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determination of soil pH ( HRN ISO 10390:2005), determination of organic carbon and total nitrogen after dry combustion (HRN ISO 10694:2004; HRN ISO 13878:2004), mineral content of the soil (XRD) by X-ray diffraction method and content of the elements Ca, Mg, K and Na after extraction with aqua regia (HRN ISO 11466:2004) were determined in the samples taken from genetic horizons in the pedological profiles.
For statistical purposes, the lithological bedrock was divided into seven characteristic lithological units, which were used by geologists Halamić et al. (2001) in their study of stream sediments on Medvednica. Lithological unit LIT1 is made up of parametamorphic rocks, Lithological unit LIT2 is composed of orthometamorphic rocks, Lithological unit LIT3 consists of igneous rocks, Lithological unit LIT4 is formed of Mesozoic clastic rocks, Lithological unit LIT5 is comprised of Tertiary clastic rocks, Lithological unit LIT6 consists of Mesozoic carbonate rocks and Lithological unit LIT7 is made up of Tertiary carbonate rocks.
Statistical analysis was performed in Statistica 7 software package. Descriptive statistics was made for all the analyzed variables: number of samples, minimum, lower quartile, median, upper quartile, maximum, mean, standard deviation, coefficient of variation, standard error of mean and skewness. In order to eliminate the effect of outliers and extreme values, the median was taken as the mean value. Mutual differences between the analyzed values per lithological bedrock were tested using the Kruskal-Wallis non-parametric test. Type 1 (a) error of 5% was considered statistically significant.
The highest pH value was recorded for the topsoil layer in LIT6 and LIT7. LIT6 has statistically significantly higher pH value than LIT1, LIT2, LIT3, LIT4 and LIT5, while LIT7 has statistically significantly higher pH value than LIT2, LIT4 and LIT5. Statistically significant positive correlation between pH values and Ca concentrations were found in all lithological units. Statistically significant positive correlation between pH values and Mg was also established for LIT1 and LIT5, and between pH values and K for LIT2 and LIT4. In terms of Mg concentration, two groups were clearly identified: one consisting of LIT4, LIT5 and LIT7 with lower concentration, and the other comprising LIT2, LIT3 and LIT6 with higher concentration, while LIT1 is between the two groups.
The following soil types were determined in the opened pedological profiles: dystric cambisol, eutric cambisol, calcocambisol, pseudogley on slope, colluvium and luvisol (50% – 18% – 14% – 11% – 4% – 4%). In general, the humus-accumulative horizon on Mt Medvednica is shallow – the median is 3.3 cm, and the mean is 3.9 cm. The next horizon, which is usually cambic, is 31 cm and 33 dm thick. The range of organic C content in the humus accumulative horizon ranges from medium humic to very humic soil. The soil is rich to very rich in total nitrogen, and the C/N ratio is favourable. The soil texture is most frequently silty loam, while on the carbonate bedrock it is of somewhat heavier – silty clay loam. The content of individual minerals, and of Ca, Mg, K and Na in the humus-accumulative and mineral horizon is more or less equal, while the correlation between the horizons is statistically significant (p<0,01). For quartz it is r = 0.81, muscovite/illite r = 0,68, chlorite r = 0,76, feldspate r = 0,69, Ca r = 0,85, Mg r = 0,88, K r = 0,82 and Na r = 0,52. The highest pH values and Ca, Mg, K and Na concentrations in beech-fir forests were recorded in the surface soil layer at a depth of 5 cm in LIT3. A statistically significant difference in Ca concentration was found between LIT3 and LIT2 and in Na concentration between LIT3 and LIT1.
The obtained Ca and Mg concentrations in the topsoil of Medvednica Nature Park are in accordance with the values recorded in Central Croatia by Halamić and Milko during their work on the Geochemical Atlas of the Republic of Croatia (2009). The data for all the obtained elements concord with the results obtained from a study of the condition of forest soils in Europe (Vanmechelen et al., 1997). The relief (elevation, inclination, exposition, curvature) do not affect the spatial distribution of Ca, Mg and Na in the topsoil to a depth of 5 cm. Although there is a statistically significant correlation between elevation and Mg concentration, and slope and Mg concentration, this correlation is actually conditioned by the lithological bedrock. Beech-fir stands developed on the soils above basic igneous rocks are characterized by a higher Ca, Mg, K and Na content, and consequently higher pH values. As a result, a higher number of neutrophilic species can be expected in these forests.
Key words: alkali earth and alkali metals, Medvednica Mount, forest soil