Estimating Net Nitrogen Mineralization from Carbon Dioxide Evolution

Abstract

Abstract The ability to estimate net N mineralization from C decomposition data has the potential to improve our understanding of N dynamics in soil systems. It was the objective of this study to study this relationship using substrates with varying decomposition rates and C/N ratios. Five substrates including sewage sludge, alfalfa ( Medicago sativa L.), clover ( Trifolium sp.), bermudagrass [ Cynodon dactylon (L.) Pers.] and ryegrass ( Lolium multiflorum Lam.) were incubated in Crowley silt loam (Typic Albaqualfs) or Captina silt loam (Typic Fragiudults) soil at known soil temperatures and moistures. Concurrent CO 2 evolution and soil inorganic N concentrations were measured periodically. A significant linear relationship between N mineralization and CO 2 evolution was found experimentally for each substrate. A computer simulation model was developed which used first order kinetics for conversion of substrate C to CO 2 . Substrate C mineralization rate constants, substrate C/N ratios and microbial efficiency were primary inputs, while substrate, biomass, and soil organic matter were the major compartments of the model. Microbial efficiency was defined for any C pool undergoing decomposition as the ratio of assimilated C to assimilated C plus dissimilated C. An important feature of the approach was the introduction of a fraction with a C/N ratio of protein that decomposed very rapidly for those substrates where initial N mineralization was large while CO 2 evolution was small. Model predictions of both CO 2 evolution and net N mineralization were in good agreement with experimental results.