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Effects of Ammonium Polyphosphates on Yield¹ and Chemical Composition of Irrigated Corn

Irrigated corn (Zea mays L.) grown on Zn-deficient, slightly acid Cass fine sandy loam suffered from increasingly severe Zn deficiency when 40 kg/ha P (80 lb/A P₂O₅) was applied in a band to the side and below the seed. Zinc deficiency was corrected in the presence of the banded P when Zn was supplied at the rate of 11.2 kg Zn/ha as ZnSO₄.

Banded applications of ammonium polyphosphate (APP) in the presence of inadequate Zn tended to induce more severe Zn deficiencies than did similar applications of monoammonium phosphate (MAP). When adequate Zn was supplied, the two forms of P produced comparable plant growth responses and grain yields. Yield depressions noted with the use of banded APP without adequate Zn were associated with higher plant P contents than when the plants were supplied with MAP. High levels of plant P were concomitant with low levels of Zn in the plants. Banded applications of P resulted in higher plant concentrations of P than did broadcast P applications and induced more severe Zn deficiencies.

When Zn was limiting, grain yields tended to decrease with increasing P concentrations in young plant tissues. In the presence of adequate Zn concentration of P in young plant tissues was positively correlated with grain yields.

Key Words: Pyrophosphate • Orthophosphate • P-Zn interaction

² Research Assistant (now Postdoctoral Research Fellow, Department of Soils and Plant Nutrition, University of California, Riverside) and Associate Professor, Department of Agronomy. Kansas State University, Manhattan 66502

Received for publication October 3, 1969.