The dynamic of soil organic matter (SOM) can be studied under arable land circumstances mostly in long-term field experiments (LTE) where the various processes are strongly influenced by the environment and the changes are realised in years and decades. The topic in the title was investigated in a two factorial long-term field experiment in Keszthely (Pannon University Georgikon Faculty, South-West Hungary) with a three-crop rotation: maize, winter wheat, winter barley in the 1984–2013 period. The LTEs are carried out with the cooperation of IOSDV/ILTE experimental series.

The increasing rates of N fertiliser significantly increased the yield of maize on the basis of N0 treatments, the maximum yield were obtained at the 210–280 kg ha-1 N nutrient level. The positive effect of organic manure (FYM) in the average of N treatments were 7% and in the case of N0 fertiliser treatments 20% were measured. The residue management (straw+green manure, ST) produced 3% and 10% yield increase, respectively. The proper nutrient supply, mostly the good SOM status of soil decreased the climate effects and the annual changing of maize yield considerably. In the treatments of without organic manures the OM content of soil (10–30 cm) decreased significantly during the three decades, 0.720 g kg-1 at the same time in the treatments of FYM+NPK the humus content of soil increased to a certain extent, but it has not exceeded the significant differences. At the straw+green manure (oil radish) management the SOM content of soil did not change and remained almost the same level as had been at the

starting status in 1984.

Based on the many years of research work it is concluded that the decrease of OM content in the soil and the degradation of soil can be stopped even in intensive crop production, furthermore, the soil fertility and the productivity of agro-ecological region can be preserved in the long run as well.

Keywords: long-term field experiments, SOM status and dynamic, FYM, residue, cover crop, maize N response