Effect of clay mineral content on soil acidification [antikvár]

EFFECT OF CLAY MINERAL CONTENT ON SOIL ACIDIFICATION P. Stefanovits University of Agricultural Sciences, Gödöllő, Hungary Soil acidification is a canmon process in non-calcareous soils. Its reasons however are still rnuch discussed, like the question of whether acidic deposition or iirproper fertilization has the greater effect on the soil acidification process. In an attempt to answer this question we would like to present our measurements which were repeated after 30 years /in the same places/. Among the data set out in Figure 1 special attention is invited to the results of those measurements which were taken in an oak-forest and in a nearby arable land situated at a distance of about 100 m from each other /STEFANOVITS, 1986/. Since the soil of the forest has never been fertilized, here any lowering of the pH can only be the consequence of acidic deposition. In the arable field however both acidic deposition and the acidifying effect of fertilizers should be taken into account. As from the data we could see that the extent of acidification was greater in the forest, we came to the conclusion that the effects of acidic deposition and fertilization in the ploughland did not add up. In spite of the buffering effect of cultivated plants the acidifying effect of fertilizers cannot be neglected but its value could not be established through field exper imént s. To clear this problem model experiments were carried out in laboratory. During the first experiment soil was mixed with salt solution to simulate freshly fertilized land. After this the soil mash was dried and the pH value, hydrolytic acidity and EDTA-soluble aluminium content were determined as the indicators of acidification. The amounts of sorbed and desorbable nutrition elements were determined, too. Eight soil samples were collected to represent the characteristic territories in the map of clay mineral associations of soils in Hungary /STEFANOVITS and DOMBÓVÁRI, 1985/ /Figure 2/. During the next experiment the number of soil sairples with different clay mineral contents was 35. The samples were saturated with KCl and NH4CI, then the amount of nutritive ions fixed on free surfaces and in the spaces between layers was determined. The results of experiments are shown in Table 1 and Figure 3.