The influence of moisture on microbial activity of soils

A series of microcalorimetry experiments were performed to follow the effec t of moisture on soil microbial activity. Activity was stimulated by adding a solution of 6.0 mg of glucose and 6.0 mg of ammonium sulfate in 0.80 cm( 3) of distilled water to 1.50 g of red Latosol soil. This solution represen ts the moisture used in the experimental system (MAES) which directly affec ts the microbial activity. MAES values vary from 9.1 to 50.0% in selected r eports where the humidity was not taken into account in calorimetric determ inations. In this study, the thermal power caused by microbial activity was followed in samples of red Latosol with MAES values of 34.78%. In soil wit h absolute humidity values varying between 36.74 to 37.74%, the total heat reached a maximum value, 15.92 J g(-1). A drastic decrease above absolute m oisture values of 41.82% was observed. The methodology with 34.78% MAES val ues showed a better microbial activity on soil than lower values of humidit y. The proposed methodology establishes a defined MAES value of 34.78% to o ptimize the calorimetric results obtained from air-dried soil experiments. (C) 1999 Elsevier Science B.V. All rights reserved.