Soil Solutions of Organic Horizons in Some Acid Forest Soils

The equilibrium soil solution (ESS) of thirteen O horizons from six Dystrochrepts and one Spodosol on granitic, phyllitic and basaltic solifluction material in the Fichtelgebirge mountain range was analyzed for organic carbon (DOC), optical density at 465 nm (OD465), base neutralization capacity (BNC), and various cations. The pH of the ESS was from 2.95 to 4.0 and from 4.1 to 4.2 in the phyllitic and granitic soils and in the basaltic soils, respectively. The concentration (mmol/L) of Ca and K ranged between 0.2 and 0.9 but was only < 0.18 for Mg, corresponding to the Mg deficiency in spruce identified in this area. Al (0.07–0.56 mmol/L) was partitioned into “labile” and “non-labile” (complexed) fractions on the basis of polarographic measurements and a fast reaction with hydroxyquinoline (HQ). The polarograms indicated one hundred percent Al complexation in 9 out of 11 ESSs whereas an average of only 63% was nonreactive with HQ. Complexed Al was correlated with DOC (R2 = 0.47*), OD465 (0.63**) and the corrected BNC for pH 7 (0.82***). By adding small increments of Al to the 9 “non-Al-saturated” ESSs, an Al complexing capacity was polarographically determined. It ranged between 0.3 and 2.8 mmol/L and was saturated in the natural state to more than 90% in 7 out of the 9 ESSs. The average composition of the Al-organic complex in M NH4Cl extracts (pH 2.7–3.8) as deduced from OH consumption was [Al Lc.66]2.34+ (L = monovalent ligand). Gleichgewichtsbodenlosungen von O-Horizonten einiger saurer Waldboden.