Effects of incubation time and filtration technique on soil solution composition with particular reference to inorganic and organically complexed Al

Abstract

Soil solutions were extracted from surface and subsoil samples of highly weathered soils in the field moist state and from air-dry samples which had been re-wet and incubated at 28°C for 1 to 64 days. Soil solutions were analysed following filtration through 0.22 pm and 0-025 µm pore-diameter hembranes. Selected samples were also incubated following sterilization by gamma irradiation (50 kGy) to investigate the effects of microorganisims on soil solution C dynamics. Ultra-filtration did not affect the concentration of the major cations or anions but significantly reduced Al, Fe, Mn, Si and organic C concentration in some surface soil solutions extracted from field-moist samples and from re-wet air-dry samples after short incubation periods. The organically-complexed Al concentration in soil solution was significantly increased by air-drying and re-wetting soil; the organic Al concentration decreased with increased time of incubation to levels comparable with that present in field-moist samples. Inorganic monomeric Al reached a stable concentration, comparable with that in field moist samples, when air-dry soils were re-wet and incubated for 1 day. While gamma irradiation effectively sterilized the soil and stabilized the concentration of Al and organic C in solution, the magnitude of the changes in soil solution composition observed as a result of irradiation diminish the value of this finding.