Effects of sowing date on grain development trends in maize hybrids in Jiroft environment

In order to determine the effects of sowing date on grain development in four maize hybrids, a field experiment was carried out as a RCBD in split plot arrangement with three replications at experimental farm of Islamic Azad University of Jiroft, Iran (Lat. 26.43°N., Long. 56.17°E., Alt. 620 m.) in 2006. Main factor included four sowing dates (July 16, August 1, August 16 and September 1) and sub-factor included four hybrids (ZP434, BC504, NS540 and KSC704). During grain filling period, grain samples were taken in five different times and their grain dry weights were measured. Grain filling rate, effective filling period and kernel weight were determined. Results showed significant differences among the genotypes and sowing dates, while their interaction was not significant. Grain weight variation trends during grain filling period could be explained by an exponential equation. Delayed sowing date reduced the grain filling rate and grain weight by nearly 50% and 30%, respectively and increased the effective filling period by about 17%. The fastest grain filling rate was observed in NS504; hybrids KSC704 and ZP434 were moderate and NS540 showed the slowest grain filling rate.