Soil organic matter dynamics in a grazed pasture
Cyle, Kevin Taylor
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Increasing soil organic matter (SOM) persistence through land management requires a better understanding of the mechanisms that control soil organic matter dynamics. The conversion of row-crop agriculture to management intensive grazing (MiG) agriculture systems in the southeastern US can result in substantial accumulation of SOM. It is unclear how the biochemical composition of organic matter inputs influence SOM accumulation and subsequent turnover time. We hypothesized that higher quality substrates would increase SOM accumulation in more stable soil mineral fractions, despite faster initial mineralization rates. We tested this hypothesis by incubating plant and ruminally-digested residues that span a gradient of substrate quality. Our results indicate that high quality substrates are respired at higher initial rates and promote the accumulation of organic matter in silt and clay fractions. These findings suggest that the decomposition of more labile substrates preferentially produce organic matter associations in stable soil mineral fractions.