Abstract: This paper exposes an extension of the simplest mathematical model of soil organic matter decomposition. The equation of this model is very common in the literature, for example, Davidescu and Davidescu (1981), or Willigen et al. (2008), considering some changes in a single model-components, such as Schnitzer and Khan (1978). The main idea is that the development of natural processes, is directly influenced only by the natural parameters (temperature, humidity, etc.), and only indirectly by the temporal parameter. The model proposed in this paper express this idea. Time dependence of the concentration of organic matter in soil is due only by the time dependent describing of the natural parameters evolution. This time dependence facilitates on human observer the understanding and communication. The prognosis of the concentration of organic matter in soil and the evaluating of the fertilizer management are application of the model.