Chemical properties of subsurface peats and their decomposition kinetics under field conditions

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Abstract
Samples of high moor peat consisting of Sphagnum moss, high moor peat consisting of Sphagnum moss and Carex middendorffii, and low moor peat consisting of Carex spp. taken from the subsurface layers of a non-cultivated site or cultivated fields were analyzed for the content in inorganic and organic constituents, and their decomposability in soil was examined under field conditions in upland and wetland rice fields. For comparison with the peat samples, rice and wheat straw and compost were also examined. Decomposition rate constants (k) of peats mixed with soil for a single compartment exponential decay model, Y t = C 0exp(− kt), ranged from 0.0032 to 0.0096 (month−1), equivalent to 3.7-11% carbon loss after 1 year, and the decomposition was enhanced by mixing with soil. Changes in the amounts of nitrogen of the peat materials were also fitted to the model and gave rate constants (k) of 0.0015-0.0078, equivalent to 1.8-9.0% loss after 1 year, for samples mixed with soil. The decomposition of rice straw, barley straw, and compost fitted to a model of double-compartment exponential decay, Y t = C 1exp(−k 1 t)+ C 2exp(− k 2 t). About 60% of rice straw in the paddy field and 77% of wheat straw in the upland field were decomposed as a labile fraction (C 1), respectively. The decomposition of lignin carbon accounted for the greater proportion of carbon loss from peat materials, although the decomposition rate was lower than that of saccharides. On the contrary, the decomposition of saccharides accounted for the greater proportion of the decomposition of wheat straw.