Management of developmental stages of six wheat varieties by changing planting dates and nitrogen fertilizer levels in the Rokh cold plain of Khorasan Razavi

To evaluate the effect of planting date and nitrogen fertilizer on various developmental stages of six wheat cultivars, this experiment was conducted using split split plot in a randomized complete block design with three replications in Rokh plain of Khorasan Razavi, Iran, in 2013-2014. The experimental factors were including planting date in three levels (October 10, November 5 and November 30) as main plots, nitrogen fertilizer in three levels (No fertilizer, 150 and 300 kg.ha-1) as sub plots and six wheat varieties (Zarin, Gascogne, Sayunz, Pishgam, Alvand and Mihan) as sub-sub plots. The results showed that varieties were significantly different at various developmental stages, so that Pishgam showed the highest and Mihan showed the lowest thermal needs from planting to rippening. A delay in planting reduced duration of developmental stages and consequiently reduced growth degree days (GDD), so that planting date from October 10 to November 30 caused a reduction of 656.7 GDD. Application of more nitrogen fertilizer increased duration of double ridges to end spikelet initiation (11.12%) and spikelet initiation to pollination stages (11.35%). The early developmental stages that determines the number of grains per spike as one of the main yield components, had the highest correlation coefficient with grain yield. Therefore, in case of delayed planting date of wheat, it would be possible to postpone wheat developmental stages by applying more nitrogen fertilizer. The results also indicated that in optimum planting date (October 10), Pishgam and in the late planting date (November 5 and 30), Alvand showed better performance than the other varieties.