Impact of planting date and hybrid on early growth of sweet corn
Sweet corn (Zea mays L. var. rugosa) is a warm-weather crop that is grown in most of the United States. Normally, it is planted over an extended planting window to provide a continuous supply for the fresh market. However, this planting window exposes the crop to various stresses and weather risks. The objective of this study was to determine the effect of planting date on early growth of sweet corn with different maturities for different environmental conditions in Georgia, USA. Three yellow sweet corn genotypes, including a full homozygous sugar enhanced (se), a super sweet (sh2), and a standard or normal (su), were compared in 2004, 2005, and 2006 in two locations in Georgia. The experiment consisted of one planting date in 2004, six in 2005, and four planting dates under two water regimes in 2006. Plant growth variables that were measured included leaf area index (LAI), canopy height, and aboveground biomass from emergence to the beginning of tasseling. The growth rate as a function of thermal time (TT) was used to determine the impact of planting date on growth of sweet corn. A base temperature (Tb) of 6.6°C for the three genotypes, obtained from experimental data, was used. Days to emergence varied from 4 to 12 for the warmest and coolest growing seasons, respectively. The growth of the three sweet corn genotypes showed a clear response to planting dates as LAI, canopy height, and aboveground biomass and the individual plant components, including stem, sheath, and leaves were significantly (P < 0.05) different at the beginning of tasseling. For all experiments, the longer the maturity group, the higher the total aboveground biomass. Significant differences (P < 0.05) for growth rate were found between planting dates, genotypes, plant components and their interactions. The short-season hybrid tended to have a faster overall plant growth rate of all individual plant components during the warmer seasons. In contrast, the mid- and full-season hybrids tended to have a higher growth rate during the cooler seasons. For rainfed conditions, the short-season hybrid had higher leaf and sheath growth rates than the mid- and full-season hybrids, resulting in a higher stem growth rate. These results indicate that the effect of planting date on early growth of sweet corn is of significance, as it may lead to identification of an optimum planting window for this crop.