A PRIMARY STUDY OF PERMEABILITY OF STRUCTURELESS SOIL TO AIR

The object of this work was an investigation of the relationship between soil moisture content and soil aeration in the structureless soils,and a theore- tical consideration was proposed out:For a given moisture content,the water which enters the soil must not displace the volume of air equal to that of the water which penetrates the soil,and the decrement of permeability of soil to air will not be found to bear a linear relation to the increment of the water content,however,the permeability also probably increases as the soil is wet- ted.All of this has been proved by the experiment.Furthermore,the results of the experiment showed that until the moisture content of the soil increased up to the level 33—4.5% the antipode of the moisture content and soil aeration in structureless soils then would be ture.It has been suggested that this could happen in the so-called ideal structureless soils(soil without non-capillary pore space)only.Under natural conditions,however,in author's opinion,the anti- pode of soil moisture content and soil aeration in structureless soils will not be so seriously as we generally had thought of. From the viewpoint of Agronomy,further studies about the physical pro- perties of structureless soils with relation to the permeability of soil to air was also made.The results,obtained in the experiment showed that the air per- meability of soil would be a function of the soil noncapillary pore volume,but with no linear relation to the total pore space.If the texture of structureless soil is heavier,then the air permeability will be lower.It also showed that the permeability of air flow through soil columns was inversely proportional to the depth of the column and was proportional to the depth of the soil made loose. Experiment also showed that even a thin compressive soil layer is sufficient to restrict air movement through the system.All of this is in accordance with the materials of literatures so far have touched. A coefficient PA was proposed out to represent the permeability of soil to air.It has been suggested that this coefficient could be used as an index of soil aeration,the method used to derive this coefficient has been given in de- tails in the paper.