Soil organic matter (SOM) is one of the most influential properties regarding soil fertility. Various crop species and varieties, as well as plant nutrition application may have an impact on the amount of soil organic matter. In a small plot field experiments the most characteristic agronomic impacts (biological bases, production sites, plant nutrition and crop year effects) influencing the efficiency of carbon sequestration of two major crop plants: -wheat Triticum aestivum and maize Zea mays have been studied. The aim of the research was to observe, identify and quantify agronomic impacts and their interactions that may have an influence on organic matter formation and so on carbon sequestration. Crop variety and plant nutrition proved to be the most important factors influencing organic matter production. Interactions have been found between crop plant genotypes and N levels applied.