ANALYTICAL MODEL OF THE DECOMPOSITION OF SOIL ORGANIC-MATTER

An intermediate resolution model of the decomposition of soil organic matter is developed from a comprehensive study of published experimental work. The many organic and inorganic forms of soil N, P, and K are mathematically treated, together with the various transformations between forms. Most of the transformations are moderated by microbes, and the dynamics of the microorganisms are explicitly represented. A simulation is made of a general heterotrophic population using organic C and N for energy, as well as nitrifiers which oxidize nitrogenous compounds chemotrophically. Such explicit treatment of microbe dynamics permits among other things the study of microbe immobilization of important plant nutrients. In addition to the simulation of biological aspects of decomposition, the model treats the physicochemical processes of precipitation, fertilizer and native mineral inputs, leaching loss, sorption of organic and inorganic ions on soil colloids, condensation between organic N and aromatic compounds, and exchange reactions. Model parameters are dealt with in detail in order to base them as firmly as possible on experimental information. The process rates include functional dependence on soil temperature and moisture. For clarity of presentation, the model is divided into four submodels, one each for N, P, and K, and the C energy substrate. The total model is coupled with a previous plant growth model, and thereby simulates complete element cycles within the plant-soil system. © 1979.