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Rationale for Optimum Nitrogen Fertilization in Corn Production¹

ABSTRACT

During the past decade, the percentage of the corn (Zea mays L.) acreage in the USA receiving N fertilizer has risen steadily. By 1971, in the Corn Belt and five adjoining states, this proportion ranged from 93 to 100% of the total corn acreage. Between 1964 and 1970 the average rate of N applied to fertilized acres increased about 83% in the Corn Belt and 128% in adjacent states (Nebraska, Kansas, Michigan, Wisconsin, and Minnesota). Undoubtedly, there has been an accompanying increase in the proportion of the corn acreage receiving optimum to excessive amounts of N fertilizer. These trends emphasize the importance of developing improved procedures for achieving optimum fertilizer N use (i.e., adequate but not excessive rates, and proper timing for greater efficiency) consistent with the goal of minimizing the possibility of environmental pollution.

The basic information required in predicting optimum use of N includes: (i) the internal N requirement of the crop for expected attainable yield, (ii) the amount of soil N mineralized during the cropping season, (iii) the amount of residual mineral N present the root zone early in the cropping season, and (iv) the expected efficiency of recovery of the plant-available N supply. With good management, efficiency, or % recovery of applied N by the grain and stover often is in the range of 50 to 70%. In this range, at near-optimum rates of N, essentially all of the unrecovered fertilizer N is subject to immobilization during decomposition of plant residues (stover and roots). At higher than optimum rates, however, a significant portion of the nitrate remains mobile and susceptible to loss by leaching or denitrification.

Key Words: denitrification • fertilizer N efficiency • ground water pollution

¹ Contribution from the U. S. Soils Laboratory, Agricultural Research Service, USDA, Beltsville, Md 20705.

² Soil Scientist.

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