The Effect of Acidic Amendments on the Behaviors of Potassium in Calcareous Soils

Abstract

Carbonates, particularly CaCO3, in calcareous soils with a high soil pH, result in a K/Ca value that is very small and the plants cannot efficiently use the potassium (K). One way to improve calcareous soil is to lower its pH value by applying acidic amendments. However, research on the effect of the acidic amendments on the behaviors of K in calcareous soils is limited and further assessments are required. The objectives of this study were to investigate the behavior of K when sulfur(S) and aluminum sulfate[Al2(SO4)3•14H2O] were applied to reduce the pH of calcareous soils. Five calcareous soils with different CaCO3 levels were examined. Incubation was performed while different amounts of S and Al2(SO4)3•14H2O were applied to the soil until the soil pH was lowered to 7.0 and 6.5 under the condition of 25℃ and -33kPa water potential. The pH values, and the concentrations of different forms of K in the soils were measured throughout the incubation period. The pH values, various concentrations of forms of Ca, Mg and K as well as the quantity/intensity (Q/I) relationships of K were measured after the incubation. The result of applying acidic amendments to five types of soils indicated that more solution K was released than S when applying Al2(SO4)3•14H2O during the initial stage. A rich concentration of solution K was retained in these five types of soils, even after being incubated for eight weeks. The addition of acid amendments promoted the release of non-exchangeable K in slate calcareous alluvial soils. Nevertheless, a fixation did occur for soils with a lower non-exchangeable K content and that experience severe weathering such as the Yuanlin soil. Acidification of calcareous soil lowered the AR(subscript K)° to be as low as 1×10^(-3)(mol/L)(superscript 1/2) or less. This result did not improve the soil supply of K to the plants over the short term. However, the high potential buffering capacity of K (PBC(subscript K)) indicated that the frequency of using K fertilizer should be reduced, and a large amount of K fertilizer should be needed.