Effect Of Temperature And Moisture On Soil Bulk Density And Its Application

Shanxi lacks water and rain,and agricultural production is a typical dry rain-fed agriculture.The development of organic dry farming is an inevitable choice for agricultural development in Shanxi.In recent years,due to the improvement of the level of agricultural mechanization and the popularization of the use of various agricultural operation machinery,the impact on the cultivated land has become greater and greater.The main manifestation is that the machinery has repeatedly pressed the cultivated land,which has increased the compactness of the soil and made the soil more compact.The bulk density of the soil is getting bigger and bigger,and a layer of plow layer of about 10-20 cm is gradually formed in the soil tillage layer.On the one hand,the existence of the plow bottom layer affects the depth of the root system,on the other hand,it prevents the full infiltration of natural rainfall and affects normal agricultural production.In particular,it is an insurmountable bottleneck for the development of organic dry farming in Shanxi.Breaking the plow bottom is the most effective way to reduce soil compaction and soil bulk density.Commonly used aspects are mainly mechanical deep turning,biological interleaving method,and soil "erosion and fragmentation" method caused by soil freezing and thawing in natural ecological environment.The mechanical deep turning can significantly solve the problem of the bottom of the plough,but the mechanical deep turning will roll the soil a second time;the biological aspect is relatively slow;the "erosion fragmentation" method is generally considered to be more of a destructive result caused by soil erosion caused by the environment.However,if the mechanism is studied,the characteristics of the broken soil structure can be used to reduce the bulk density.Soil erosion is a natural phenomenon.In addition to the damage most scholars understand,it can also reduce soil compactness to a certain extent,reduce soil bulk density and ease the process of plow bottom formation.The effect of freeze-thaw alternation on soil bulk density It is because the volume of water in the soil changes from a liquid form to a solid form under the freeze-thaw cycle,which increases the pores in the soil and reduces the bulk density.For cultivated soils,the decrease in soil bulk density will have a positive impact on agricultural production.The looser and more air-permeable surface soil provides a better environment for the growth and extension of crop roots and space to absorb nutrients and water.At present,the cognition of the effects of freezing and thawing on soil under natural conditions is more qualitative,and it is believed that freezing and thawing will reduce soil bulk density.However,there are relatively few studies on the quantitative influence of freezing and thawing process on soil bulk density under specific temperature and soil moisture content.To this end,this study took the typical cinnamon soil in Shanxi Province as the research object,and set different initial bulk density,temperature,moisture,and freeze-thaw times in the room to determine the change in soil bulk density during the freeze-thaw process,and quantitatively analyze the effect of freeze-thaw on bulk density.Impact.This paper collects surface soils of various typical farming soil types in Shanxi Province and conducts fixed-point sampling and analysis in Taigu District,Jinzhong City,Shanxi Province,in order to pass the provincial soil survey and adopt the Kriging interpolation of the Arc GIS Central Geostatistics module.The method simulates the distribution of soil bulk density across the province.Through the experimental analysis of the soil sampled at fixed points,the influence of freeze-thaw alternation on soil bulk density is obtained,and the regression statistics method is used to establish the change of soil bulk density determined by soil environmental factors and its own attribute factors during freeze-thaw alternation.Multivariate linear prediction model.Obtain the measured data through the monitoring of the weather station,combined with the remote sensing inversion technology,use the MODIS data to remotely predict the soil water content and surface temperature in Shanxi Province,and combine the model with the province’s bulk density distribution to obtain the province’s soil bulk density under the condition of alternate freezing and thawing The change situation.Research indicates:1 Under the conditions of different soil water content,the change range of soil bulk density under the influence of freeze-thaw alternation increases with the increase of soil water content.Under the conditions of fixed temperature difference and initial bulk density,under the 4 water content conditions of 10%,15%,20%,and 25%,the variation range of soil bulk density fluctuates between 0.5% and 2.8%.The reason for the fluctuation is different water content and water content.The initial bulk density affects the change range of temperature on the soil bulk density under the action of freeze-thaw alternation;under different water content conditions,the volume of water condensed into crystals in the soil with higher water content is less.2 Under the conditions of different soil temperature differences,the variation range of soil bulk density under the influence of freeze-thaw alternation increases with the increase of temperature