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

ABSTRACT

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.

¹ Contribution 1483, Dept. of Agronomy, Kansas Agric. Exp. Sta. Portion of a thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. degree.

² Graduate Research Assistant and Research Soil Chemist, Dept. of Agronomy, Kansas State Univ., Manhattan, Ks. 66506.

Received for publication March 31, 1975. Accepted for publication July 17, 1975.