Marc G. Kramer

We were interested in studying changes in the dynamics of soil organic matter (SOM) chemistry with depth and across sequential density fractions. Changes in the chemical composition of SOM with depth were examined in two Oxisol soil depth profiles. We used a sequential density fractionation (DF) technique to look at changes in C and N content and stable isotope composition (15N, 13C) of sequentially deeper and denser soil fractions. For each depth sample, we collected six 10 cm soil cores--two from each of three soil profile walls in the pit. Four density fractions per soil depth for 7 depths (a depth to 10 cm for the first two mineral samples, then in 20 cm intervals thereafter) were examined up to 1.2 m within the soil profile. The overall soil depth profiles revealed a trend of both decreasing C/N values and C content, a soil depth profile pattern which has been commonly observed across a range of soil types. Our results suggest microbially processed materials accumulated with de...