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Response of Maize Inbred Lines to N Fertilizer¹

Maize (Zea mays L.) inbred lines are the parents of single-cross hybrids, yet few studies have been reported with inbred lines as the experimental material in N fertilizer studies. The genetic materials in this field study were 10 inbred lines. The objectives were to determine: 1) inbred line response to sidedress N fertilizer, 2) rate of N for maximum grain yield, and 3) inbred line response to N-fertilizer treatments. The N treatments were: check (0 kg/ha), three levels of preplant broadcast (60, 120, and 180 kg/ha), and three levels of preplant-sidedress (30-30, 60-60, and 9090 kg/ha). Soil types involved were Typic Haplaquolls and Cumuli Haplaquolls. Data were obtained for 12 plant, ear, and grain traits in four environments. Growth conditions differed greatly among the environments. There was no yield response in one environment, a small response in two environments, and a large response in one environment. Generally, the greatest yield response was for the first N increment (60 kg/ha), and only in the environment with the greatest response did further N increments give important yield increases. The preplant vs. preplant-sidedress comparison showed no significant yield differences in any environment. In the environment that had the greatest response to N treatments, there were significant differences among the inbred lines; i.e., a significant inbred x N interaction was observed. One line had no response, five lines had significant linear responses, and four lines had significant quadratic responses. Ear length, ears per plant, and kernel weight were the most important yield components, but the relative importance of these components varied among the inbreds. Effects of N treatments generally were of no practical importance for plant and ear height, but pollen shed and silk emergence were significantly earlier in the environment with the greatest yield response.

Key Words: Zea mays L. • N fertilizer levels • Genotype x treatment interactions

² Maize breeder, Northrup King Co., Washington, IA 52353 (formerly graduate assistant, Iowa State Univ.) and professor of plant breeding, Iowa State Univ., Ames, IA 50011.

Received for publication December 17, 1979.