The effects of reduced tillage, time of fertilizer application, and plant population level on a diverse set of corn (Zea mays L.) genotypes

A diverse set of corn (Zea mays. L.) genotypes was grown at the Plant Science Field Laboratory, Knoxville, Tennessee, and at the Plateau Experiment Station, Crossville, Tennessee, in 1980. The objective of the experiment was to evaluate the effects of various environmental conditions on agronomic performance. Environmental effects were location, time of nitrogen fertilizer application, and plant population level. Yield and ten other traits were measured on eight F_{1 hybrids, five open-pollinated varieties, and three exotic varieties. Severe environmental conditions resulting from below normal rainfall occurred at both locations in 1980.}

Open-pollinated and exotic varieties did not outperform hybrids with respect to yield under any combination of treatments. Hybrids were less responsive to environmental differences due to population level, fertility, or location than were varieties.

Significant location differences were found, with performance being better at Knoxville than at Crossville for most traits measured. Plant population level also had a significant effect on performance. Yields were highest at the intermediate population density of 43,000 plants per hectare. Stalk lodging increased, while prolificacy and tillering decreased, as population density increased from 25,000 to 61,000 plants per hectare. Variation in the timing of nitrogen fertilizer application had little effect on the traits studied. When the entries were divided into hybrids, open-pollinated varieties and exotics, significant differences among these type groupings occurred for all independent variables.

There was no indication from the characteristics evaluated in this study that genetically heterogenous varieties would be preferred over hybrids in the set of environmental conditions considered. It would appear that, at least in the short term, germplasm selected for high yield using current cultural practices would be the preferred germplasm source for hybrid development under slightly modified cultural practices.