The Effect of Nitrogen Supplies at Flowering on Dry Matter Production and Distribution, the Relationship Between Source Strength and Sink Size, and Yield Formation Processes in Wheat, Barley and Triticale

In order to compare the yield response of wheat, barley and triticale to nitrogen, a split plot experiment was conducted in Mashhad during the 2017-2018 crop year. Nitrogen factor with two levels of non-foliar application (N1) and application of urea fertilizer 46% in the flowering stage at a rate of 20 kg / ha (N2) were allotted to the main plots and cereal type factor in the subplots. The results showed that N2 treatment increased grain yield by 12.6%, which was mainly due to the increase in the contribution of current photosynthesis in grain yield formation from 43.6 to 51.2% and had little relationship with the efficiency of dry matter distribution to grain. Also, N2 treatment, despite a significant reduction in 1000-seed weight, increased the number of seeds per spike by 20.9% and grain weight per spike by 12.9%. Nitrogen foliar application increased the contribution of current photosynthesis in grain yield formation from 43.6% to 51.2% and decreased the rule of stem dry matter remobilization in yield formation from 72.4% to 53.4%. Despite having the same harvest index as wheat, triticale had 13.3% higher grain yield than wheat due to its higher biological yield. The amount of current photosynthesis in triticale was %46.8 more than wheat, but the relative contribution of stem reserves to yield formation was not significantly different. The main reason for the higher in triticale compared to wheat was the higher number of grains per spike, and the difference in grain weight was less important. The results indicate that grain weight is not affected by nitrogen uptake and transport processes and is mostly a function of photosynthesis. Based on these results, the source-sink balance in triticale resulted in higher yield of it compared to wheat and barley. It seems that nitrogen in the flowering stage can increase the yield of wheat and barley by preventing abortion of florets and increasing the size of the reservoir as well as improving the strength of the source by increasing the current photosynthesis.