Degree Type


Date of Award


Degree Name

Doctor of Philosophy




A study was conducted to evaluate hybrids, plant populations, and harvest dates for forage corn (Zea mays L.) yield and quality traits. Five open-pedigree hybirds of different relative maturities were grown at Nashua, Iowa in 1978, 1979, and 1980 at three plant population densities (50,423, 64,829, and 79,235 plants per hectare). A split-plot design was used for traits related to grain yield and a split-split-plot for traits related to forage production. Three different harvest dates (30, 45, and 60 days after mid-silk) were used to determine the relative values for forage traits;Combined analyses of variance detected significant linear effects among plant populations for all traits except mature grain weight, moisture content of mature grain, mature grain corrected for moisture, and harvest index. Harvest index did not show significant effects among plant populations. Increases in dry matter yield and decreases in dry matter content corresponded to increases in plant population. An average increase of 10% was observed among population levels for dry matter yield;Differences among hybrids were detected in the combined analyses of variance for all traits except dried ear weight and dried grain weight. The latest maturity hybrid (B73 Ht x Mo17 Ht) was higher and the earliest maturing hybrid (A619 Ht x A632 Ht) was lower in dry matter yield; an average increase of 20.3% in dry matter yield would be possible with the latest hybrid;Differences among harvest dates in the combined analyses were significant for green stover weight, dried ear weight, dried grain weight, and harvest index, indicating linear effects;Phenotypic and genotypic correlations between traits for all hybrids, such as between mature grain yield corrected for moisture and dried stover weight (0.605 and 0.597), mature grain corrected for moisture and days to mid-silk (0.763 and 0.804), and dried plant weight and days to mid-silk (0.992 and 1.00), were estimated;Relatively later maturing hybrids had acceptable levels of dry matter, crude protein, and digestible dry matter and could possibly be used for forage corn production in short season areas. Further research on qualitative and quantitative forage traits are necessary for developing breeding programs for forage corn.



Digital Repository @ Iowa State University,

Copyright Owner

Jairo Silva



Proquest ID


File Format


File Size

139 pages