Orthophosphate Solubility Transformations and Availability from Dual-Applied Nitrogen and Phosphorus: Calcareous Soil1
- R. L. Hanson and
- D. G. Westfall2
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 NH4OH (to simulate NH3 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 NH4OH. The injection zone soils were sampled through time and analyzed for P solubility and NaHCO3-P. Solubility of P remained constant or increased up to 10 d after application of DApp of APP and NH4OH to the calcareous soil. This treatment also enhanced NaHCO3-P levels. Increased P solubilities and NaHCO3-P levels were associated with slight pH decreases in the calcareous soil. This change in pH is postulated to be due to nitrification of the ammoniacal-N; microsite pH change is undoubtedly much greater than what was measured in the whole soil mass and probably influenced P availability and solubility substantially.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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