Turnip rape yield and yield components response to different sowing dates under different irrigation regimes

Water stress is the most important factor limiting crops production in the world. Water stress effect could be modified in different ways such as choosing the most appropriate sowing date. To assess the effect of sowing date on yield and yield components of turnip rape (Brassica campestris L.-cv. Goldrush) under different irrigation regimes, a field experiment was conducted in Qazvin, Iran during 2010 to 2011 growing season. The experiment was laid out in a three-replicated-randomized complete block, factorial design with four irrigation levels (I: I1= normal irrigation (control), I2= interruption of irrigation from flowering stage, I3= interruption of irrigation from silique formation stage and I4= interruption of irrigation from seed filling stage) and four sowing date levels (D: D1= 2 October 2010, D2= 12 October 2010, D3= 22 October 2010, D4= 1 November 2010). It was shown that seed yield and yield components decreased by postponing the sowing date and water stress. Water stress at flowering stage had the most negative effect on these traits. Study of interaction effects of D × I on assessed traits revealed that the highest and lowest means were obtained in D1I1 and D4I2, respectively. Postponing the sowing date in all irrigation regimes decrease assessed traits, and flowering stage was the most sensitive stage to water stress in all sowing dates. The highest seed yield obtained in D1I1 by average is 3875 kg/ha.   Key words: Turnip rape (Brassica campestris L.), sowing date, irrigation regimes, yield, yield components.