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The use of tracers to determine the dynamic nature of organic matter




van Veen, J. A., author
Paul, Eldor A., author
[International Society of Soil Science], publisher

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Early experiments with 13C, 14C and 15N established the high rate of internal cycling of soil organic matter and reintroduced the concept of an active and passive phase in soil humus turnover. Later studies confirmed non-tracer investigations indicating that the percent decomposition of added materials is relatively independent of the rates of addition but dependent on its form and composition. The initial decomposition rate, plus the stabilization of microbial products in soil, must be taken into account when interpreting degradation of 14C enriched straw, roots, microbial tissue and specific components or in carbon dating naturally occurring 14C. Where initial decomposition data could be described by first order kinetics we calculated decay rate constants with and without the consideration of biosynthesis. Decay rates for laboratory systems were twice those for tropical field soils and eight times those calculated for temperate climates. The data were used in a model incorporating the concepts of microbial biosynthesis and recalcitrant and decomposable soil organic fractions which can both be physically protected. This realistically described the behaviour of soil-C in a Canadian grassland before and after cultivation.


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plant decomposition
organic matter
tracer research


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