Kirchmann, Holger
- Department of Soil Sciences, Swedish University of Agricultural Sciences
Abstract
The soils varied with respect to historical land-use (heathland, plaggen-manuring, woodland) and soil genetic factors (podzolization, groundwater). Data from long-term experiments on sand and sandy loam were also considered. The soils revealed a wide range of OC content from below 10 to about 50 mg g(-1). C to N ratios varied between 10 and 30 and were positively linked to total OC (R(2) = 0.87). Graphitized C ('charcoal', as H(2)O(2)-resistant fraction) was of minor importance, with just about 0.5 mg C g(-1) soil in most samples. Only some plaggen and-heath soils had charcoal C contents around I and 1.5 mg g-1 but this was still less than 5% of the total OC. The HCl-resistant C fraction, on the other hand, was extremely large, amounting to 50-90% of the total OC. Its percentage was closely related to total OC (R(2) = 0.84). Biomass C contents (fumigation-extraction) were not correlated with total OC. The C-rich soils had low biomass C to total OC ratios (< 0.005). The activities of the enzymes catalase and dehydrogenase showed similar relationships. This strongly indicated that major proportions of the organic material do not support a microbial population and are not in a process of net-decomposition. The average respiration rates per unit of OC after 100 days of incubation at 20 degreesC were lowest in the C-rich samples. Water soluble organic carbon (WSOC) increased slightly with total OC. On an average, a sum of 379 +/- 80 mug C g(-1) soil was obtained over seven sequential extractions. This was about the same amount as respired in 140 days (373 +/- 107 mug CO(2)-C g(-1)) but there was no significant correlation between the respired CO(2)-C and the extracted WSOC. The steady-state rate of WSOC released (steps 3-7) per unit of total OC was lowest in the C-rich soils, again indicating the high stability of OC. We concluded that, old sandy Ap horizons soils may have high levels of OC with high proportions of very stable (refractory) constituents amounting to more than 50% of total OC or 10-30 mg C g(-1) soil. (C) 2002 Elsevier Science Ltd. All rights reserved.
Keywords
refractory organic matter; sand; heathland; plaggen; podzolization
Published in
Soil Biology and Biochemistry
2002, volume: 34, number: 11, pages: 1571-1581
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
SLU Authors
UKÄ Subject classification
Soil Science
Publication identifier
- DOI: https://doi.org/10.1016/S0038-0717(02)00127-X
Permanent link to this page (URI)
https://res.slu.se/id/publ/44193