Experimental Studies On Soil Air Permeability

Review of research results of soil air permeability in the home and abroad,the thesis is to investigate the soil air permeability:its factors,its daily change through all-day observations, and its relationship with water conductivity in three different soils.In addition,the pore tortuosity-connectivity parameter was also analyzed and the values that adapt for each experimental field were proposed.The results are as follows:1.The soil air permeability decreases with the increase of water content.Under the same water content,it decreases with the increase of bulk density.Under the same bulk density,the soil air permeability of horizontal soil samples is higher than that of vertical soil samples;the soil air permeability of high radicle content samples is higher than low radicle content samples.2.There are differences on the soil air permeability among various biomes.Because of the needs of agricultural production,the fertilizers for different uses,methods of cultivation as well as holes which live ants and earthworms have an influence on the pore tortuosity-connectivity,that lead to differences of soil air permeability among different types of soil using.Soil crust also has an evident influence on soil air permeability.3.The research on features of soil air permeability and water conductivity of both disturbed and undisturbed soils,shows that both of soil air permeability and water conductivity of undisturbed soils is higher than that of disturbed soils.And the reason is that the destruction of soil structures changes its pores,especially the existing of large pores,which further confirms that soil structures and pore features have heavy influence on the transport of water and gas in soil.By analyzing the relative permeability of undisturbed and disturbed soil samples as a function of water saturation,we could find that the tendency of these curves was same basically,but the curves were not superposition.So we could conclude that the pore tortuosity-connectivity was different between undisturbed and disturbed soils,which give us the reference of analyzing the characteristics of water conductivity and air permeability for both undisturbed and disturbed soils further in future.4.The research results in changwu shows:the soil surface air permeability of corn land and apple land varies with temperature.Corn land is more loosened than apple land,so the soil surface air permeability of former is higher than that of latter.The soil surface of apple land is harder than 5cm under soil surface of it,so the soil surface air permeability of former is lower than that of latter.Results shows soil surface air permeability of corn land and apple land exists a linear function with air temperature.However,soil air permeability of 5cm under soil surface has no relation with air temperature,but has evident relation with temperature of 5cm under soil surface.5.The research results in shenmu shows:the soil surface air permeability of different types of soil using has no relation with temperature.But all of them have the same tend of variation, which builds the forecast relationship based on the soil surface air permeability of grass.The soil surface air permeability of different types of soil using exists a linear function with its water conductivity.The different slope location of the same type of soil using also has an impact on soil surface air permeability.6.In 1998,Moldrup recommended the value ofη(pore tortuosity-connectivity)as 2,but it is not suitable for water-wind erosion crisscross region in north of shaanxi province, according to measurement values,my thesis gets the value ofη:3.80—3.95.The pore tortuosity-connectivities of disturbed and undisturbed soils in both air and liquid differ is different.The curves of soil air permeability and water conductivity of disturbed and undisturbed soils under different water saturations do not match,it implies that although in the same water saturation,the pore tortuosity-connectivities of air and liquid differ are different. So that,it is better to distinguish the values of the pore tortuosity-connectivities between air and liquid differ,it is also better to distinguish between disturbed and undisturbed soils.7.The logarithmic expression between k_αand k_s should be fitted according to the practical soil for the reason that the soil texture has strong influence on the coefficientβ. The fitted logarithmic expressions with low relative error are adapted to changwu.It is noticed that the fitted results are influenced largely by the soil texture in the present method,and thus the soil texture should be considered.The expressions which are adapted to yangling,changwu,shenmu were presented in this paper.