 0-10cm.0-20cm and 0-30cm topsoil soil moisture increasement is 4.7% and 2.7% and 3.1%, Albic soil in 0-10cm，0-20cm and 0-30cm topsoil soil moisture increasement is 2.3% and 1.8% and 2.7%. Dark brown soil in 0-10cm, 0-20cm,0-30cm topsoil soil moisture increasement is 1.02% and 0.75% and 0.7%.(2)On the slope scale,the result of soil erosion on the slope changes the thickness of the surface soil, changes of topsoil’s thickness causes changes in soil physical properties to affect the variation of topsoil soil moisture in freezing period. In different regions’s sampling slope,due to the difference of soil, topography and extent of tillage disturbance leads to the differences of soil moisture distribution in freezing period, thereby affect the freezing process in soil moisture to the migration of the surface. The soil moisture migration quantity in different slope positions of Hailun sampling slope cultivated land is mainly affected by the soil physical properties, the soil moisture migration quantity in different slope positions of Xifeng and Meihekou sampling slope cultivated land is mainly affected by the topography. The soil moisture migration quantity in different slope positions of Zhalantun is less affected by the external environment. Hailun sampling slop topsoil soil moisture increasement is downhill position(5.4%)>Uphill position(4.7%)>Middle slope position(1.2%), Xifeng sampling slope topsoil soil moisture increasement is Middle slope position(6.6%)>Uphill position(2.8%)>downhill position(2.1%), Meihekou sampling slope topsoil soil moisture increasement is downhill position(5.4%)>Middle slope position(3.6%)>Uphill position(3.1%). In different slop aspect, due to the differences of solar radiation leads to topsoil soil moisture changes differently. The differences of topsoil moisture to different slope is larger in Hailun and Xifeng’s sampling slope, the differences of topsoil moisture to different slope is smaller in Meihekou and Zhalantun.(3)In different regions’s sampling slope,0-30cm topsoil soil of different land use is different due to the different vegetation cover, root distribution, topography and other factors. In 0-30cm topsoil soil of different land use, the soil physical properties is different. Different soil physical properties will affect the soil moisture holding capacity and moisture conductivity to affect the topsoil moisture in the freezing period. In the samping slope of Hailun, due to forest surface soil’pore connectivity is better than cultivated land leads to the surface migration quantity and range are larger than the cultivated land, the increasement of 0-30cm soil moisture is woodland(5.4%)>cultivated land(0.84%). in the samping slope of Xifeng, the sand content in the topsoil is higher than forest land, soil moisture holding capacity is poor, shallow soil moisture content is small. Therefore, the soil moisture migration is less than cultivated land, the increasement of 0-30cm soil moisture is cultivated land(4.8%)>woodland(3.9%), in the samping slope of Meihekou, the differences of forest surface soil and farmland soil in the profile were smaller, more soil root content of forest land leads to moisture consumption stronger, the shallow soil moisture content in the soil is relatively low before freezing, the soil moisture migration is less than cultivated land, the increasement of 0-30cm soil moisture is cultivated land(4.2%)>woodland(2.4%), in the samping slope of Zhalantun, evaporation intensity of cultivated land surface soil is greater leads to the surface soil drier before freeze due to the vegetation canopy cover. Due to vegetation canopy cover of the forest surface soil, the surface soil is moist before freeze, therefore the soil moisture migration is larger than cultivated land, the increasement of 0-30cm soil moisture is woodland(1.8%)>cultivated land(0.5%).(4)Between the year of 2013-2014 and 2014-2015, climate changes, environmental conditions make frozen topsoil moisture interannual differences. During the two-years period, the differences of Hailun and Zhalantun sampling’s surface soil moisture is small. Xifeng and Meihekou is larger, F-value is 2.07,3.62,12.69 and 24.02, this is mainly affected by rainfall, soil and other factors. Soil water storage performance is better in Hailun’s sampling slope during the two-year period, the effect of rainfall’s difference on soil moisture is smaller. Soil moisture storage performance is a little bit worse in Xifeng sampling slope, the effect of rainfall’s difference on soil moisture is a bit more. Soil moisture storage performance is worse in Meihekou sampling slope, the effect of rainfall’s difference on soil moisture is large. The difference of rainfall leads to the different moisture storage of the shallow soil before freezing and leads to the difference of soil moisture content in freezing period. There are no significant effect on the difference of climatic condition of spatial distribution pattern of topsoil moisture in the freezing period. In two-year freeze period, the mechanism of different soil moisture spatial variability. From the year scale, Hailun sampling slope’s topsoil moisture variation pattern is consistent in a period of two years, effect of slope position, slope aspect and land use on spatial variability of topsoil moisture is significant, effect of slope position, slope aspect and land use on spatial variability of topsoil moisture is small in Zhalantun, effect of slope aspect and land use on spatial variability of topsoil moisture is significant in Xifeng and Meihekou.