The influence of surface incorporated lime and gypsiferous by-products on surface and subsurface soil acidity. I. Soil solution chemistry

Lime, fluidised bed boiler ash (FBA), and flue gas desulfurisation gypsum ( FGDG) were incorporated in the top 50 mm of repacked columns of either an A llophanic (the Patua sand loam) or an Ultic (the Kaawa clay loam) soil, at rates containing calcium equivalent to 5000 kg/ha of CaCO3. Each column was leached with 400 mm of water. After leaching, the columns were sliced into sections for chemical analysis. In the columns of the variable-charged, al lophanic Patua soil, topsoil-incorporated FBA ameliorated top and subsurfac e soil acidity through liming and the `self-liming effect' induced by sulfa te sorption, respectively. The soil solution pH of the top and subsurface l ayers of the Patua soil were raised to pH 6.40 and 5.35, respectively, by t he FBA treatment, compared with pH 4.80 and 4.65, respectively, in the cont rol treatment. Consequently, phytotoxic labile monomeric aluminium (Al) con centration in the soil solution of the FBA treatment was reduced to <0.1 mu M Al, compared with 8-64 mu M Al in the untreated control. FGDG had a simi lar `self-liming effect' on subsurface of the Patua soil, but not the topso il. Whereas FBA raised the pH of the Kaawa topsoil, no `self-liming effect' of subsurface soil by sulfate sorption was observed on the Kaawa subsurfac e soil, which is dominated by permanently charged clay minerals. Applicatio n of FBA and FGDG to both soils, however, caused significant leaching of na tive soil Mg2+ and K+. These nutrients were displaced from the exchange sit es by the relatively high concentration of Ca2+ released from dissolution o f gypsum.