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The Influence of Anions on Potassium Quantity‐Intensity Relationships
Author(s) -
Evangelou V. P.
Publication year - 1986
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1986.03615995005000050018x
Subject(s) - loam , chemistry , potassium , organic matter , soil water , silt , ion , analytical chemistry (journal) , mineralogy , environmental chemistry , soil science , geology , paleontology , organic chemistry
Quantity‐intensity ( Q/I ) relationships for potassium (K + ) of soils sampled from three Maury silt loam sites (fine‐silty, mixed, mesic, Typic Paleudalfs) representing different crop management practices were investigated in 10 −2 mol c L ‐ each of Cl ‐ or SO 2‐ 4 solutions. Soil samples from the three sites were (i) low in exchangeable K + and organic matter (LK‐LOM), (ii) high in exchangeable K + with low organic matter (HK‐LOM), and (iii) high in exchangeable K + with relatively high organic matter (HK‐HOM). A theoretical evaluation of K + Q/I plots in Cl ‐ or SO 2‐ 4 solutions employing the Gapon equation, revealed that the potential buffering capacity for K + (APBC k ), the labile K + (AExK 0 ) and equilibrium activity ratio for K + (AR K0 ) based on single ion activities and ion pairs of CaSO 0 4 , KSO ‐ 4 and CaCl + were independent of the type of solution anion. When considering total dissolved concentration of K + and Ca 2+ , the potential buffering capacity for K + (CPBC K ) and equilibrium concentration ratio for K + (CR K0 ) differed between Cl ‐ and SO 2‐ 4 solutions. The labile K + (CExK 0 ) remained the same. These results were due to the differences in ion pairing abilities between Cl ‐ and SO 2‐ 4 with K + and Ca 2+ . The influences of the ion pairs are minimized at decreasing CR K0 values. The experimental data describing Q/I relationships for K + for the three soil samples were not in full agreement with the theoretical observations. The data showed that the type of anion (Cl ‐ or SO 2‐ 4 ) had an effect on the CR K0 and CExK 0 , but the values were not significantly different except for the HK‐HOM sample. The experimental data for the soil samples HK‐LOM and HK‐HOM indicated agreement to some extent with the theoretical evaluation. For the same CR K values in the Cl ‐ or SO 2‐ 4 anions, a greater change in exchangeable K + (ΔExK) was observed in the SO 2‐ 4 system than in the Cl ‐ system. However, for these two soil samples (HK‐LOM and HK‐HOM) when the Q/I plots were constructed considering single ion activities, differences remained in the Q/I plot components AR K0 and AExK 0 between the two anionic systems. For the LK‐LOM soil sample the Q/I plots appeared to be nearly identical for the Cl ‐ and SO 2‐ 4 systems in terms of total cation solution concentrations and/or solution single ion activities. This agreed with the theoretical evaluation.