Jenkinson and Rayner (1977) developed a model to simulate the behavior of soil organic matter that was divided into five fractions. These fractions consisted of decomposable plant material (DPM), resistant plant material (RPM), biomass (BIO), humified organic matter (HUM) and inert organic matter (IOM). The model assumes that each fraction contains a single species that undergoes biological decomposition by the first-order process. On a monthly basis, the addition of plant carbon from crop residues is represented by the DPM and RPM fractions. In the model, the organic carbon inputs are assumed to enter the DPM or the RPM pools, which decompose forming CO2, microbial biomass, and humified organic matter. It is assumed that, for all soils, the ratio of microbial biomass to humified organic matter remains the same during biological activity. In the model, decomposition of humified organic matter by biological activity results in CO2, microbial biomass, and residual humified matter.The inert component does not undergo any transformation during biological activity.
(from: Donigan, A.S. et al. 1994 : Assessment of alternative management practices and policies affecting soil carbon
in agroecosystems of the Central United States. P.32.)
The model has been validated on Rothamsted soils for organic carbon content and total N content in the top 23 cm of soil. Good correlation between observed data and simulated results is reported. The current model (Jenkinson, 1990) was also validated for both organic carbon and microbial biomass contents, and simulated and observed results were in good agreement.