Effects of Nitrogen Rates and Application Time on Agronomic Efficiency of Nitrogen and Seed Yield of Drylandʼs Wheat Genotypes

In order to study the effects of nitrogen rates and application time on nitrogen requirement، nitrogen use efficiency (NUE)، and dryland wheat genotypes quality and quantity this project was carried out in RCBD split plot of three cropping years (2006-2009) in Maragheh Dryland Agricultural Research Institute (DARI). The results showed that nitrogen application rates significantly increased grain، biological and straw yields، harvest index (H. I)، degree of productivity (DP)، number of spikes per unit area، plant height، head length، number of fertile tillers، number of seeds per head، plant weight، root fresh weight، root volume، and number of nodal roots. The highest nitrogen use efficiency was obtained for 30 kg N/ha and with increasing of nitrogen rates nitrogen use efficiency significantly increased in a linear manner. Dryland wheat mean nitrogen requirement، in order to achieve 90% grain yield was determined 50 kg of nitrogen per ha (100 kg urea per ha)، considering climate constraints such as cold early spring and drought stress. Using GGE Biplot analysis method the suitable nitrogen application times for Azar 2 and Homa cultivars were obtained in split forms (2/3 of nitrogen in autumn and 1/3 in spring) and for Sardari cultivar it was obtained in full application form by placement method in autumn، coincident with planting time. Also the results showed that application of nitrogen rates significantly increased the wheat grain protein concentration in a linear manner. Whithin nitrogen treatment ranges (0 to 120 kg N ha)، grain protein concentration increased 0. 025 percent for 1 Kg increment in application of the nitrogen per ha. The highest and lowest grain protein concentrations were obtained 11. 6% and 10. 4 % from Rasad (class A) and Sardari 101 (class B) cultivars، respectively. Finally، it was concluded that the nitrogen application rates and times could cahnge root characteristics، yield components، grain yield and nitrogen use efficiency in dryland wheat genotypes and they were effective on improving seed qualitative and quantitative characteristics.