Distribution Of Water Heat And Nutrients During Freezing And Thawing Of Black Soil Slope Farmland Experiment And Analysis

This paper takes the protection of medium-deep seasonal frozen soil area,black soil area,national commodity grain base and ecologically fragile area as the background.Through the field monitoring of natural freezing and thawing process of black soil slope in Northeast China,soil sample selection and indoor soil sample test analysis Etc.,obtain research data and conduct related research.Firstly,the non-structural decision-making variable fuzzy optimization method is applied to optimize the factors affecting the distribution of soil water and nutrient nitrogen and phosphorus during the natural freezing and thawing of black soil slopes,and the key influencing factors are systematically analyzed.Then,with the soil-water-heat and soil-heat-water-salt as the main lines,the soil water heat and nutrient nitrogen and phosphorus distribution during the natural freezing and thawing of the black soil slope in Northeast China were studied.By combining system analysis with simulation verification methods,the following main results are achieved:(1)To carry out the process of analyzing the black slope farmland natural freezing and thawing.The freeze-thaw process of the shady slope and the sunny slope of black soil slope farmland was systematically analyzed,and the development process(time and space characteristics)of the black soil slope farmland during the season was revealed.The thawed soil layer gradually develops to depth,and the soil temperature is getting smaller and smaller during the process of thawing to deeper development,and the thawing time to the depth direction is decreasing.According to the temperature and temperature changes,the freeze-thaw process is proposed.The natural freeze-thaw cycles from late autumn to winter and early spring are divided into six periods according to temperature:pre-freezing,during freezing,early thawing,middle thawing,late thawing,and post-thawing.And define six freeze-thaw periods as a function of temperature and time,F-Tn=f(?,t)=f(?a,?s,t),where n=1,2,3,4,5,6.(2)The distribution of water and heat time in the freezing and thawing process of black soil slope farmland was analyzed.The distribution and verification of soil moisture content in natural frozen-thawed soils including black soil slope farmland.According to the micro-geomorphic black soil slope farmland,the soil moisture content and soil temperature data of the black soil layer in the freeze-thaw process were measured,and the linear,exponential and Gauss simulations of soil moisture content and soil temperature in the black soil layer were systematically analyzed and found in the process of freezing and thawing.The soil moisture content and soil temperature change are closer to the Gauss distribution.The systematic analysis indicated that the soil moisture content of the black soil layer with the time change of the freeze-thaw process accorded with the Gauss distribution.The soil moisture data were verified by periodic micro-geomorphic sloping land monitoring and regular,fixed-point and stratified sampling of wild slope farmland.The verification result is that the soil moisture content of black soil slope farmland is the same as pre-freezing period,freezing period,early thawing period,middle thawing period,late thawing period,and post-thawing period,it has a Gauss distribution,and the maximum soil moisture content in the surface layer appears in the early thawing period.This is consistent with the natural phenomenon of thawing in the early spring of the black soil area.That is,under the conditions of rising temperature in early spring,melting snow,thawing of soil surface and freezing of soil bottom layer,the surface soil water content in seasonal frozen soil area will reach a peak;with the extension of thawing period,the thawing layer will develop to depth,and the soil surface water content will be from saturation to an unsaturated state.During the freezing and thawing process,the soil moisture content of the black soil slope farmland gradually increased from the top to the bottom of the slope.(3)The distribution characteristics of soil nutrient nitrogen and phosphorus in the black-slope sloping field were analyzed.The nutrient contents in the black soil slope sloping land along the slope and the slope direction time and space distribution were studied.The analysis found that:1)in pre-freezing period,that is,after the autumn harvest,the soil nutrient salt is basically evenly distributed on the slope of the slope farmland;2)post-thawing,the soil nutrient salt increases toward the surface;3)During the freezing and thawing process,the nutrient salt of the black soil slope farmland is mainly concentrated in 0-20 cm,the nutrients changed significantly from 0 to 10 cm.From the top of the slope to the bottom of the slope,the nutrient content increased by 40%?276%at the depth of 0-10 cm post-thawing.4)During early thawing period,the nutrient salt of the black soil slope was 0-1 cm increased significantly than pre-freezing,up to 1-2 times;during middle thawing period,the nutrient salt of 1?5 cm increased significantly than pre-freezing,up to 1?2 times;at the late thawing period,the nutrient salt of 1?5 cm increased significantly increase is about 40%than pre-freezing;and post-thawing period,the nutrient salt content of 5?10 cm gradually increases from the top of the slope to the bottom of the slope.According to the research results,it is proposed to control the fertilization of black soil slope farmland,normal fertilization on the top of the slope,and reduction of fertilization at the bottom of the slope to ensure that crop yield can reduce the risk of non-point source pollution in agriculture.The research results of this paper provide technical support for the effective utilization of soil water resources in the northeast black soil slope farmland in the seasonal frozen soil region,and provide useful reference for water resources protection and regional water environment restoration in the construction of commodity grain bases in Northeast China.