Researchers analyzed soil organic carbon contents and depths of Ap horizons (i.e., cultivated topsoil) from Ontario soil survey reports from 1950 to 2019.
Soil organic carbon content: Decreases partly attributed to dilution by increased depth of cultivation in southern Ontario
Organic carbon concentrations have declined from 2.85% to 2.34% in Ap horizons while depths have increased by 40%. Considering the entire Ap horizon depth, we show that soil carbon stocks (kg C ha-1) may be constant or increasing. Losses of organic carbon due to cultivation should not be discounted; however, dilution of organic carbon within a deeper plow layer may contribute significantly to observed decreases in organic carbon concentrations in topsoil.