Model for decomposition of organic material by microorganisms

A theoretical model which gives the rate of microbial decomposition of organic material (plant or animal residues, or soil organic matter) is presented. Explicit equations for the rate of decomposition, mineralizations and immobilization are given. The main assumption of the model is that the rate of decomposition of any substrate is proportional to the growth rate of its decomposers. The main results of the model are: 1. Addition of extra nitrogen to materials poor in nitrogen increase their rate of decomposition; 2. Addition of extra nitrogen to a substrate whose initial carbon/nitrogen ratio is above a critical ratio (20-30) causes a decrease in the substrate's carbon/nitrogen ratio during its decomposition; 3. If the initial carbon/nitrogen ratio is below the critical one, no change in the substrate's ratio will occur with time; 4. Net mineralization of organic-nitrogen occurs when the substrate being decomposed has an initial carbon/nitrogen ratio which is below the critical one; 5. Addition of ammonium to such a substrate (point 4) will increase the rate of organic-nitrogen mineralization but not necessarily the rate of net mineralization. All the model results are analytical and independent of the values for the various parameters. Nevertheless the application of the model to real field conditions is discussed while presenting a numerical example.