The chemical composition of forest soils and their degree of acidity in Central Europe

Abstract

We conducted an extensive screening of forest soils in the whole area of the Czech Republic to determine their degree of acidification and potential degradation. Soils were sampled at 480 forest sites (in a 7 × 7 km grid covering the entire Czech Republic) from the upper 30-cm layer and included both organic and mineral horizons. Based on values of water extractable pH (pHH2O), cation exchange capacity (CEC) and base saturation (BS), soils were divided into three categories by their degree of acidity, i.e., non-or-low-acidic (NLA; pHH2O ≥ 4.2, CEC ≥ 150 meq kg−1, BS ≥ 15%), moderately acidic (MA; at least one parameter is below the limits for the NLA category), and strongly acidic (SA; all three parameters are below the limits for the NLA category). Only 11% of sampled soils were classified in the NLA category, while 58% and 31% belonged to the MA and SA category, respectively. The SA soils had median values of pHH2O, CEC, and BS of 3.9, 102 meq kg−1, and 10.2%, respectively, and their molar ratios between exchangeable concentrations of base cations to aluminum (BCex/Alex) were <0.6, indicating a high likelihood of adverse Al effects on plant growth. Moreover, the SA soils exhibited lowest ratios between extractable nutrients (base cations and phosphorus) and dissolved N (DN), indicating other than N limitation of plant growth at these sites, and elevated risks of reactive N leaching. In contrast, the NLA soils had median values of pHH2O, CEC, BS and BCex/Alex of 5.4, 199 meq kg−1, 95%, and 0.7 respectively. For these soils, neither adverse effects of Al nor elevated N losses are likely.