EFFECTS OF LIMING ON SOIL PROPERTIES AND P SOLUBILITY IN SOME SPANISHANDOSOLS

The effect of application of liming material (CaCO3 or CaSiO3) and pho sphate, on pH, exchangeable Al, effective cation exchange capacity (EC EC) and P solubility is studied in several variable-charge soils of vo lcanic origin from Canary Island (Spain). The amendments were added to replace 1.5 X or 2.5 X exchangeable Al, and P was applied at rates to provide equilibrium solution concentrations of 1 mg l(-1). Incubation of the samples with P, had very little or no effect on pH and on the exchangeable Al content of the soils. When P and amendments were combi ned, exchangeable Al levels declined with no concomitant effect on pH. Phosphate application alone produced a small increase in the effectiv e cation exchange capacity (ranging from 0.2 to 16.1 mmol(c) kg(-1)). This effect being much more marked when liming materials were previous ly added. Prior addition of CaCO3 did not produce any effect on soluti on P, irrespective of the exchangeable Al content of the soils. On the contrary, in some of the soils CaSiO3 treatment increased P concentra tion in solution.