Forms of soluble aluminium in acidic topsoils estimated by ion chromatography and 8-hydroxyquinoline and their correlation with growth of subterranean clover

Labile Al in the soil solution measured by 8-hydroxyquinoline (Al_HQ) was a better predictor of plant growth than trivalent Al (Al_IC³⁺) measured by ion chromatography (IC). HQ reacted with some organic Al complexes which did not separate during chromatography. In the presence of oxalic acid, Al_HQ was greater than Al_IC³⁺, which was the same as the greater than Al³⁺ (Al³⁺_Calc), whereas in the presence of citric acid, Al_HQ was greater than Al_IC³⁺, and both were greater than Al⁺³_Calc, In extracts of soils that had been acidified, Al³⁺_IC was less than Al_HQ, which was similar to Al³⁺_Calc, when it was assumed that the only complexing ligands were OH^? and F^?. The proportion of Al³⁺_IC in the soil solutions decreased more than Al_HQ as the pH increased. Organic ligands appeared to form complexes with Al at the expense of AIF complexes. Forms of Al detected by IC differed in CaCl₂ extracts and soil solutions. Al_HQ in the CaCl₂ extracts and soil solution were closely correlated, although the proportion of Al_HQ was higher in the CaCl₂ extracts. And soil solutions. Al_HQ in the CaCl₂ extracts and soil solution were closely correlated, although the proportion of Al_HQ was higher in the CaCl₂ extracts.