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Agronomy Journal Abstract -

Foliar Application of P. I. Screening of Various Inorganic and Organic P Compounds1


This article in AJ

  1. Vol. 71 No. 1, p. 15-21
    Received: Oct 25, 1977

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  1. D. Barel and
  2. C. A. Black2



The suitability of 32 different P compounds for foliar application was tested by using a new technique in which predetermined quantities of P were applied to a fixed leaf area. This made it possible to obtain quantitative data on absorption of added P and on translocation of absorbed P out of the treated area. Presently foliar applications of P are used less than N, one reason being that no P compound is available which can be sprayed on planta in large enough quantities without damaging the leaves. Several representatives of the condensed phosphates and some compounds containing P-N bonds or P-N-P linkages proved promising. Both group of compounds hydrolyze spontaneously to release orthophosphate, and all share the quality of delayed action. These P sources could be applied at 2.5 to 3 times the quantity of P that could be applied as orthophosphate in a greenhouse experiment without causing leaf damage. The most successful compound for corn (Zea mays L.) was ammonium tripolyphosphate, which could be applied at 370 µg of P/cm2 without causing leaf damage; 66% of the applied P was absorbed within 10 days, and 87% of the absorbed P was translocated out of the area of application in the same period. Other successful compounds for corn were ammonium tetrapolyphosphate and phosphoryl triamide. Soybeans (Glycine max L. Merr.) proved more sensitive than corn and could, in general, tolerate only two-thirds to three-fourths of the quantity of the various compounds that could be applied to corn, with the exception of phosphonitrilic hexaamide, which could be applied at 340 µg of P/cm2. Ammonium tri- and tetrapolyphosphate could be applied at 220 µg of P/cm2 to soybeans. Rapid intake is suspected to be an important reason for the damage observed with orthophosphate. Several organic P compounds were tested, but none of them was superior to the condensed P sources.

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