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To study the effects of different levels of nitrogen fertilizer on yield and yield components of cultivars of rainfed wheat a study was done in the crop year 2012-2013 as factorial in a randomized complete block design with 3 replications, in 2 research stations of Kohne Kand city in Bojnord and Shirvan dryland research station. The treatments of study contain cultivars of wheat in 4 levels (Rasad, Sabalan, Cross Sabalan and Azar 2) and 4 levels of nitrogen fertilizer (75, 50, 25 and 0 kilograms nitrogen per hectare). The results showed that the yield in Shirvan was significantly higher than that in Bojnoord. Moreover, the impact of cultivar and nitrogen on yield and yield components was significant in both regions and among different cultivars Azar 2 has the highest yield in both regions and the lowest yield was for cross Sabalsn in Shirvan and Sabalan in Bojnoord. Furthermore, yield increased by increasing the nitrogen in both regions but there was no significant difference between levels 50 and 75 kilograms per hectare. Among yield components except the number of spikes per square meter, others had a high correlation with yield.

Pre-anthesis stored dry matter in wheat (Triticum aestivum L.) is important in a Mediterranean climate because grain filling greatly depends on the remobilization of pre-anthesis assimilates. A water deficit at the post-anthesis stage may increase the dry matter stored before anthesis. This field study assessed the effects of post-anthesis water deficit and the application of nitrogen (N) fertilizer on three wheat cultivars. Data collected over 2 years showed that, in wheat with a post-anthesis water deficit (WD), dry matter remobilization efficiency reached its maximum (29%) at 80 kg N ha(1 , but further additions of N decreased it. The contribution of remobilized dry matter to a grain ranged from 7% to 23% of the grain's dry weight and, in WD grain, was 78% more than that of well-watered (WW) grain. Grain from plots on which fertilizer had been applied had a lower proportion of remobilized dry matter than did grain from unfertilized plots. For grain from adequately fertilized treatments, limited irrigation was associated with reduced dry matter remobilization. The amount of non-structural carbohydrates (NSC) remaining in parts of the plant was much greater in the WW than in the WD treatments. The 160 kg N ha (1 treatment also left more NSC unused than did the no N treatment. The active grain-filling period was shortened substantially by a water deficit, but this was countered by the application of 160 kg N ha (1 . Grain-filling rates for all cultivars or all N treatments were increased by inducing a water deficit. For WD grains, kernel weight was reduced when fertilizer application rates were 0Á80 kg N ha (1 , but increased when rates were 160 kg N ha(1 , unlike WW grain exposed to similar fertilizer regimes. The grain yield of WD wheat was reduced by 25%, and that of grain receiving no fertilizer was 15% lower than that receiving 80 kg N ha (1 . Among three wheat cultivars, cv. Chamran produced the highest grain yield (19% higher than that of either cv. Shiraz or cv. Marvdasht). It was concluded that the stored carbohydrate had provided an important buffer against water stress during grain filling, in terms of yield.

Pre-anthesis stored nitrogen in wheat (Triticum aestivum L.) is important because grain filling greatly depends on the remobilization of pre-anthesis nitrogen under Mediterranean growth conditions. This field study was conducted to assess the effect of post-anthesis water deficit and three N fertilizer levels on N remobilization and N losses in three wheat cultivars ('Shiraz', 'Marvdasht' and 'Chamran'). Nitrogen remobilization in plant parts decreased to 29 to 58% under water deficit compared with the well watered (WW) treatment. Grain N was 40% higher under post-anthesis water deficit than the WW treatment and with the addition of 160 kg N ha-1. The application of nitrogen fertilizer increased N remobilization to 78%. 'Shiraz' remobilized 13 and 25% more nitrogen than 'Marvdasht' and 'Chamran', respectively. Under water deficit, N remobilization efficiency increased by 13%. Leaves were more efficient than stem and spike in N remobilization efficiency either in the WW or the WD treatment. The application of fertilizer N generally lowered whole plant remobilization efficiency. The N remobilization efficiency of 'Chamran' increased when the soil moisture and/or N were limited during the grain filling period. Grain N concentration was correlated positively with N concentration or N content of vegetative parts at anthesis. In addition to nitrogen fertilizer, WD during grain filling reduced nitrogen use efficiency by 30 and 25%, respectively. In the WW treatment, 25% of the N at anthesis was lost at maturity. In contrast, under WD only 6% of the N was lost. High amount of N led to N losses at maturity. Significant negative correlations were found between grain yield and grain protein concentration in the three wheat cultivars. Results indicate that the greater the amount of N accumulated before anthesis, the higher the translocation rates of nitrogen to grain and the greater the risk of net N losses at maturity.

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