Study On Water And Gas Transport Characteristics Of Four Texture Soils

The soil is composed of three phases of solid-liquid gas.The air of the soil exists in the pores of the soil.The water generally occupies a small pore,and the gas occupies a large pore.The transport properties of gases and water in the soil are important determinants of the quality of the soil supporting plant growth.The better the ventilation,the better the growth of the plants,and conversely,reducing the ventilation may reduce the growth of the plants.In addition to the need to breathe air,plants also need water,which is the main metabolic agent for growth and a source of H-cells for photosynthesis.Plant roots absorb water from the soil,and the transport properties of soil moisture become the determinant of plant growth.In order to study the water and gas transmission characteristics of four texture soils,four soils including Lou soil,loess soil,sandy soil and black soil were selected as research objects.The saturated hydraulic conductivity of soil was determined by MPD method,one-dimensional precipitation method and fixed head method.Three-dimensional and one-dimensional measurements of relative gas diffusivity of soil at different water contents.According to the results of different soil box experiments,different methods were used to determine the difference between saturated hydraulic conductivity and relative gas diffusion rate.A new method for rapidly determining the saturated hydraulic conductivity in the field is obtained,which is convenient and quick.The factors affecting the saturated hydraulic conductivity and the relative gas diffusion rate are analyzed.An empirical formula for estimating the saturated hydraulic conductivity by relative gas diffusion rate is proposed.Research indicates:(1)K_s has great uncertainty.Different methods can be applied to different soils to draw different conclusions.The relevant laws are affected by the measurement operation.The saturated hydraulic conductivity measured by the three methods in the four texture soils was MPD method>one-dimensional precipitation head method>fixed water head method.Regression analysis between the three methods,significant correlation between MPD method and one-dimensional precipitation method,R~2=0.91.The variability of saturated hydraulic conductivity of different texture soils is different.Lou soil and loess soil are strong variability,and sandy soil and black soil are moderately variability.The saturated hydraulic conductivity is negatively linearly related to the bulk density,R~2=0.99.There is a linear positive correlation between saturated hydraulic conductivity and total porosity(f),R~2=0.98.(2)The linear regression analysis of the relative gas diffusion rate in the three-dimensional measurement was carried out by one-dimensional(air chamber method)measurement of the relative gas diffusion rate,and the three-dimensional and one-dimensional measured soil relative gas diffusion rate was significantly correlated,and R~2=0.65.The relative gas diffusion rates of different texture soils under different water contents are significantly different.The relative gas diffusion rate decreases significantly as the soil water content increases.The relative gas diffusion rate of the soil is also sensitive to moisture as the water content changes.The aerated porosity of the four texture soils decreased with the increase of water content,and the soil aeration porosity was significantly different under different water contents.The sensitivity index of relative gas diffusion rate to aerated porosity in different texture soils is black soil(4.69)>sand(2.86)>loess soil(2.59)>Lou soil(2.50),It shows that black soil has the highest sensitivity to aerated porosity,followed by sand and loess soil,and the lowest of Lou soil.(3)There is a significant logarithm correlation between soil saturated hydraulic conductivity and gas diffusion rate,and a best fitting model is given.The soil saturated hydraulic conductivity can be predicted by measuring the relatively simple relative gas diffusion rate.When the water content is 0.13,0.19 and 0.27,the predicted effect is better.As long as the water content is not too high or too low,the saturated water conductivity can be derived from the relative gas diffusion rate.Since the relationship derived from this paper is based on the measured data of Lou soil,loess soil,sandy soil and black soil,the scope of the study is small,and the general applicability of the proposed method remains to be studied.