evaluation of planting date and nitrogen effects on the development stages of wheat cultivars and their relationship with yield and yield components in nishabur

abstractbackground and objectives: all changes in the development stages of plants results in the change of one or more yield components and finally, the ultimate yield and manipulation of these periods means to create new possibilities for increasing yield. accordingly, planting date has a significant impact on plant growth and development during the growth season, so that any shift in planting date may drastically change the development stages. the purpose of the current study is to explore the relationship between yield and yield components with different phonological stages of wheat cultivars in nishabur region and examine the possibility of increased yield by changing these stages using management methods. materials and methods: to evaluate the effects of different development stages on yield and yield components of wheat under treatments of sowing date, nitrogen fertilizer and cultivar, an experiment was conducted as split-split plot with complete randomized block design and three replications at the agricultural research station of nishabur in 2013. the experimental treatments included three sowing dates (9th oct., 8th nov. and 8th dec.) as the main plot, nitrogen fertilizer in three levels (75 kg ha-1 as pre planting fertilizer and 150 and 300 kg ha-1 urea (46% n content) in two times at jointing and heading stages) as the sub-plot, and six spring wheat cultivars (bahar, parsi, pishtaz, chamran, sirvan and sivand) as sub-sub-plots. results: experimental results indicated that delay in sowing date caused a decrease in the duration of developmental stages especially in the vegetative growth period. growth period was increased by enhancing the amount of nitrogen fertilizer. therefore, the thermal requirement for going through the development stages was increased. among the numerous varieties of wheat, syvand (2362.9 gdd) and parsi (2299.8 gdd) cultivars had the highest and lowest required growing degree- day (gdd) from sowing time to maturity, respectively. also, the results of stepwise regression indicated that the duration of the period from sowing to double ridge emergence had the highest relationship with grain yield fluctuations compared with other development stages. moreover, a high correlation was observed between this period and the number of spikes/m2. conclusion: wheat which have a longer period from sowing time to double ridge emergence have higher number of spikes/m2 and they are more likely to have higher grain yield in the climatic conditions of nishabur. according to the results, wheat cultivation in october and application of nitrogen fertilizer can be recommended for increasing the vegetative growth period (especially from cultivation to double ridge stage that showed the highest relation with the number of spikes per square meter) and producing higher yield in the region.