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The Effect of Temperature on Decomposition at Optimum and Saturated Soil Water Contents¹

ABSTRACT

A laboratory study was conducted to evaluate the effect of temperature on decomposition in a silt loam soil under saturated (0.32 g/g) and optimal (0.19 g/g) soil water contents. Sewage sludge was the carbon substrate. Cumulative CO₂-C data were obtained for three temperatures (14, 22, and 30°C), and two substrate groups (rapid, intermediate) for the saturated and optimal water contents. Decomposition followed first-order kinetics. The temperature effect for each substrate and water content was described by regressing the natural logarithm of the first-order rate constant on the inverse of the absolute temperature. No significant differences in slopes between substrates within a water content were found for these regressions. Slopes were significantly different between water contents. The slopes were –8975 and –2660 K for the unsaturated and saturated soils, respectively. At saturation the much smaller rate of change in the rate constant, k, with temperature (slope) indicated that temperature had a much smaller influence on decomposition rate under saturated than under unsaturated conditions. Intercepts from the above regressions were significantly different between substrates and water contents. For the unsaturated soil, intercepts were 25.86 and 29.41 for the rapid and intermediate substrates, respectively. Parallel intercepts at saturation were 3.48 and 2.36, respectively. Differences in intercepts between water contents combined with slopes resulted in smaller k values for the saturated soil. These results pointed out that a single equation describing the effect of temperature on the first-order rate constant should not be applied to the decomposition of organic matter in both unsaturated and saturated soils.

¹ Contribution from the Dep. of Agronomy, Univ. of Arkansas, Fayetteville, AR 72701. Published with the Approval of the Director of the Arkansas Agric. Exp. Stn.

² Graduate Research Assistant and Professor of Agronomy, respectively.

Received for publication December 13, 1982. Accepted for publication April 22, 1983.

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