Soil C dynamics below the plow layer have been little studied, in spite of proven large C stocks and suspected large C stabilization potential. The objective of the present study was to determine C‐turnover kinetics throughout the 1‐m profile of a cultivated loam soil of the Paris basin, France. The soil 13C signature was determined to depths of 1.05 m in 32 replicated plots having received from 0 to 10 yr of maize after wheat. Above‐ and below‐ground maize‐residue biomass inputs were estimated throughout the 10‐yr period. After 10 yr, maize‐derived soil organic carbon (SOC) constituted about 10, 5, and 2% of the total SOC at 15‐, 50‐, and 100‐cm depths, respectively. About one‐third of recently deposited maize‐derived SOM present in the 1‐m soil profile was retrieved below the Ap horizon. The ratios of maize‐derived soil C to the cumulative maize above‐ and below‐ground inputs over the 10‐yr period averaged 17% across the soil profile. This ratio was lower in the Ap horizon (i.e., 13%) than in deeper soil horizons. Circumstantial evidences suggest that the distribution profile of recently deposited maize‐derived C was influenced by fine root activities, bioturbation, and dissolved organic carbon (DOC) transport, the latter being substantiated by a high correlation (r2 = 0.86) between SOC contents and amorphous Fe + Al contents. In conclusion, our study stresses the need to take into account the full 1‐m soil profile in C sequestration studies.
Soil organic matter (OM) stabilization by the mineral phase can take place through sorption and aggregation. In this study we examined both of these processes, (i) organic carbon (OC) sorption onto clay-sized particles and (ii) OC occlusion in silt-size aggregates, with the objective of evaluating their relative importance in OM storage and stabilization in soil. We studied two loamy soil profiles (Haplic Luvisol and Plinthic Cambisol) currently under agricultural use down to a depth of 2 m. Our approach was based on two parallel fractionation methods using different dispersion intensities; these methods isolated a free clay fraction (non-occluded) and a clay fraction occluded within water-stable silt-size aggregates. The two clay fractions were analysed for their C content and 14 C activity. The proportion of sorbed OC was estimated as OC loss after hydrofluoric acid (HF) demineralization. Our results showed an important contribution to SOM stabilization by occlusion of OC into silt-size aggregates with depth through both soil profiles. In the Haplic Luvisol, OC associated with clay and located in silt-size aggregates accounted for 34-64% of the total soil OC, whereas in the Plinthic Cambisol this occluded material represented 34-40% of total OC. In the Haplic Luvisol, more OC was located in silt-size aggregates than was sorbed onto clay-size minerals, suggesting that silt-size aggregation plays a dominant role in OC storage in this soil. In the Plinthic Cambisol, the abundance of sorbed OC increased with depth and contributed more to the stored C than that associated with silt-size aggregates. Radiocarbon dating of both clay fractions (either occluded within silt-size aggregates or not) suggests, in the case of the Plinthic Cambisol, a preferential stabilization of OC within silt-size aggregates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.