Application of cattle manure increased the stability of organic carbon in the subsoil in Mollisols

Application of cattle manure could improve soil fertility by increasing the stability of soil organic carbon (SOC), however, the extent of this effect might depend on the soil layer. This study aims at evaluating the differences in SOC chemistry between topsoil and subsoil caused by cattle manure addition.

Here, a 90-day pot experiment was used to investigate the SOC chemical structure (¹³C-NMR and FTIR), as well as microbial community composition (PLFA), with cattle manure amended in topsoil (T1M) and subsoil (T2M) and without manure in topsoil (T1) and subsoil (T2).

Application of cattle manure significantly increased SOC, total nitrogen (TN) contents and plant biomass either in topsoil or subsoil. The alkyl C/O-alkyl C (A/OA) ratio of T1M was lower than that of T1, while T2M was greater than that of T2, indicating the SOC of T1M decomposition was delayed but of T2M was promoted. The A/OA ratio of T2M was greater than that of T1M, indicating the decomposition degree of SOC of T2M was greater. The fungi/bacterial PLFA ratio, G⁺/G⁻ PLFA ratio and fungi PLFA were lower in T2M than T1M. RDA analysis demonstrated that O-alkyl C was negatively associated with bacterial and G- PLFA, especially Gemmatimonadetes and Acidobacteria, while positive correlation with fungi PLFA. However, the alkyl C was negatively associated with fungi PLFA, especially Basidiomycota.

The subsoil with cattle manure added promoted bacterial consumed labile C, especially Gemmatimonadetes and Acidobacteria. Therefore, the subsoil with cattle manure added had a higher decomposition degree of SOC when compared with the topsoil with cattle manure added, improving the stability of SOC.