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Influences of Varying Plant Population, Soil Fertility and Hybrid on Corn Yields¹

ABSTRACT

Four experiments on widely different soil types were carried out in 1952 to study the influences of varying plant population, fertility level, and hybrid on yield of corn grain and on plant characteristics. Selected hybrids of three maturity ratings were used at each location.

Corn yields were increased by an application of fertilizer, assumed to be adequate, at all locations. The degree of response to applied fertilizer was influenced by plant population level, the initial fertility level of the soil, and to a lesser extent by the hybrids grown. Yield increases attributable to fertilizer ranged from 7.5 to 101.9 bushels per acre.

Grain yields of all hybrids were increased on the high fertility level plots by increasing plant populations above 8,000 plants per acre. Lowest yields at this fertility level occurred at the lowest population and best yields were obtained at the highest population (approximately 24,000 plants per acre). Yield responses to different populations were not consistent at the low fertility level. Responses varied with higher populations from slight increases to slight, but consistent decreases. Yield differences attributable to increasing plant populations from 8,000 to 24,000 plants, ranged from a decrease of 22.7 on the lowest fertility level to an increase of 64.8 bushels on the high fertility level. Intermediate populations at both fertility levels resulted in intermediate yield differences.

The "late" hybrid on the high fertility level generally produced higher yields than the "adapted" and "early" hybrids up to 16,000 plants per acre. Above this population the adapted hybrid was generally equal or higher in yield.

There were small and inconsistent differences between hybrids at the low fertility level. Any general yield advantages favored the adapted and early hybrids over the late hybrid.

¹ Contribution from the Department of Agronomy and the Agr. Ext. Service, Journal Paper No. J 2454 of the Iowa Agr. Exp. Sta., Ames, Iowa. Project Nos. 1148 and 1140. Presented before Section IV, Soil Science Society of America, Dallas, Texas, Nov. 19, 1953.

² Extension Agronomist, Iowa State College. This study was made possible by the cooperation of members of the Agronomy Department, Iowa State College, and the Division of Soils and Agronomy and Plant Genetics, University of Minnesota.

Received for publication December 28, 1953.