CHANGES WITH TIME IN THE FORM AND AVAILABILITY OF RESIDUAL FERTILIZER PHOSPHORUS ON CHERNOZEMIC SOILS

Abstract

A sequential phosphorus (P) fractionation procedure was used to measure the changes in the labile and stable forms of inorganic and organic P following single broadcast P applications to Canadian Chernozemic soils under cereal cropping. Approximately half of the fertilizer residues remained in plant-available forms (resin, NaHCO 3 ). In a Black Waskada clay loam 8 yr after the application of 200 and 400 kg P ha −1 , residual fertilizer P consisted of resin-P, 30–40%; HCl-P, 25–30%; residue-P, 10–15%; NaOH-P, 10–15%, NaHCO 3 -P, 10%; and aggregate protected P, 3%. The residues in a Dark Brown Sutherland clay 5 yr after the application of 160 kg P ha −1 were: resin-P, 35%; NaOH-P, 30–40%; NaHCO 3 -P, 15%; HCl-P, 0–5%; H 2 SO 4 -P, 5%; and aggregate protected P, 5%. The soils differed in the quantity of fertilizer recovered in inorganic HCl-extractable forms. In the Sutherland soil the change from wheat-fallow to continuous wheat cropping produced a build-up of organic P which occurred with and without the addition of P fertilizer. Key words: Residual P, P transformations, Labile P i; labile P o , stable P i stable P o