ORTHO-PHOSPHATE SOLUBILITY TRANSFORMATIONS AND AVAILABILITY FROM DUAL-APPLIED NITROGEN AND PHOSPHORUS - CALCAREOUS SOIL

Higher extractable P levels resulting from dual application (DApp) of ammoniacal-N and ammonium polyphosphate (APP) have been postulated to be a function of pH changes in the fertilizer injection zone of acid to neutral soils. The objective of this study was to characterize the injection zone of DApp of NH//4OH (to simulate NH//3 application) and APP to a pH-buffered calcareous soil (Weld sc1; Aridic Paleustolls). A previously studied acid soil, (Ascalon s1; Aridic Argiustolls), was used for comparison. The APP was applied to potted soil either alone or in DApp with NH//4OH. The injection zone soils were sampled through time and analyzed for P solubility and NaHCO//3-P. Solubility of P remained constant or increased up to 10 d after application of DApp of APP and NH//4OH to the calcareous soil. This treatment also enhanced NaHCO//3-P levels. Increased P solubilities and NaHCO//3-P levels were associated with slight pH decreases in the calcareous soil.