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Air Turbulence Effects upon Soil Gas Exchange¹

ABSTRACT

The effects of air turbulence upon the exchange of gases between a soil and the atmosphere were investigated using a specially designed vapor exchange meter. The device measured the rate of evaporation of liquid heptane from a porous stainless steel plate buried in a porous medium. Natural air turbulence as indicated by both mean windspeed and root mean square air pressure fluctuations significantly affected the heptane evaporation rates in straw and coarse gravel, but had a decreased effect in media of smaller pore size. In silt loam, the regression coefficient for evaporation rate on windspeed was 20% of its value for straw. Increasing depth from 1 to 8 cm in coarse sand caused a 91% decrease. Although the heptane flux values are quite scattered, the data indicate that air turbulence can significantly increase the transport of water vapor through coarse mulches or through very shallow depths of soil, but that soil aeration is mostly a diffusive process.

¹ Contribution from the Northeast Branch, Soil and Water Conservation Res. Div., ARS, USDA, in cooperation with N. Y. State Agr. Exp. Sta. at Cornell Univ. This paper is a portion of the thesis submitted by the senior author in partial fulfillment of the Ph.D degree at Cornell Univ. Agronomy Series Paper no. 890.

² Formerly graduate student (now Research Soil Scientist (Physics), USDA, Water Conservation Laboratory, Phoenix, Ariz.) and Research Soil Scientist (Physics), USDA, and Professor, Agronomy, Cornell Univ., Ithaca, N.Y.

Received for publication June 8, 1970. Accepted for publication September 9, 1970.