Climate feedbacks from soils can result from environmental change followed by response of plant and microbial communities, and/or associated changes in nutrient cycling. Explicit consideration of microbial life-history traits and functions may be necessary to predict climate feedbacks owing to changes in the physiology and community composition of microbes and their associated effect on carbon cycling. Here we developed the microbial enzyme-mediated decomposition (MEND) model by incorporating microbial dormancy and the ability to track multiple isotopes of carbon. We tested two versions of MEND, that is, MEND with dormancy (MEND) and MEND without dormancy (MEND_wod), against long-term (270 days) carbon decomposition data from laboratory incubations of four soils with isotopically labeled substrates. MEND_wod adequately fitted multiple observations (total C–CO₂ and ¹⁴C–CO₂ respiration, and dissolved organic carbon), but at the cost of significantly underestimating the total microbial biomass. MEND improved estimates of microbial biomass by 20–71% over MEND_wod. We also quantified uncertainties in parameters and model simulations using the Critical Objective Function Index method, which is based on a global stochastic optimization algorithm, as well as model complexity and observational data availability. Together our model extrapolations of the incubation study show that long-term soil incubations with experimental data for multiple carbon pools are conducive to estimate both decomposition and microbial parameters. These efforts should provide essential support to future field- and global-scale simulations, and enable more confident predictions of feedbacks between environmental change and carbon cycling.

Core Ideas: After 3 yr, soybean yield was higher from multispecies than from single‐ and double‐species cover cropping. Multispecies cover cropping had higher soil water and inorganic N content than less‐diverse treatments. Soil organic C was unaffected by cover crop species diversity. Several years of cover cropping are needed to achieve ecosystem benefits. Multispecies cover cropping has become popular in recent years because of the multiple ecosystem benefits compared with single‐ or double‐ species cover cropping. However, scientific studies on the effects of multispecies cover cropping—especially in the southern United States—are limited. A field study was initiated in 2013 at the University of Tennessee's Research and Education Center in Milan, TN, to assess the agronomic and soil responses from single‐, double‐, and multispecies cover cropping in corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] systems. After 3 yr, we found that a multispecies mixture of legumes, grasses, and Brassica spp. significantly increased soybean yield, gravimetric soil water content, and soil inorganic nitrogen as compared to the less‐diverse treatments and a no‐cover control. However, after 3 yr, cover cropping did not increase soil organic carbon. Although multispecies cover cropping exhibited a positive effect on yield and some soil properties after 3 yr, we plan to continue collecting multiple years of data from this field trial.