Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Kendall R. Lamkey


Pollution of water resources from the overapplication of fertilizer nitrogen (N) has become a recent environmental concern. To maintain yields, while reducing fertilizer N use, N-efficient maize (Zea mays L.) cultivars need to be identified. Experiments were conducted in 1988, 1989, and 1990 (i) to evaluate the response of 60 unselected S[subscript]3 lines and 30 S[subscript]3 x S[subscript]3 crosses of two maize synthetics, BS24 and BS25, to rates of N fertilizer; (ii) to determine the feasibility of selection of maize cultivars for increased N-use efficiency (NUE); (iii) to evaluate the contribution of the components of NUE, N-uptake efficiency (UPE) and N-utilization efficiency (UTE), to the variation of NUE in BS24 and BS25; and (iv) to determine the effects of long-term breeding efforts for increased grain yield on NUE, UPE, and UTE by evaluating these traits in populations representing seven eras of maize breeding. Genotypes were grown at one location each year with four soil-applied N treatments: 0, 80, 160, and 240 kg N ha[superscript]-1. Grain yield and total plant N generally increased with increasing N rate, with the largest increase occurring across the first N increment. NUE and UPE showed drastic declines across N rates, whereas UTE was unaffected by N treatment. Significant (P ≤ 0.05) genotypic variation and adequate heritability estimates for NUE, UPE, and UTE were found among progenies from both synthetics. A wide range of genotypic responses of NUE to increasing N rates was also noted suggesting selection for increased NUE should be possible. At each N rate, UTE accounted for over 66% of the variation in NUE for the two synthetics, while UPE was the primary component in the S[subscript]3 x S[subscript]3 crosses. This suggests that the conversion of N into grain yield was a yield-limiting factor in the S[subscript]3 lines, whereas N uptake may be limiting grain yield of the S[subscript]3 x S[subscript]3 crosses. This study also found that long-term breeding efforts for improved grain yield had significantly increased NUE and also resulted in a positive, linear increase in UPE (P ≤ 0.10). UTE was not affected by long-term breeding efforts.



Digital Repository @ Iowa State University,

Copyright Owner

Kenneth Allen Dallmier



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162 pages