Factors Affecting Soil Acidity in Hungary

The Typic Haplustalfs soils (Karád and Oltárc) and the Typic Ustochrepts (Gödöllő) are developed on loess, and on aeolian sand parent material, under forest vegetation, resp. The Dystric Ustochrepts (Velem) soil formed on metamorphic schist parent material and had forest vegetation, while the Typic Medisaprists (Zalavár) soil developed on peat parent material and had marsh vegetation. Based on this study the spatial variability of surface pH samples indicate that the TIM sampling procedure should be improved. Ten to thirty samples must be collected at each site to be able to monitor changes of 0.2 pH units. If only one sample is taken at each site yearly, spatial difference in pH or other parameters are likely to obscure differences which may be occurring over time. The colloidal composition (organic matter and clay minerals), influenced by parent material, vegetation, and precipitation, showed a close relationship with the acidity factors, such as pH, HAC ₁ and EAC ₁ values. The pH values were the lowest in the Velem and Oltárc soils where the annual precipitation was the highest (750-800 mm), and in the Karád soil, where the annual precipitation was 650-700 mm. The Gödöllő soil had the highest pH values, probably due to the lowest amount of rainfall (550-600 mm) and the disturbance. The Zalavár soil had fairly high pH throughout the profile probably due to a fluctuating water table. The HAC ₁ and EAC ₁ values were the highest in the Velem soil when compared to the other mineral soils. The pH values were the lowest at this site. The HAC ₁ and EAC ₁ values were lower in the other three forest soils, at the Karád, Oltárc, and Gödöllő sites. The Zalavár soil had fairly high HAC ₁ values in the H3, H4 and H5 horizons, probably due to the very high OM content, which provided a lot of H ⁺ ions that can dissociate from the exchange sites. The E4/E6 ratios were closely related to the decomposition or humification rate in the upper and the subsurface horizons with accumulation of low molecular weight soluble fraction in the deeper horizon. The mineralogical analysis showed similar compositions for the soils developed on loess (Karád and Oltárc), or aeolian sand (Gödöllő), where the major minerals were vermiculite, mica, kaolinite, and chlorite. A different mineral composition (mica, vermiculite, clintonite, and kaolinite) was observed for the Velem site, where the parent material was metamorphic schist. The four mineral soils are forest soils, with a predominant downward water movement, thus with fairly intensive leaching process. However, there was a distinct difference among the soils formed on loess (Karád and Oltárc), or aeolian sand (Gödöllő), and the soil (Velem) developed on metamorphic schist parent material. The soils at the Karád, Oltárc, and the Gödöllő sites were less acidified, with higher pH, and lower HAC ₁ , and EAC ₁ values as compared to the Velem soil, even if the precipitation was very high. The calcareous loess parent material probably compensated for the higher precipitation and the resulting leaching process at the Karád and the Oltárc sites. The Gödöllő soil received a very low amount of precipitation, which resulted in a low degree of weathering, with higher pH, and lower HAC ₁ , and EAC ₁ values. However, the metamorphic schist parent material probably contributed to a lower pH and lower buffering of the developing soil. Based on the chemical and physical analyses, we concluded that among the soil forming factors, precipitation and parent material had the greatest influence on the acidity characteristics of the examined soils. The parent material influenced the mineralogy of the developing soil, which then influenced the pH, HAC ₁ , EAC ₁ , and CEC values of the soil. In order to substantiate these tendencies more samples from a wider array of geological regions are needed.