Characterization of soil organic carbon in long-term amendment trials

In the current study, total organic carbon (TOC) analysis and spectroscopic characterization (IRMS, DRIFT, and SERS) are applied to investigate the molecular changes in humic acids (HA) extracted from soil samples amended for more than 30 years with cattle manure (CM), cow slurries (CS), and crop residues (CR). All samples are compared to the unamended (T) sample. A variation in soil TOC percentage occurs in all samples, but a significant (P < 0.05) accumulation of C is observed only in CM. The TOC delta C-13 values appeared progressively less negative in all samples with respect to T. The DRIFT and SERS analyses of HA revealed a change in oxygenate groups (such as COO- and OH) in the amendment with CS and CR. These results suggest how amendment might affect both C accumulation and the HA structure.