Natural13C abundance: a tool to trace the incorporation of dung-derived carbon into soil particle-size fractions

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Abstract
During the decay of 13C enriched dung patches, the ;δ13C signal of surface soil (1–5 cm) increased with a temporary maximum after 42 d. To understand the underlying processes, we investigated the incorporation of dung‐derived C into soil particle‐size fractions. Dung, collected from beef steers fed on maize (δ13C = −15.36‰) or ryegrass (δ13C = −25.67‰), was applied in circular patches to a C3 pasture at North Wyke, UK. Triplicates were sampled from surface soil (1–5 cm) at 14, 28, 42, and 70 d after application, pooled, separated into fine (13C. As particle‐size diameter decreased, the C/N ratios decreased and δ13C values increased at all plots due to increasing microbial alteration of soil organic matter. After dung application, ca. 60 % of dung‐derived C in soil was recovered in the 0.2–250 µm fractions during the whole experiment. The proportion of dung‐derived C in the fine clay peaked 42 d after dung application, coinciding with the δ13C maximum in the bulk soil and the maximum leaching rate measured in lysimeters at this time in another study at the same sites. The percentage of dung‐derived C as particulate C in the coarse sand fraction increased until the end of the experiment. We conclude that incorporation of C into soil from decomposing dung patches involved both temporary sorption of leached dung C to 250 µm). Copyright © 1999 John Wiley & Sons, Ltd.