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| Vogt, R; Matschonat, G: Patterns of soil solution composition in acid forest soils: differences between undisturbed and bulk samples, Z. Pflanzenernährung Bodenkunde, 160, 549-554 (1997) | |
Abstract:
In acid forest soils pores draining under conditions of low water tension
contain a solution usually differing in composition from the equilibrium
solution of the bulk soil. For tree nutrition, the former was described
as comparable to the bulk soil solution or less favourable. Our
recent work on solution quality contradicted the universal validity of
these findings. It turned out that the methods usually recommended
tend to consistently reproduce the pattern of more advanced acidification
of coarse pores. We applied our combination of methods to a
range of soils to find out whether our previous finding of more favourable
solution conditions in undisturbed soil samples as compared to
the bulk soil is common or rather an exception. Undisturbed cores and
bulk soil were sampled from four forested sites differing in pH and
base saturation. We used an iterative procedure to adjust the equilibrium
soil solution of disturbed soil and a water extraction with a
soil:solution ratio of 1:2. To extract solution from undisturbed soil
cores only small volumes of water were added, and we distinguished
analytically between total (by ICP) and ionic (by CE) concentrations
of cations. We calculated Ca/AI molar ratios and the fraction of (AI’+ +
H+) on total cationic charge in solution as criteria for solution quality.
Whereas with total concentrations, there always appeared to be less
favourable conditions in the soil pore solution, free ionic concentrations
allowed a differentiation between the soils. In view of plant nutrition,
the quality of the soil solution from undisturbed samples was
better, equal to, or worse than that of the bulk soil, suggesting that
forest sites represent a continuum with respect to these chemical gradients.
Even in soils where gradients are not observed it is not necessary
to assume an equilibrium achieved by internal processes to exist
between coarse pores and the bulk soil. |
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