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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.

Abstract:Iron (Fe) deficiency is a yield-limiting factor for a variety of field crops across the world and generally results from the interaction of limited soil Fe bioavailability and susceptible genotype cultivation. Iron deficiency broadly occurs across the world in soybean, peanut, dry bean, sorghum, and rice but sporadically under unique or specialized conditions with corn, wheat, and oat. In this chapter, soil properties associated with the expression of Fe deficiency in field crops are defined, and biochemical interactions that promote field observed Fe-deficiency problems are explored. Strategies examined for use with field crops where Fe deficiency is a concern include cultivar selection and screening for tolerance, fertilizer and cultural practices, lowering soil pH, foliar sprays, chelated and complexed Fe fertilizers, concentrated fertilizers, mixed cultivar and companion crop interactions, and management of irrigation and drainage, fertility and seeding practices. Finally, we identify areas where future research is needed.

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