The results of twenty-year-long field, model, and pot experiments performed in Germany, Poland, Denmark, and Sweden testify that at least two fractions of soil organic matter (SOM) should be taken into consideration for the assessment of changes in SOM. The first is the inert part of SOM that depends on the clay content. The second is the transformed fraction that is influenced by soil management systems. The observed changes in the transformed fraction content are very slow and do not exceed 500 kg C_org/ha and 40 kg N_tot/ha per year even upon sudden changes in the fertilization system. The ecologically optimum amounts of the transformed SOM in chernozem are given for traditional cropping systems in Central Germany.