Natural 13C abundance: a tool to trace the incorporation of dung-derived carbon into soil particle-size fractions.
During the decay of 13C enriched dung patches, the; delta 13C 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 (delta 13C = -15.36/1000) or ryegrass (delta 13C = -25.67/1000), 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 (< 0.2 micron) and coarse clay (0.2-2 microns), silt plus fine sand (2-250 microns), and coarse sand (250-2000 microns), and analyzed for total C, N, and delta 13C. As particle-size diameter decreased, the C/N ratios decreased and delta 13C 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 microns fractions during the whole experiment. The proportion of dung-derived C in the fine clay peaked 42 d after dung application, coinciding with the delta 13C 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 < 0.2 micron fractions and continuous accumulation of particulate C (> 250 microns).
Institute of Soil Science and Soil Geography, University of Bayreuth, Germany. wulf.amelung@uni-bayreuth.de
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D000821:Animal Feed; D000818:Animals; D002244:Carbon / Q000032:analysis; D002247:Carbon Isotopes / Q000032:analysis*; D002417:Cattle; D005243:Feces; D008297:Male; D013058:Mass Spectrometry; D009584:Nitrogen / Q000032:analysis; D006109:Poaceae; D012987:Soil / Q000032:analysis*
D002247:Carbon Isotopes; D012987:Soil; D002244:Carbon; D009584:Nitrogen