POTASSIUM-AMMONIUM-CALCIUM QUANTITY/INTENSITY STUDIES IN THE BINARY AND TERNARY MODES IN TWO SOILS OF MICACEOUS MINERALOGY OF NORTHERN GREECE

Abstract

Binary systems, such as K - Ca or NH₄ - Ca pairs, are used commonly in traditional Quantity/Intensity studies, and it is assumed that the results obtained can be extrapolated to ternary systems. It is also believed that K and NH₄ behave analogously with respect to micaceous clay minerals. The existing data on the subject of ternary systems, however, and on the interaction between K and NH₄ in soils do not provide enough evidence that ternary exchange reactions, K - Ca - NH₄, in soils can be predicted from binary exchange data. In this study, the Q/I relationships of K-Ca in the presence and absence of NH₄ and of NH₄-Ca in the presence and absence of K were investigated in two soils of micaceous clay mineralogy: an acidic Alfisol (Ultic Haploxeralf) and a calcareous Entisol (Typic Xerorthent). In both soils, as expected, the addition of NH₄ to the K-Ca system decreased the potential buffering capacity for potassium (PBC_K), and the addition of K to the NH₄-Ca system decreased the PBC_NH4. The data also revealed that in these two solid, K and NH₄ at low exchangeable loads did not behave as the true exchange analogs one commonly expects. Ammonium was more capable of displacing K from the solid surfaces than K was of displacing NH₄. This indicates that K-NH₄ interactions are complex. In certain soils, addition of NH₄ fertilizers might increase potassium availability, whereas in others, the opposite can be true.