Effects of Harvest Date, Plant Density, and Hybrid on Corn Grain Quality

Corn (Zea mays L.) growers often question the effect of delayed fall harvest on grain quality. Various studies have reported the effect of genetic and environmental factors on the quality of grain, but few have reported on date of harvest. Therefore, the purpose of this study was to investigate the effects of harvest date, as well as planting density, hybrid, year, and their interactions on the quality of corn grain. Four hybrids were planted at 40,000, 60,000, and 80,000 plants/ha. Harvest dates were October 1, November 1, and December 1 each year of the 3-year study (1969–71). Grain quality was measured by determining protein and oil content, 1,000-kernel weight, test weight, and kernel hardness. Standard procedures were used for the first four variables and kernel hardness was determined on a Steinlite Model CK2 corn breakage tester. The only interactions to show significance were those of year with the other main effects. Protein content was not affected by delayed harvest, but did decline significantly with each 20,000 plant/ha increase in planting rate. Oil content varied more among hybrids (3.44 to 4.16%) than years (3.50 to 3.91%), and declined significantly as the harvest date was delayed (3.80 to 3.68%). Kernel weight and kernel breakage were closely related to the environment of the particular growing season. The range in 1,000-kernel weight among years was 68 g, whereas the maximum differences among hybrids was 34 g. Kernel breakage, an indication of kernel hardness, increased as population was increased from 40,000 to 60,000 plants/ha. When harvest was delayed from October 1 to November 1 kernel breakage increased. This study showed that protein content was not affected by delayed harvest and that kernel breakage was more closely related to the seasonal fluctuations in environmental conditions than to the treatments imposed. On the other hand, oil content showed a 0.12 percentage point decline as harvest was delayed. This decline, although significant, probably has little meaning from the milling point of view since the oil content of corn ranges from 4 to 5% of the whole kernel and not all the oil is extracted in the milling process. However, losses associated with delays in harvest as a result of increased stalk lodging and ear droppage were of greater significance.