Study On The Measuring And Calculating Methods Of Soil Air Permeability

Based on the analysis of theory and infiltration experiments in the field, the thesis is toinvestigate the soil air permeability’s factors，and to discussion soil air permeability’srelationship with water conductivity. On the other hand, this paper analyze and compareseveral measurement methods of soil air permeability in common use，and on the basic of thelength equivalent principle, the transient air permeability model is deducted in thethree-dimensional transient boundary conditions. The results are as follows:1. Partial correlations analysis was performed among the soil air permeability, soil watercontent, soil porosity using SPSS for windows, and there are very significant correlationamong them. In addition, because of the needs of agricultural, the fertilizers for differentuses,methods of cultivation, as well as soils which live microorganism have influence on thepore tortuosity-connectivity, that lead to differences of soil air permeability among differenttypes of soil using.2．The logarithmic expression betweenk_aandk_sshould be fitted according to thepractical soil. In addition, the fitted logarithmic expressions with low relative error in thispaper are adapted to the apple orchard in Yantai.3.This paper deals with the comparation between the one-dimensional constant pressuremethod and the one-dimensional transient-flow method in measuring air permeability,analyzing the merits and demerits of the two models in efficiency and economy, as well as therange ability in relative error of the measuring result.The outcome indicts that the constantpressure method and the transient-flow method for measuring air permeability have apparentcorrelativity, which could be demonstrated by the linear function formula y=0.9791x. Takeconstant pressure method as a standard, the relative error range ability of the two methodsmeasurement result is between0.5%and45%, more than80%of measurement result’srelative error range ability is less than15%.4. This paper try to simplify the calculation process of parameter s based on one-dimensionaltransient-flow model and then test it by steady-state method. Through the40soil sample’smeasurement indoors, the outcome indicts that the tank pressure lnp（t） vs. time data have stillapparent correlativity. For the same sample, the transient-flow method calculated bysimplified solution s₀and the constant pressure method in measuring air permeability haveapparent correlativity, then the coefficient of correlation R=0.93. Meanwhile, if take parameters s as a standard, the relative error range ability of Parameters s and simplifiedsolution s₀is under0.5%, therefore，the two numerical value are approximate.5. Suppose the tank pressure vs. time data still existed under the three-dimensional transientboundary conditions，its quantitative relationship with air permeability is analyzed，and thesoil air permeability of apple orchard in Yantai Academy of Agricultural Sciences iscalculated，which is verified by steady-state method．The results showed that the tank pressurevs. time data still existed under the three-dimensional transient boundary conditions，moreover，there are very significant correlation between quantitative relation air permeabilitycalculated result and the three-dimensional steady-state model’s measured result，while thecorrelation coefficient was0.93．According to Yantai orchard soil air permeability，therelative error range ability of the measured result between the empirical formula andthree-dimensional steady-state model is small，and more than70%of measurement result’srelative error range ability is less than25%. These indicated that the empirical formula hasrepresentative．6. The range of gas motion outside of Soil column, which was difficult to measure directly inthree-dimensional boundary conditions, was defined according to the length equivalentprinciple. Under such circumstance, the transient air permeability model is deducted in thethree-dimensional transient boundary conditions and verified by steady-state method. Outdoortest results show that the new model can be used to calculate the soil air permeabilityaccurately. Moreover, there are extremely significant correlation between new model’s airpermeability measured results and the three-dimensional steady-state model’s measuredresults. Take the result of three-dimensional steady-state model as a standard, the relativeerror range ability of the measured result between the new model and three-dimensionalsteady-state model is small, and more than80%of wheat fields measurement result’s relativeerror range ability is less than15%, while more than75%of apple orchards measurementresult’s relative error range ability is less than20%.