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

Abstract

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 plants 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.

Potential for foliar phosphorus fertilisation of dryland cereal crops: a review

“…A large number of P compounds were applied to maize and soybean leaves, to determine the maximum amount that could be applied without damage to the leaves Black 1979a, 1979b). In the first of two studies 32 different foliar P compounds were tested (Barel and Black 1979a). The most successful compound tested on maize was ammonium tripolyphosphate followed by ammonium polyphosphate and phosphoryl triamide.…”

“…Silbertstein and Wittwer 1951;Garcia and Hanway 1976;Gray 1977;Alston 1979;Barel and Black 1979a;Parker and Boswell 1980;Harder et al 1982;Mallarino et al 2001;Ahmed et al 2006). These studies demonstrated that the salt load, pH and nutrient mixture all had important effects on the efficacy of foliar P fertiliser.…”

Determination of Optimum Rate and Growth Stage for Foliar‐Applied Phosphorus in Corn

“…Barel and Black (1979a) found that ammonium salts of orthophosphate dried rapidly and left dry crystals on the surface of the leaf, which depending on moisture availability and conditions such as temperature and humidity might be taken up later or washed away. In moist conditions, potassium phosphate is rapidly absorbed by leaf.…”

Methods to assay absorption of foliar applied nutrients and removal of unabsorbed residue1

“…To assay to the degree of foliar absorption, most studies utilize either rooted cuttings (9,10), seedlings (2,4,5,6,8) or excised leaves or discs to minimize space required for treatment (1,3,11). It is essential that the model system utilized reflects results that would be obtained by intact plants under actual practical application conditions.…”

“…Various methods have been employed including removal of the treated area (2,9,10), and rinsing or soaking in water (3,5,6,11), dilute acids and ions for exchange (4,6,7,6,12), or detergent solutions (1,12). Since many studies on foliar absorption require use of radioactive nutrients, many of these methods are undesirable due to personal safety and the increasing cost for disposal of large volumes of radioactive wastes.…”