Equilibrium solution composition and exchange properties of disturbed and undisturbed soil samples from an acid forest soil.

摘要

Microscalic heterogeneity of soil chemical properties caused by soil structure has been reported for several soils. Exchange properties and soil solution composition of disturbed and undisturbed samples of an acid forest soil lacking visible structure were investigated. Cation concentrations in the soil solution resulting from two extraction procedures and two analytical methods were compared. The effective cation exchange capacity (CECe) of the undisturbed sample represented 56-69% of the bulk soil CECe. Base saturation of undisturbed samples equalled that of disturbed samples for EA, Bhs, and Bsh horizons, and was higher for the Bw horizon. Contradicting the results of other authors, soil pore solution obtained by percolating soil cores under conditions of low water tension offered more favourable conditions for plant roots when compared with the equilibrium soil solution of the bulk soil sample in all except the Bsh horizon. Ca2+/Al3+ molar ratios were higher and fractions of H+ + Al3+ on total cationic charge were lower in the soil pore solution. These results were obtained employing soil:solution ratios of about 1:0.5 during the extraction of soil pore solution, and by determination of free cations. Other authors used a water extraction with soil:solution ratios up to 1:2 and took total metal for ion concentrations. The combination of the latter extraction and analytical method in this study, too, led to unfavourable Ca2+/Al3+ ratios and high fractions of H+ + Al3+. The choice of analytical and extraction method are thus decisive for the valuation of the soil solution composition in view of plant nutrition.