NORMALIZED STABILITY INDEX AND MEAN WEIGHT DIAMETER IN A COMBINED NITROGEN FERTILIZATION X IRRIGATION EXPERIMENT ON HUNGARIAN CHERNOZEM SOIL Andrea HUISZ,Tibor TÓTH, Tamás NÉMETH Abstract: Soil management and tillage practices could be remarkable stress factors on structure of soil which might be ruined and therefore cause the reduction of crop yields. The effect of irrigation and fertilizers on soil structure may be diverse and often contradictory. In contrary to the often proved soil structure disrupting effect of irrigation, in our experiment, as the result of irrigation, increased aggregate water-stability was observed. In unfavorable conditions, or in large accumulation, ammonium fertilizers may cause the disruption of soil structural units, therefore decline of soil structure as it was observed in our experiment. These results were compared with the Normalized Stability Index and Mean Weight Diameter of which the second one showed significant differences among the treatments.