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Fig. 3. Recovery of 33P during sequential extraction of soils continuous maize (COM) and maize-crotalaria fallow rotation (MCF) after addition of 6 mg P kg–1 soil as plant residue or inorganic phosphorus (added Pi), both labeled with 33P, or after carrier-free labeling of isotopically exchangeable phosphorus (soil IEP). Resin-extractable phosphorus (Presin) determined separately; phosphorus extracted with resin membranes in the presence of hexanol (Pfum) and inorganic and organic phosphorus extracted with 0.1 M NaOH separated by acidification-centrifugation (NaOH-Pi and -Po) extracted sequentially. Bars show SD of the sum of 33P recovered in Pfum, NaOH-Pi, and Na-OH-Po.
