Measurement and interpretation of air permeability coefficients in six Swedish soils
1990
Lindstroem, J. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Markvetenskap) | Jonsson, B. | McAfee, M.
The air permeability coefficient (ka) of 6 arable soils was measured throughout the growing season by a field and a laboratory method. The laboratory method gave consistently higher values of ka than the field method in all cases. Best agreement was obtained between results from the two methods in poorly permeable soil layers and worst in permeable layers overlying poorly permeable. The coefficient ka increased with increasing air content (Eg) of a particular soil type. At any particular value of Eg, the heavy clays were most permeable and sand and peat soils were least. In absolute terms, however, the Eg was much greater in the peat and sand. At a soil water content equivalent to 1.0 m drainage, ka was inversely related to clay content above a critical level of 40% clay. As the soil dried, however, the range of the apparatus was exceeded. Throughout the season, ka was approximately proportional to soil water deficit in a clay, while the converse was true for a peat. In a silt, ka decreased when weather conditions likely to cause surface crusting occurred. A comparison of the terms ka/Eg and ka/E2g allowed differences in ka due to pore size distribution and pore tortuosity to be differentiated and showed the relatively poor permeability of sandy soil to be due to high tortuosity in pores
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