An Experimental Study On The Effect Of Snow Surface Cover On The Mechanism Of Soil Water,heat And Salt In Shihezi Irrigation Area

Seasonal soil freezing and thawing in Shihezi Irrigation District,causes annual changes in soil water,heat and salt,which in turn influences the soil environment needed for crop growth.Meanwhile,the abundant snowmelt resources play an important role in arid and semi-arid Shihezi irrigation regions.The study explored the spatial-temporal distribution and migration among water,heat and salt in soil,as well as the mechanism of changes between the three,under the combined snow cover and surface cover during seasonal freezing and thawing,and provided reference for assessing the environment of soil water,heat and salt in the coming spring in Shihezi Irrigation District.In this paper,three kinds of straw,plastic film,activated carbon and bare ground control were set up,and the field plot test was conducted for 2 consecutive years(November 29,2015—April 5,2016 as the first trial period,November 13,2016—April 10,2017 as the second trial period).Field experiments and laboratory analysis were used to conduct a pilot study to comprehensively and systematically reveal the regulatory mechanisms of different land cover types on soil water,heat and salt migration during freezing-thawing period.The main findings and conclusions are as follows:(1)During the soil cooling stage,the maximum and minimum temperature difference in the 10 cm soil layer is the most dramatic,and the corresponding maximum temperature ranges are bare(6.14°C and 3.78°C)> mulching(5.58°C and 3.70°C)> straw mulching(5.17°C and 3.53°C)> activated carbon coverage(4.98°C and 3.41°C)(Note: The former is the first test period data,the latter is the second test period data,the same below).With the increase of soil depth,the soil temperature gradually weakens,but overall there is a consistent law of changes.During the warming phase,the frozen soil layer in the bare ground begins to ablate first,then the coverage of straw,activated carbon,and plastic film lag behind bare ground by 12 days and 10 days,4 days and 2 days,2 days and 1 days,respectively.The effect of stagnation temperature is straw mulching> activated carbon mulching> mulching,and the temperature of stagnation is not conducive to the ablation of permafrost.It can be seen that surface cover only affects the exchange frequency of heat movement between the earth and gas,which plays a role in regulating soil temperature changes and does not fundamentally change the soil temperature changes.(2)At the initial stage of freezing,the moisture content in the 0—10cm soil layer covered by mulch,activated carbon and straw,etc.increases by 3.92% and 3.43%,1.32% and 1.99%,0.53% and 1.76%,4.20% and 5.49%,respectively,compared with the initial moisture content in the two test periods.The increase in salt content mainly occurs in the 0—20 cm soil layer,correspondingly increases 5.71%,6.18%,3.63%,7.27%.During the period of stable freezing,the water and salt in the 10—20cm soil layer increases significantly,especially in the areas of mulch and activated carbon.During the melting period,the increase of soil water content in 0—30cm soil layer is the highest(9.18% and 9.24%)covered with activated carbon,followed by straw mulching(7.01% and 6.74%)> bare land(6.50% and 4.61%).The soil with the greatest increase in salinity is,respectively,bare soil in 30 cm(20.75%),plastic film cover in 20 cm(10.96%),straw cover in 0 cm(13.33%)and activated carbon cover in 0 cm(9.40%).After the whole process of seasonal freezing and thawing,the coverage of straw,activated carbon,etc.shows a significant effect of preservation and inhibition of salt.The effects of soil moisture conservation and salt suppression on bare land and plastic film are both relatively poor,due to the infiltration of snow melt water and the strong evaporation on the bare land surface.(3)The response relationships between soil water content,salt content and soil temperature,soil depth are established.The coefficient of determination is above 0.747,reflecting the close interaction between soil hydrothermal salt and soil layers at different depths.(4)Before and after the experiment period,in 0—10cm soil layer,in terms of the increasing of soil water storage,the results are: activated carbon coverage(15.52 and 13.89 mm)> straw coverage(6.03 and 5.54 mm)> bare land(5.42 and 0.98 mm)> plastic mulching(5.15 and 4.85 mm),the increase in soil water storage under activated carbon coverage is 29.87% and 31.24%,33.98%,and 33.93%,32.51%,and 48.09% higher than that of straw mulching,bare land,and plastic film coverage,respectively,reflecting good conservation effects and higher utilization of snowmelt water.In terms of the increase in salt storage per unit area,the results are: bare land(2.78 and 2.80g)> plastic mulching(2.36 and 2.88g)> straw mulching(2.03 and 2.79g)> activated carbon coverage(2.27 and 2.66g),and the change rate of soil salinity in bare land is the highest(27.92% and 25.78%),which are 17.84% and 13.45%,10.18% and 10.14%,3.32% and 3.91% more than those covered with activated carbon,straw,and plastic film,respectively.The contrast can show that the surface cover has significant salt inhibition effects.