Geochemistry of iron in soils of Vojvodina, Sumadija and Northern Pomoravlje
Iron is one of the most common elements in the Earth's crust and it is fourth on the list of abundance after oxygen, silicon and aluminum. It plays an important role in the biosphere. In plants it is necessary for the formation of chlorophyll, while in animals it acts in transferring oxygen from air or water to animal tissue. During a large-scale sample collection a regular orthogonal 10x10 km grid has been used to avoid bias in site location. From the set of about 3000 samples from Vojvodina, Sumadija and Northern Pomoravlje, a selection of samples (from the arable layer 0-25 cm) has been taken to represent the most important soil types. Total iron content has been determined by the atomic absorption spectrophotometric method (AAS). The soil samples have also been assayed for metal on a phase-specific basis following procedures according to the EC protocol Spatial distribution of iron content over the investigated area has been presented in a pedogeochemical map. The presented results have shown a wide range of iron contents, from 0.73 to 10.86% Fe. Statistical analysis of the results obtained from 103 samples has shown an average value of 4.06% Fe with the standard deviation of 1.682 and the coefficient of variation of 41.49%. Iron contents lower than 2.10% have been found in 4.32% of the samples, medium and average values (2.10-4.97% Fe) have been found in 55% of the samples, values higher then the average have been found in 26.3% of the samples and the contents higher than 7.86% have been found in 13.96% of the samples. Arenosols and rigosols developed on aeolian sands have shown the lowest levels of total iron, from 0.73 to 1.82% Fe. On the other side ranker developed on serpentinite has shown maximum contents, between 8.53 and 10.86% Fe. Soils developed either on loess or tertiary clay parent rocks (halomorphic soils, some marshy humogleys and vertisols) have shown a wider range of results (1.33-4.65% Fe) with a shift of results towards average values. The majority of the investigated soils that have fallen within the group between 3.00 and 4.96% Fe were represented by pseudogley, eugley luvisol, fluvisol, eutric cambisol, ranker and rendzina. Semigley and chernozem have shown a wider range of distribution of results, from 2.18 to 7.72% Fe.Generally, the analyzed soils have shown lower average results compared with the available literature data. Chemical speciation has shown that an average iron content of 84.24%, with the range from 70 to 92%, was primarily associated with residual forms bound to the silicate lithogenic fraction. An average of 12.69%, with the range from 6 to 26%, has been found as Fe-Mn-oxide/hydroxide fraction. Organic-matter-bound iron (1-9%) and exchangeable and carbonate-bound iron (0.09-1.92%) have been present to a lesser extent.