Thermal Requirement and the Response of Corn Hybrids (Zea mays L.) to Different Planting Dates in Isfahan

To study the thermal requirements of grain corn hybrids¡ at different planting dates¡ a field experiment was carried out in the Agricultural Research Center of Isfahan¡ Iran in 2007 - 2008. It was conducted in split plot arrangement based on randomized complete block design with three replications. Planting dates (June¡ 5- June¡ 20 and July¡ 5) were assigned to main plots and hybrids (BC404¡ KSC320¡ OSSK552¡ KSC500¡ OSSK713 and KSC704) to sub plots. Results indicated that there was no significant difference for growing degree-days (GDD) requirements from planting to germination among hybrids and planting dates. However¡ KSC704 hybrid in the first planting date needed the highest GDD during its different growth stages. KSC 500 hybrid with 6.31 (t/ha) and OSSK 713 hybrid with 6.48 (t/ha) produced the highest grain yields. The highest number of grains per ear row belonged to KSC320 Hybrid (18.83). KSC704¡ OSSK713¡ OSSK 552¡ and BC404 possessed the highest kernels per ear row¡ 44.63¡ 44.59 and 44.74 kernels respectively. The highest thousand kernel weight (288.12 g) was also observed in BC 404 hybrids. The highest protein content was related to the third planting date. However¡ its percentages in all hybrids¡ except KSC 320 hybrid¡ were similar. KSC 500 hybrid had the highest phosphorous content (243 mg/100g). The highest plant disease incidences were observed in KSC 320 and KSC 404 hybrids. KSC 704 hybrid¡ in the mean time¡ showed the highest ear contamination percentage. The conclusion is that OSSK713 hybrid and the second planting date produced the highest seed yield in Isfahan¡ Iran.