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At Putnok, in 1964 on acid clay illuviated brown forest soil, NPK plot trials were set up to evaluate the effect of nitrogen, phosphorus and potassium. In the trial the indicator plants were in succession Winter wheat, maize arid spring barley The yields of the indicator plants have been regularly measured; the authors reported several times about the effect of fertilization in this periodical Crop Production.

In this paper the authors evaluate the change in soil acidification. It was stated that on the control plots the acidification in considerable, the pH KCL value decreased by 0,37-0,55, while the y1 value increased by 4,7. The acidification measured on control plots may be attributed to the atmospherical acid effects, the global loading is increased by the local loading of the industrial area in Borsod. On the effect of fertilizer combinations with different proportions and compositions the further acidification (compared to control) was of a lesser degree, the pH value was between +0,12 and -0,43, the y1 between -1 and +10. The soil acidifying effect of the various fertilizer forms is different, the effect of calcium-ammonium-nitrate with nitrogen content was determined in these trials.

As it unlikely that the atmospherical - global and local - loading would fall to such an extent that the further acidification of our soils could be excluded, similarly it is not likely that the drastic decrease observed nowadays in the use of fertilizers will be long-lasting. The results of the tests prove unanimously, that the higher rate of acidifications is caused not by the agricultural production, but by the atmospherical sedimentation, therefore it should be expected that countering the damage should be the obligation of institutions causing the damage.

The rate of damage may be determined only by exact long-term trials, that is why it is indispensably necessary in the opinion of the authors to continue with the trials, especially on the highly exposes areas.