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Nitrogen and Phosphorus Composition of Corn Leaves and Corn Yields in Relation to Critical Levels and Nutrient Balance¹

ABSTRACT

The relationship between corn yields and the N and P contents of corn leaves was determined in 93 fertilizer experiments by multiple curvilinear regression. The objective was to investigate critical levels and nutrient balance. Equal yields occurred at varying concentrations of N and P in the corn leaf within certain limits. The N or P content in the corn leaf at 95% of maximum yield varied with the concentration of the other nutrient because of their significant interaction on yield. Hence, the critical N or P level is not a point nor narrow range of values but includes a wide range of values depending on how it is defined and on the level of the other nutrient in the leaf. The N-P nutrient balance appeared to be critical only at or near the maximum yield. Nutrient unbalance may occur when the leaf N or P content extends beyond a certain limit in relation to the other one.

¹ Journal Paper No. J-3939 of the Iowa Agr. and Home Econ. Exp. Sta., Ames, Iowa. Project No. 1189. Contribution from the Department of Agronomy. Part of a thesis submitted in partial fulfillment for the Ph.D. degree by the author. This investigation was supported in part by a Research Grant provided by Swift and Company. Presented before Division IV, Soil Science Society of America, Cincinnati, Ohio, Nov. 18, 1959.

² Associate Professor of Soils, Iowa State University of Science and Technology. Grateful acknowledgement is made to John T. Pesek for his guidance and for some of the field data used in this study, to John J. Hanway for supervision of the corn leaf analyses and to H. R. Meldrum, all of the Department of Agronomy, for some of the field data used in this study and to E. H. Jebe formerly of the Department of Statistics under whose supervision the multiple regressions were calculated.

Received for publication August 15, 1960. Accepted for publication March 20, 1961.