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Temperature and duration of extraction affect the biochemical composition of soil water-extractable organic matter

Chantigny, M.H., Harrison-Kirk, T., Curtin, D., Beare, M. (2014). Temperature and duration of extraction affect the biochemical composition of soil water-extractable organic matter, 75 161-166. http://dx.doi.org/10.1016/j.soilbio.2014.04.011

Abstract

Water-extractable organic matter is regarded as readily available substrate for soil microbes. However, little is known about the influence of extraction temperature and duration on its biochemical composition. The effect of temperature (20 vs. 80°C) and extraction duration (1-24h) on the amounts of water-extractable organic C (WEOC), water-extractable organic N (WEON), carbohydrates, phenolics, ninhydrin-reactive organic N (NRON), and mineral N were evaluated using four agricultural soils from New Zealand and eastern Canada. More WEOC and WEON were extracted in hot than in cold water, and the same was found for all biochemical compounds tested. Biochemical components increased rapidly during the first 4h of extraction at 80°C, and at a slower rate thereafter. In contrast, at 20°C, concentrations of all measured components were at or close to their maximum after 1h and showed little change thereafter. Glucose and nitrate in the 20°C extracts both declined substantially between 1 and 24h, likely due to microbial activity. Moreover, the disappearance of glucose induced a decline in the ratio of carbohydrate-C to phenolic-C. The carbohydrates measured in water extracts at both temperatures were predominantly of microbial origin after 1h. However, the proportion of microbial carbohydrates gradually declined and the proportion of plant carbohydrates increased from 1 to 24h at 80°C. Based on these findings, we recommend limiting extractions to 1h or less at 20°C and to 4h or less at 80°C to minimize compositional changes that may occur during longer extraction periods. © 2014.

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