Summary
This study was carried out at Km 30 on the Manaus-Itacoatiara highway, in the state of Amazonas, Brazil, with the purpose of evaluating microorganism activity in three adjacent areas: undisturbed primary forest; secondary forest developed after clearing and burning; and secondary forest developed after clearing only. The area studied is an equatorial humid forest, with the soil classified as oxisol. The annual mean temperature is 26,7°C and annual mean precipitation is 1.650mm, with drought in September. Microorganism activity was measured by soil respiration with the "inverted box" method, and the "cotton buried" method determined the rate of cellulose decomposition. The secondary forest developed after daring and burning had higher microorganism activity than the secondary forest developed after clearing only. The undisturbed primary forest had the least microorganism activity. In this paper the influence of soil management on the activity of soil microorganism and on crop production is discussed.