Influence of Calcium Carbonate and Charcoal Applications on Organic Matter Storage in Silt‐Sized Aggregates Formed during a Microcosm Experiment

Silt‐sized aggregates (2–53 μm) can store a high percentage of organic matter (OM) in agricultural soils. This study aimed to determine whether additions of charcoal and CaCO 3 may enhance the retention of organic C (OC) and total N (N t ) in silt‐sized aggregates. We used artificial soil mixtures without a silt component (89% sand, 10% clay, 1% OM) to emulate sandy soils with little natural structure. Charcoal and/or CaCO 3 were added, and the resulting mixtures were incubated for 16 wk in the dark. The newly formed silt‐sized fraction was separated and analyzed for OC and N t concentrations and characterized using FTIR and scanning electron microscopy‐energy dispersive X‐ray spectroscopy (SEM‐EDS). Compared to the control treatment, CaCO 3 addition had no positive effects on C and N retention in the silt‐sized fraction (17–20 g kg −1 OC, 0.15–0.17 g kg −1 N t ) whereas the silt‐sized fraction from treatments with charcoal additions showed significantly higher OC and N t concentrations (50–56 g kg −1 OC, 0.31–0.85 g kg −1 N t ). Silt‐sized fractions from the charcoal treatments also showed a significant increase in the proportion of C=O groups. These initial results justify more detailed investigations into the improvement of the structure and nutrient retention of sandy soils by charcoal and CaCO 3 applications.