Ecosystem biogeochemical fluxes are consequences emerging from the various biotic and abiotic interactions in an ecosystem. Among the many different ways in which organisms interact, substrate competition as constrained by the abiotic environment is the first critical step to fulfill an organism's metabolic demand. Therefore, it is critical to consistently represent substrate competition for a credible and robust modeling of ecosystem biogeochemistry. We previously showed that by assuming quasi-steady-state and recognizing the conservation of mass and competitor surfaces, the various biological and non-biological competitors and substrates could be summarized into an Equilibrium Chemistry Form (ECF). Under the additional assumption of non-overlapping binding, we obtained the Equilibrium Chemistry Approximation (ECA) kinetics from the ECF. We here report that the ECA kinetics is superior to the classical Michaelis-Menten kinetics in representing substrate-microbe interactions during litter decomposition and the ECA enables a reasonable modeling of lignin decomposition dynamics whereas the Michaelis-Menten kinetics fails. We also applied the ECA kinetics to represent nutrient competition between plants and microbes in a soil biogeochemistry model, and our results indicated significant improvements over existing approach used in CLM4.5 and ALM. We are therefore integrating ECA kinetics in ALM to improve biogeochemical modeling and its impacts in the coupled Earth System.