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This article in SSSAJ

  1. Vol. 39 No. 6, p. 1085-1088
    Received: Mar 31, 1975
    Accepted: July 17, 1975

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Reaction Products of Polyphosphates and Orthophosphates with Soils and Influence on Uptake of Phosphorus by Plants1

  1. Y. V. Subbarao and
  2. Roscoe Ellis Jr.2



Ammonium polyphosphate and diammonium phosphate were compared as sources of P for corn (Zea mays L.) in a growth chamber experiment with an alkaline-calcareous soil and a slightly-acid soil. Reaction products of the two P sources in soils and soil extracts correlated with results obtained in the growth chamber.

Applied P increased dry weights, uptake of P by the plants, and available soil P in the slightly acid soil. Both sources of P effectively supplied P for plant growth on this soil. Ammonium and magnesium orthophosphates, formed as reaction products in the laboratory experiments when the two P fertilizer materials were added, should furnish sufficient P for plant growth.

Neither source of P increased dry weights, uptake of P by plants, or available soil P in the alkaline-calcareous soil as much as with the slightly-acid soil. Dry weights of plants and uptake of P were significantly less with polyphosphate than with orthophosphate, both at 36 ppm applied P. Polyphosphate also failed to increase the available soil P. A reaction product, Ca(NH4)2P2O7·H2O, that is highly stable in alkaline-calcareous soil was formed when ammonium polyphosphate was added. Its stability and low solubility explain the limited availability of P. The compounds, Mg2KH(PO4)2·15H2O and Ca4H(PO4)3·2.5 H2O, formed when diammonium phosphate was added. They provided more P for plants at the highest rate of application, but uptake of P was limited for both sources of P in this soil.

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