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Selectivities of Potassium-Calcium and Potassium-Lead Exchange in Two Tropical Soils

^a Earth and Soil Sciences Dep., Cal Poly State Univ., San Luis Obispo, CA 93407
^b Dep. of Soil and Water Science, Univ. of Florida, Gainesville, FL 32611-0290

View larger version (22K): [in a new window]   Fig. 1. Gaines-Thomas selectivity coefficients (KGT) vs. equivalent fractions of Ca2+ on the exchanger (ECa) in the (a) Oxisol and (b) Ultisol or Pb2+ on the exchanger (EPb) in the (c) Oxisol and (d) Ultisol.

View larger version (26K): [in a new window]   Fig. 2. Exchange isotherms for Pb2+ or Ca2+ replacing K+ on exchange sites as well as heterovalent exchange nonpreference isotherm on the Oxisol and Ultisol soils. ECa and EPb = equivalent fractions of either Ca2+ or Pb2+ on the exchanger and E'Ca and E'Pb = equivalent fractions of either Ca2+ or Pb2+ in the equilibrium solution.

View larger version (157K): [in a new window]   Fig. 3. SEM-EDX elemental dot maps of (a) Oxisol and (b) Ultisol soil samples. Light areas of the dot maps indicate elevated concentrations of a particular element. The first letter/s in the upper right-hand corner of each box represent/s the particular element of concern, Ka = K- excitation energy; Ma1 = M- 1 excitation energy, and the numbers correspond to the relative elemental intensities in counts per second.