Modeling vertical movement of organic matter in a soil incubated for 41 years with 14C labeled straw

• Published in: Soil biology & biochemistry Vol. 39; no. 1; pp. 368 - 371
• Main Authors: Bruun, Sander, Christensen, Bent T., Thomsen, Ingrid K., Jensen, Erik S., Jensen, Lars S.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2007; New York, NY Elsevier Science
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; Organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Radiocarbon; Soil organic matter movement; Soil science; Vertical distribution; Vertical distribution; Radiocarbon; Soil organic matter movement; Organic matter; Incubation; Radiolabelling; Carbon Isotopes; Vertical motion; Radioisotope; Modeling; Straw; Soils; C-14; Motion study; Soil science
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2006.07.003

The distribution of organic matter (OM) in the soil profile reflects the balance between inputs and decomposition at different depths as well as transport of OM within the profile. In this study we modeled movement of OM in the soil profile as a result of mechanisms resulting in dispersive and advective movement. The model was used to interpret the distribution of 14C in the soil profile 41 years after the labeling event. The model fitted the observed distribution of 14C well ( R 2=0.988, AIC c=−82.6), with a dispersion constant of D=0.71 cm 2 yr −1 and an advection constant of v=0.0081 cm yr −1. However, the model consistently underestimated the amount of OM in the soil layers from 27 to 37 cm depth. A possible explanation for this is that different fractions of OM are transported by different mechanisms. For example, particulate OM, organomineral colloids and dissolved OM are not likely to be transported by the same mechanisms. A model with two OM fractions, one moving exclusively by dispersive processes ( D=0.26 cm 2 yr −1) and another moving by both dispersive ( D=0.99 cm 2 yr −1) and advective ( v=0.23 cm yr −1) processes provided a slightly better fit to the data ( R 2=0.995, AIC c=−83.6). More importantly, however, this model did not show the consistent underestimation from 27 to 37 cm soil depth. This corroborates the assumption that differing movement mechanisms for different OM fractions are responsible for the observed distribution of 14C in the profile. However, varying dispersion, advection, and decay of OM with depth are also possible explanations.