The effect of acid loads on the contents and stores of exchangeable cations and nonexchangeable acidity in forest podzolic soils

Acid loads equal to 1200 and 3600 mmol-equiv/m(2) reduce the pool of exchangeable Ca, Mg, and K in the organic horizons (L + F + H) by 570 and 820 mmol-equiv/m(2) Z Z, respectively. At the same time, the amount of these cations in the A1A2 and A2 horizons increases by 1200 and 1300 mmol-equiv/m(2), respectively. This is caused by the mobilization of Ca, Mg, and K from less soluble compounds of these elements upon acidification. In the case of a proton load equal to 3600 mmol-equiv/m(2), the rise in the reserves of nonexchangeable acidity within the L, F, H, A1A2, and A2 horizons is three times as high as the external acid load. This phenomenon may be caused by the additional release of protons with root exudates owing to a more intense uptake of base cations by the biota.