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

Abstract

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 CaCO3 may enhance the retention of organic C (OC) and total N (Nt) 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 CaCO3 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 Nt concentrations and characterized using FTIR and scanning electron microscopy‐energy dispersive X‐ray spectroscopy (SEM‐EDS). Compared to the control treatment, CaCO3 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 Nt) whereas the silt‐sized fraction from treatments with charcoal additions showed significantly higher OC and Nt concentrations (50–56 g kg−1 OC, 0.31–0.85 g kg−1 Nt). 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 CaCO3 applications.