Degradation Rate Model Formulation to Estimate Soil Carbon Sequestration from Repeated Biosolids Application

Land application of biosolids is a process that increases the amount of soil C sequestration and may produce C credits in accordance with the definition of United Nations Climate Change Convention. A dynamic degradation rate model (DRM) provides insights on C sequestration due to microbial biomass, soil organic carbon (SOC), CO2 emission rates, residence time of sequestered C, and biomass to biosolids ratios. We employed a 34-yr biosolids application database from the literature to determine the amount of C sequestered in 41 strip-mined Illinois fields. This database is used to formulate the DRM using curve fitting techniques. Degradation rate model applications identify two SOC phases in soil. Soil organic C gain in Phase 1 (first 10 yr) is primarily due to biosolids application while in Phase 2, SOC gain is due to biomass or C sequestration. Carbon sequestration changes with time relate to variations in biosolids application amounts (10 and 18 Mg ha-1 yr-1), different degradation rate constants (0.04–0.16 yr-1), and biomass yields (35–40%). Additionally, the degradation rate constant is correlated positively with the C application rate for a period of 34 yr. Based on the 34-yr database, the DRM simulates the process that decomposes SOC produced by biosolids application into C in biosolids that have not been degraded and C in biomass produced during the microbial degradation process. The DRM quantifies the biosolids degradation rate constant and biomass yield, and provides an easy quantitative method for evaluating C credits from biosolids added to soil.