PHOSPHATE AVAILABILITY AND INORGANIC TRANSFORMATION IN AN ALUM SLUDGE-AFFECTED SOIL

Land application of alum sludge is a disposal alternative, A greenhous e experiment was conducted to determine (i) alum sludge effects on pho sphorus (P) availability and inorganic P forms, and (ii) the relations hip between inorganic P fractions and P availability. Alum sludge slur ry (0, 4.45, 8.9, and 17.8 g solid kg(-1) soil) was surface applied to wheat (Triticum aestivum L.) grown in a Yauhannah soil (fine-loamy, s iliceous, thermic Aquic Hapludults) at four P rates (0, 6.5, 11, and 2 2 mg kg(-1) soil), After the first wheat crop, the sludge was mixed th roughout the soil and a second crop grown, Surface-applied sludge decr eased wheat dry matter (DM) and P uptake, When incorporated, 4.45 g kg (-1) alum decreased DM and P uptake, Phosphate application increased D M and P uptake of the first wheat crop, but had no effect on the secon d crop, Surface-applied sludge increased AI-P, Pe-P, and Ca-P in the 0 - to 7,5-cm soil depth, but not in the 7.5- to 15-cm soil depth, Loose ly bound-P and AI-P increased with P rate, Phosphorus uptake and DM of the first wheat crop were positively related to loosely bound-P and M ehlich l-P, Dry matter of the second wheat crop was positively related to loosely bound-P and Mehlich l-P and P uptake was positively relate d to loosely bound-P, Aluminum-P was negatively related to P availabil ity indices, In alum sludge-affected soils applied P is immobilized ma inly as AI-P, and Mehlich 1-P and loosely bound-P are reliable estimat ors of P availability.