TEMPERATURE EFFECTS ON ORGANIC-MATTER AND MICROBIAL BIOMASS DYNAMICS IN TEMPERATE AND TROPICAL SOILS

The aim was to investigate whether soils developed under tropical cond itions had different organic matter and microbial biomass dynamics tha n soils developed under temperate ones. Three soils formed under tempe rate climatic conditions (U.K.) and three under tropical conditions (B razilian) were selected to be as comparable as possible in terms of or ganic matter, clay content and pH. They were then incubated moist at 1 5 degrees C or 35 degrees C for 150 d. Carbon dioxide evolution and mi crobial biomass were measured at intervals during the incubation. The biomasses in the tropical soils declined more slowly at both temperatu res than in the temperate soils, although at 15 degrees C the differen ces were mainly small. At 35 degrees C the decline was generally much more marked in the temperate soils (60-75% of the initial value) than in the tropical ones (15, 40 and 60%). Soil organic matter was mineral ised more rapidly in the temperate than the tropical soils: at 35 degr ees C up to 9-10 times more CO2-C was evolved than was contained in th e temperate biomasses during the 150 d incubation. The comparable maxi mum value for the tropical soils was 4.5 times. These results seem to indicate that the organic matter in the tropical soils was more degrad ed, or humified, than that in the temperate soils. An attempt to quant ify the extent of humification was made using differential thermal ana lysis (DTA) and thermogravimetric analysis (TG). Both methods also ind icated that the organic matter was generally more humified in the trop ical than temperate soils. It was concluded that DTA and TG may both b e useful techniques in studying soil organic matter dynamics, especial ly when linked to studies of soil microbial dynamics. (C) 1998 Elsevie r Science Ltd. All rights reserved.