CO2 evolution after straw incorporation in soil supplemented with nutrients based on C:N:P:S stoichiometry

Evidence exists for a constant C, N, P, and S content in stabilized organic carbon in soils globally. This indicates that fresh-C inputs to soil with insufficient nutrients can limit the size of the soil C pool. This study conducted an experiment to test C:N:P:S stoichiometry as a mechanism to increase the rate of organic matter (OM) mineralization following straw incorporation in soil. The objectives were to (i) determine whether straw incorporated in soil with supplementary nutrients to balance the C:N:P:S stoichiometric input would increase the rate of OM mineralization and (ii) assess the rate of OM mineralization from straw with stoichiometric nutrient input that was either N, P or S limited. Straw was incorporated in soil at a rate of 8 t ha^-1with or without supplementary nutrients to convert a target 30% fresh C-input to SOC. Five soils with increasing silt and clay content were included in the study and incubated in an environmentally controlled chamber for 16 weeks. CO₂ was collected at one or more weekly intervals in a 1N sodium hydroxide (NaOH) trap, precipitated by BaCl_2, and titrated with HCl to determine the CO₂-C evolved. A repeated measure multivariate ANOVA is being used to determine if there were differences in CO₂-C between nutrient treatments or nutrient treatments over time. Decomposition of straw was completed in 12 weeks. In three out of five soils the total CO₂-C production for a straw with stoichiometrically balanced nutrients was significantly greater (P < 0.01) than the straw with no nutrient addition. In the soils that demonstrated a greater rate of OM mineralization with nutrient supplementation, the N, P, and S limited treatments all produced less CO₂-C. Interestingly, all five soils collected for this study had a high P fertility status, yet lower CO₂-C was produced in the P-limiting treatment indicating that the soil P was not immediately available during straw decomposition. In conclusion, higher rates of OM mineralization were achieved when C-input was stoichiometrically balanced. Nutrient inputs of N, P and S could maximize the soil C sequestration potential.