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Microbial Mobilization of Calcium and Magnesium in Waterlogged Soils¹

ABSTRACT

Microbial mobilization of Ca and Mg was studied in 12 California soils amended with 0.5% glucose solution and incubated in air and anaerobically for 2 weeks under waterlogged conditions in the laboratory. Incubation in air resulted in a decrease of 1 to 2 units in the pH of soil solutions relative to control soils incubated without glucose. This was accompanied by 2.4- to 29.4-fold increases in the Ca content and 0.7- to 41-fold increases in the Mg content of soil solutions. A similar decrease in pH was observed under anaerobic incubation as well as 2.7- to 15.3-fold increases in the Ca content and 1.5- to 47-fold increases in the Mg content of soil solutions.

The rates of Ca and Mg release differed in soils incubated in air or under anaerobic incubation. In air the quantities of Ca and Mg in soil solutions increased for the first 3 to 10 days, then decreased. Under anaerobic incubation Ca and Mg concentrations either reached maximal values in 7 to 10 days with no subsequent decrease, or continued to increase for the duration of the experiments. The changes under anaerobic and air incubation conditions may be attributed to microbial production of a variety of organic metabolites from glucose which may be responsible for the release of Ca and Mg from exchange sites and other mineral reservoirs. These metabolic products probably are relatively stable under anaerobic incubation but become susceptible to subsequent biodegradation in the presence of air.

Key Words: glucose • soil metabolism • water hardness • exchangeable soil cations

¹ Contribution from the Extraterrestrial Res. Div., Ames Res. Center, NASA, Moffett Field, CA 94035.

² Research Scientist and Research Microbiologist, respectively, Extraterrestrial Res. Div., Ames Res. Center, NASA, Moffett Field.

Received for publication February 1, 1979.