Effects of date of planting and time of nitrogen application on spike development and yield of two wheat varieties

At the National Corn and Sorghum Research Centre, Pakchong, Nakornrachasima (lat. 14.7 0N and Loei series). A first experiment was carried out during November 1986 to February 1987 to investigate the effects of planting date on spike development and yield using split plot in CRD design with planting dates (12,23 Nov. and 3 Dec. 1986) and two wheat varieties (SW 29 and Sonora 64) were main plot and subplot, respectively. The second experiment, a study of effects of planting date and time of nitrogen application on spike development and yield, was conducted during November 1987 to February 1988. The split plot in RCB was employed with planting dates (12, 22 Nov. and 1 dec. 1987) were main plot and two wheat varieties times of nitrogen application (2 times) with 2 controls were subplot. The results form both experiments showed that time of spike development was longer in the first planting date. The spike development and duration of each growth phase was not affected by the time of nitrogen application. The growth of shoot was apex fairly slow in width and length during the first 35 day after sowing. The growth rate of shoot apex increased rapidly when the top spikelet was formed. Maximum yield of SW 29 and Sonora 64 was obtained from the first plating date which subsequently decreased in the later planting dated due to the number of spikelet per spike, the number of grains per spike and 1,000-grain weight which were found to be the highest in the first planting dates and subsequently decreased in the second and the third planting dates, respectively. Though, the number of spikelets per spike was increased by addition of nitrogenous fertilizer and 1,000-grains weight of SW 29 was higher than Sonora 64, with the same planting date, no yield difference was found neither between SW 29 and Sonora 64 nor both SW 29 and Sonora 64 with nitrogenous fertilizer adding. The difference in yield of wheat as affected by planting dates was most likely the result of 1,000-grains weight rather than any other components of yield