Soil Saturation Extract Composition and Sulfate Solubility in a Tropical Semiarid Soil
Soil solution is the major source of plant nutrients, nutrient cycling in ecosystems, and pollutant transformation and transport in soil. I examined the composition of soil saturation extract of a cultivated and an uncultivated savanna Alfisol to determine the relations of Ca2+, Mg2+, and K+ concentrations in soil solution with exchangeable Ca, Mg, and K; and to determine the solubility relations of SO4 for which there is little information in savanna soils. The soil saturation extract had ionic strength (I) below 0.001 except for one field under intensive fertilization with NPK fertilizer and farmyard manure (FYM) whose ionic strength was between 0.001 and 0.002 at a depth below 40 cm due to leaching. The Ca2+, Mg2+, and K+ in the soil saturation extract correlated weakly with exchangeable Ca, Mg, and K respectively, but K+ intensity was fairly well predicted by percentage of K saturation of cation-exchange capacity (CEC), whereas the intensities of Ca2+, Mg2+, and SO4 2− in soil solution were best predicted by electrolytic conductivity of the saturation extract. The K activity ratios in solution defined as aK/(aCa + aMg)1/2 were <0.01 in the cultivated soil, suggesting a preponderance of K adsorbed to edge rather than planar sites. The Ca2+ activity ratios defined as aCa/[∑aCations] were <0.15 for the cultivated soil, indicating possible Ca deficiency. The SO2− 4 activities in solution were in apparent equilibrium with basaluminite in the cultivated fields, whereas in the uncultivated field, SO2− 4 activities were in apparent equilibrium with alunite.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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