| A series of experiments were conducted during 1986, 1987, and 1988 at different locations in Ohio to determine the effects of certain cultural practices on selected physical (commercially desirable) as well as chemical (nutritionally desirable) properties of different corn (Zea mays L.) hybrids. Specifically, the following questions were investigated: (a) the effects of plant population and planting date on grain yield, kernel hardness, grain N concentration, and N yield, and (b) the response of six endosperm types to two levels of N fertilization with respect to grain yield, kernel hardness, and protein quality. In both of the above questions, kernel hardness was measured by a combination of parameters: grinding resistance, kernel density, and breakage susceptibility.;In the first series of experiments (a), results showed that cultural practices enhancing grain yield tended not to enhance nutritional value of the corn, and that those cultural practices enhancing corn grain nutritional value did not enhance grain yield. Increasing the number of plants/ha increased grain yield but reduced N concentration in the grain. In contrast, delaying planting date enhanced N concentration and overall kernel hardness, but reduced grain yield. A positive relationship between the chemical property of N concentration and the physical property of kernel hardness was observed, however.;In the second series of experiments (b), N fertilization at the higher level increased overall kernel hardness due to the increased N concentration in the grain, and apparently reduced breakage susceptibility in most hybrids. Furthermore, at this N fertilization rate, protein quantity increased, but the overall protein quality decreased in some of the hybrids due to the disproportionate increase of lower quality zein content. These findings suggest a positive relationship between zein protein content and kernel hardness in corn grain. Finally, because of drought conditions in 1988, the higher level of N fertilization failed to increase grain yield except in the soft endosperm hybrid at Columbus, where moisture level was optimal. |
