Biochemistry and distribution of deep soil C under conservation management

Authors: Stewart, Catherine; Manter, Daniel; Delgado, Jorge; Del Grosso, Stephen - Steve; Calderon, Francisco

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/9/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: N/A

Technical Abstract: Conservation agricultural management can increase surface soil C storage yet the direction and magnitude of profile soil organic C (SOC) change is determined by deep soil layers (>10cm). Mineral-associated C increases in age and depth in the soil profile and thought to be comparatively stable. However, in irrigated calcareous soils, DOC interactions with organic matter-mineral interactions may be much more dynamic. Deep SOC could be vulnerable to decomposition through priming from the addition of new, labile organic C. We used stable and radioactive isotopic, spectroscopic (FTIR) and thermogravimetric techniques to examine long-term soil C dynamics (organic and inorganic) at baseline and 13 years after conversion to no-tillage (NT) under two nitrogen fertilizer rates (0 or 220 lbs a-1). We measured d13C of SOC and SIC, 14C, and organic and inorganic chemical composition by FTIR the soil profile (0-4’). Conversion to NT and N fertilization increased surface SOC stocks, but both d13 SOC and 14C data indicated a loss of OC and increased turnover at deeper depths (>3”). Soil inorganic C increased slightly at the two deepest depths, which was confirmed by FTIR. The d13SIC suggested disequilibrium of C sources with carbonate minerals after only 13 years. These results indicate that in irrigated systems, deep soil C (both organic and inorganic) is surprisingly dynamic and susceptible to loss, despite conservation management practices.