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Relationship Between Corn Yield, Expressed as a Percentage of Maximum, and the N Percentage in the Grain. I. Various N-rate Experiments¹

The objective of this investigation was to determine if the N content of the grain of corn (Zea mays L.) could be used as a measure of N sufficiency of the crop for maximum yield. This was done by studying the relationship between yield, expressed as a percentage of maximum, and the N percentage in the grain. The relationship was determined from the data of 13 site-years of six N-rate experiments in Iowa and from data reported in the literature.

Two methods, a graphical and a regression method, were developed to relate the yield of corn, expressed as a percentage of maximum, and the N percentage in the grain. Good agreement was found between the two methods for obtaining maximum yields and N percentages at various percentages of maximum yield. The average critical N percentages, or percentages at maximum yield, by the graphical and regression methods, were 1.52% and 1.54%, respectively, for the Iowa experiments. The data calculated from the experiments reported in the literature were in general agreement with the Iowa data.

The standard error of the mean of the critical N percentages (graphical method) for the 13 site-years of Iowa experiments was 0.016% and, for the 24 site-years of the non-Iowa experiments, it was 0.022%. Some of the variability may have been caused by differences among the 23 hybrids represented in the experiments. Moisture stress, plant density, and adequacy of other nutrients had little or no demonstrable effect on the relative yield — percent N relationship.

It is concluded that the relative yield — percent N relationship offers a promising and practical basis for estimating N sufficiency and the N requirement for maximum yield, or for an economic optimum yield.

Key Words: Critical N percentage • N sufficiency • Plant analysis • Relative yields • Protein increases from N fertilizers • Relative yield — percent N relationship

² Professor emeritus, associate professor, research associate, and professors of agronomy, respectively.

Received for publication April 17, 1976.

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