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Orthophosphate Solubility Transformations and Availability from Dual Applied Nitrogen and Phosphorus
Author(s) -
Hanson R. L.,
Westfall D. G.
Publication year - 1985
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/sssaj1985.03615995004900050043x
Subject(s) - solubility , chemistry , monocalcium phosphate , phosphate , alkali soil , phosphorus , anhydrous , nitrification , ammonium polyphosphate , ammonium , soil water , fertilizer , ammonia , nuclear chemistry , nitrogen , inorganic chemistry , organic chemistry , geology , raw material , fishery , fish <actinopterygii> , soil science , fish meal , biology
Knife applications of NH + 4 ‐N and P fertilizers into common injection zones (dual N and P) have produced higher crop yields and P absorption than other N and P application methods. Enhanced solubility of the P fertilizer reaction products due to the presence of NH + 4 could account, in part, for these crop responses. Greenhouse studies were conducted to characterize P reaction product solubility transformations and P availability in dual N and P injection zones. Treatments were ammonium polyphosphate (APP) + NH 4 OH (used to simulate anhydrous ammonia), NH 4 OH or KNO 3 + nitrapyrin solutions injected simultaneously (dual N and P application) into four different soils (Aridic Argiustolls, Udic Argiustolls, Mollic Albaqualfs, and Typic Argiborolls). Monocalcium phosphate potentials and NaHCO 3 or Bray extractable P were used to characterize P solubility and availability relationships in the injection zones. Dual application of NH 4 OH plus APP with and without nitrapyrin resulted in increased NaHCO 3 or Bray‐extractable P in three of the four soils. The mechanisms that resulted in higher extractable P are concluded to be associated with the high injection zone pH caused by NH 4 OH applications. The postulated mechanisms are: (i) the initial high (alkaline) pH immediately after dual application allows formation of highly available Ca‐P reaction products as opposed to less available Al‐ and Fe‐P reaction products that exist in slightly acid soils, (ii) then the production of H + during nitrification increases P solubility as phosphate potentials move up the dicalcium phosphate dihydrate and dicalcium phosphate isotherms, and (iii) this rapidly decreasing pH allows the soluble reaction products to persist which results in higher P availability and solubility for a longer period of time. Inclusion of nitrapyrin (a nitrification inhibitor) prolonged the time of Ca‐P reaction product persistence in the injection zone. Dual KNO 3 + APP applications resulted in suppressed P availability, as compared to NH 4 OH + APP, apparently due to formation of less soluble reaction products. This suppressed P availability could account for the relative ineffectiveness of NO ‐ 3 ‐N in dual application.