Effect of sowing date and rate on canopy intercepted photo-synthetically active radiation and yield of winter wheat

Suitable sowing time of winter wheat is a key to full and strong development of young plants and high yield. Transmitted photo-synthetically active radiation (TPAR), leaf area index (LAI), intercepted photo-synthetically active radiation (IPAR) and yield of winter wheat differ with sowing date and sowing rate. Experiment results indicate that while LAI and TPAR decrease with late sowing date, IPAR, on the other hand, increases with late sowing date. IPAR and LAI have significantly positive correlation with a correlation coefficient of 0.756. However, IPAR and LAI have significantly negative correlation with a correlation coefficient of －0.872. Wheat yield decreases with the delayed sowing date. However, sowing seeds before October 20 minimizes differences in wheat yield with different sowing date. Yield is enhanced via rational postponement of sowing date of wheat. It as well extends development period of corn in winter wheat-summer corn crop rotation system.