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Soil Test Phosphorus and Solubility Relationships in Calcareous Soils
Author(s) -
Havlin J. L.,
Westfall D. G.
Publication year - 1984
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1984.03615995004800020021x
Subject(s) - solubility , monocalcium phosphate , loam , phosphorus , chemistry , fertilizer , calcareous , soil water , phosphorite , phosphate , agronomy , zoology , nuclear chemistry , environmental chemistry , mineralogy , geology , soil science , biochemistry , organic chemistry , paleontology , fishery , fish <actinopterygii> , fish meal , biology
Irrigated alfalfa ( Medicago sativa L.) was established in 1976 on two Colorado Soils [Keith clay loam (Aridic Argiustolls) and Ravola loam (Typic Torrifluvents)] to determine the residual value of fertilizer P. Triple superphosphate was applied annually at rates of 25 and 50 kg P ha −1 , with 75 kg P ha −1 applied triennially and at seeding. Phosphorus solubility (in 0.01 M CaCl 2 ) and NaHCO 3 ex tractable P were measured initially and in the third and sixth years of the study. The resulting calcium hydroxide (Ca(OH) 2 ) and monocalcium phosphate (Ca(H 2 PO 4 ) 2 ) potentials were related to known solubility products for distinct mineral phases. Phosphorus solubility in the 0‐ to 7.5‐cm depth increased in all fertilized treatments after three years in both soils. No further increases in P solubility, NaHCO 3 ‐P, or P uptake were observed over the next 3 yr. According to solubility diagrams residues of octacalcium phosphate (OCP) were apparently accumulating in the surface 7.5‐cm layer at NaHCO 3 ‐P levels >32 mg kg −1 . Below this extractable P level β‐tricalcium phosphate (TCP) apparently controlled P solubility.