Physical factors influencing decomposition of organic materials in soil aggregates

• Published in: Soil biology & biochemistry Vol. 10; no. 2; pp. 109 - 115
• Main Authors: Adu, J.K., Oades, J.M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1978
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(78)90080-9

Glucose or starch labelled with 14C was mixed thoroughly into slurried soils. Aggregates of different sizes were obtained from the soils as they dried. The labelled substrates were considered to be distributed in both micro- and macropores in the aggregates. Control samples (labelled substrates in macropores only) were prepared by adding the labelled carbohydrates after the formation of the aggregates. The various samples were sterilized by γ-irradiation and stored at −15°C. Samples were wetted to about −20kPa, inoculated with soil organisms, and incubated for 4 weeks at 28°C in closed systems, which enabled regular measurement of 14CO 2 released. Based on the 14CO 2 released, it was concluded that starch was protected from microbial attack when present in micropores in aggregates made from fine sandy loam. After incubation samples were dried and rewetted. The flush of 14CO 2 released was twice as big for samples containing labelled starch compared with glucose, showing that disruption of aggregates, containing residual starch, and rearrangements of soil components are as important as chemical and biological factors in causing the flush of CO 2 resulting from wetting a soil. Mechanical disruption of the aggregates resulted in a similar flush of 14CO 2.