Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Thomas C. Kaspar


Farmers are always looking for new management practices or enhancements to current cropping systems that will increase corn (Zea mays L.) grain yield per unit area. Improved plant genetics, fertility, plant populations, row widths, tillage practices, and pest management are some factors farmers have evaluated to determine if corn responds with increased grain yield. Corn has been produced in 0.76-m row widths for many years in North America. Much work has been done evaluating row width, plant population, and hybrid combinations over the years, but definitive answers remain elusive. Objectives of this research project were to compare corn response in 0.38- and 0.76-m row widths, to determine if plant populations and hybrids respond differently as row width narrows, and to look at the relationship of light quality in the canopy and grain yield. These results show that corn response to narrowing row widths from 0.76-m to 0.38-m had varying responses for grain yield and grain moisture. There was a trend for more consistent grain yield increases for corn grown in narrow rows and at higher plant populations in the NW region. In a given year within a region, the optimum plant populations for 0.38- and 0.76-m row widths were not different. Row width effects on the R:FR ratio were significant at one sampling date in each year. There was a trend for 0.76-m plots to have a higher R:FR ratio compared to 0.38-m plots across sampling dates. At all sampling dates in 1998 and 1999, the 93 860 plant ha-1 plots had lower R:FR ratio measurements. The erect-leaf hybrid, P3394, had higher R:FR ratio for most sampling dates when compared to the horizontal leaf-type hybrids, P3376 and P3618 in 1998 and 1999. These data suggest that canopy light quality is different for those hybrids that demonstrate upright leaf architecture compared to those with prostrate leaf architecture.



Digital Repository @ Iowa State University,

Copyright Owner

Steven Robert Paszkiewicz



Proquest ID


File Format


File Size

121 pages