Effect of repeated drying at different temperatures on soil organic matter decomposition and characteristics, and on the soil microflora

Abstract

Samples of a slightly acid sand soil were subjected to frequently repeated cycles of drying (85 or 30°C), moistening and incubation (29°C, 4 weeks). During about 60 cycles the loss of carbon, as CO₂, from the samples dried at 85°C, 30°C and the undried ones was found to be 31.2, 18.0 and 17.0%. respectively. A complete depletion of degradable material was not achieved after 60 drying-wetting cycles. After 60 cycles the 85 C-samplcs still showed the highest CO₂-production. The microbial population was reduced in numbers and species in all samples. The highest numbers of bacteria and fungi were found in the samples originally dried at 85°C. However, only a relative low proportion of these microorganisms could grow on less easily accessible substrates. Data on changes in the pH and on the C/N ratio of the organic matter are discussed, together with possible ways in which organic matter becomes available during heating.