Effect of Different Amounts of Nitrogen on Growth and Yield of Two Canola Cultivars (Brassica napus L.)in Two Saline S0ils

In Qom province، two thousand hectares are under canola cultivation، of which more than half suffer from different degrees of soil and water salinity. Nitrogen is one of the most important nutrients necessary for canola، especially in saline condition. There is no precise information about N nutrition for canola in saline condition. In order to study the effect of different N rates on growth and yield of two cultivars of canola in saline condition، during 2006-2007، two field trials were conducted in two sites in Qomroud district of Qom province. In the first farm، irrigation water and soil salinity levels were، respectively، 5. 5 and 5. 8 dS. m-1، and in the second site، the corresponding salinity levels were 8. 3 and 8. 1 dS. m-1. In each site، the trial was conducted with six levels of N and two canola cultivars in a split plots experiment with randomized complete blocks design and three replicates. Sub plots included nitrogen in six levels (i. e. 0، 45، 90، 135، 180 and 225 kg N. ha-1 as urea source) and the main plot was allocated to two canola cultivars، namely، Hyola-401 and PF varieties. The results showed that، for both cultivars and both irrigation water salinity levels، increasing N level up to 225 kg N. ha-1 enhanced seed yield، dry mater، and oil yield significantly (p<0. 05) in comparison with the control (no nitrogen application) and as well as the other N levels; however، the seed oil content decreased (p<0. 05). The Hyola-401 variety had comparative preference to PF variety in seed yield and oil content. Interaction between varieties and N levels was not significant. The highest seed yield was obtained in 225 kg. N. ha-1 at both salinity levels، whereas in PF variety in second salinity level، there was no significant difference between 180 and 225 kg. N. ha-1 at 5% level in Duncan test.