This paper describes the production planning model of the fertilizer sector of a Finnish industrial company, Kemira Oy. The model was tested by us using the computer of the Technical Research Centre of Finland (VTT). The test results are given and the nature, benefits and limitations of doing experimental research with an implemented model are described. By means of the model, the impact on the activities of the fertilizer sector of changing the supply of raw materials, the plants capacity, as well as the transportation routes of raw materials and products, was studied. The results provide a basis for determining eight ‘systems characteristics’ of the fertilizer sector.