Long-term effect of lime application on the chemical composition of soil organic carbon in acid soils varying in texture and liming history

There is ample evidence to suggest that liming can regulate soil organic carbon (SOC) pools either directly through influencing the solubility of SOC or indirectly by altering total organic C input as crop residue and SOC loss via change in microbial activity. The aim of this study was to determine the long-term impact of lime application on the quantity and quality of SOC in acid soils. Soils were collected at depths of 0-10, 10-20, 20-30, 30-40, and 40-50 cm from four long-termlime trials with various lime rates (0-25 t ha−1), lime histories (5-35 years), and soil textures (clay content 5- 36 %). Surface application of lime was effective in ameliorating both topsoil and subsoil acidities at sites with low clay content. Liming decreased dissolved organic C (DOC) at 0- 30 cm but increased its aromaticity. Total SOC at 0-10 cm decreased or remained unchanged following long-term liming, depending on the rates of lime application and crop management. Changes in the contents of particulate organic C (POC) and humic organic C (HOC) predicted by midinfrared spectroscopy (MIR) and partial least squares regression (PLSR) showed a similar trend to total SOC at all sites. Lime application had no significant effect on SOC below 10- cm layers and on the MIR-predicted resistant organic C (ROC) fraction. Solid-state13C nuclear magnetic resonance (NMR) spectra indicated that the alkyl C content and alkyl/O-alkyl C ratio were lower in the limed than unlimed plots. Liming possibly had a marked effect on regulating the decomposition and preservation of certain C compounds. The apparent accumulation of alkyl C in the unlimed soil could indicate the potential ability of acid soils to store SOC.