difference.Under the conditions of fixed soil moisture content and initial bulk density,under the four water content conditions of-5℃~5℃,-10℃~10℃,and-20℃~10℃,the variation range of soil bulk density varies from 0.1% to 2.5%The reason for the floating is that different temperature differences and initial bulk density affect the change range of soil moisture content to soil bulk density under the alternating effects of freezing and thawing;under different temperature differences,the degree of moisture condensation in the soil is different.3 Under the condition of different initial bulk density,the change range of soil bulk density under the influence of freeze-thaw alternation decreases with the increase of initial bulk density.Under the conditions of fixed temperature and soil water content,under the four water content conditions of 1.3,1.4,and 1.5,the variation range of soil bulk density fluctuates between 0.8% and 1.2%.The reason for the fluctuation is that different temperature differences and initial bulk density affect the soil content.The amount of water affects the variation of soil bulk density under the effects of alternate freezing and thawing.The soil with higher initial bulk density has less soil pores,and the kinetic energy required for water condensation is greater,so it is more difficult to expand soil pores.4 The change of soil bulk density established during freeze-thaw alternation.The coefficient of determination of the multiple regression linear prediction model is 0.92,and the F value is 863.1,which passes the F test;all parameters pass the T test,and the relative error average of the modeling sample It is1.81%,the average relative error of the verification sample is 1.25%,and the accuracy of the two is equivalent,both between 1% and 2%.The relative error averages of the modeling sample and the verification sample are both low,indicating that the model has a certain verification accuracy.The coefficient of determination between the predicted value and the measured value is 0.96,which indicates that the change trend of the predicted value and the measured value is basically the same.5 The model shows that as the number of freeze-thaw cycles increases,the soil bulk density will gradually decrease to a certain range and then stabilize and no longer change.The change in bulk density is determined by the soil moisture content,freezing temperature and dissolution temperature.Among the factors that affect the change of bulk density under freeze-thaw alternation,soil water content has the greatest impact on it,with an influencing factor of 0.086,followed by freezing temperature,which is 0.007,and dissolution temperature,which has the least effect,only 0.001.6 Remote sensing inversion of land surface temperature uses the surface temperature product in the modis data for inversion.The temperature difference between north and south in Shanxi Province is large,and the freeze-thaw cycle mainly occurs in the central and northwestern parts of Shanxi.The influence of freezing and thawing on soil bulk density is the most obvious in northern Shanxi.7 The remote sensing inversion of soil water content adopts the thermal inertia method.After radiometric calibration of the modis image data,the inversion obtains the surface temperature difference and total reflectance values.The thermal inertia model can be used to obtain the soil thermal inertia distribution in Shanxi Province.Combined with the relationship between the sampling time and the coordinates of the sampling point and the modis image,the inversion value of the soil thermal inertia method during sampling at each sampling point is obtained,and the functional relationship between the inversion value of the soil thermal inertia and the measured soil moisture content is established,and the unity is obtained.Linear regression model,and R2 reached 0.65,indicating that the model can explain the relationship between soil moisture content and soil thermal inertia retrieved by remote sensing to a certain extent.The soil thermal inertia was corrected by this model,and the distribution map of soil water content in Shanxi Province was obtained.8 When the Kriging method is used to simulate the soil distribution in Shanxi Province,the soil bulk density data is simulated using 42 points sampled in the whole province.The simulation results show that the soil bulk density in the central part of Shanxi Province is low,and the bulk density level is generally between1.293 and 1.336,while the soil bulk density in the north and south of Shanxi Province is relatively high,and the soil bulk density in the southern part of Shanxi Province is between 1.419 and 1.481.The soil bulk density in northern Shanxi Province is between 1.419 and 1.481.9 When the simulated Shanxi province bulk density change was tested and verified,the trend was basically the same,and the measured value was much lower than the simulated value.The measured value of soil bulk density changes by about 10% after five freeze-thaw cycles,while the predicted value of soil bulk density changes by 19% under the influence of alternate freeze-thaw cycles.The reason is that the initial bulk density is quite different,and the difference in initial bulk density is because when the ordinary kriging interpolation method is used to simulate the soil bulk density in the province,due to the problem of fewer measured points,the simulated numerical value is higher in some areas.