Abstract: To optimize sowing date for high yield and quality forage rape in North China Plain, 4 Brassica napus varieties and 4 sowing dates were used to study the temperature effects. Results showed that by delayed sowing date, both average temperature and effective accumulative temperature were increased during forage rape growth, and the initial flowering days became earlier with prolonged blooming periods and shortened growth periods (by 2-7 d). The forage yield was more than 35 t/hm2 under early sowing date (before March 28), and was decreased by delayed sowing. Forage yields were significant different between varieties, and Huayouza 62 was the highest (p<0.01). Significantly negative correlation was found between forage yield, forage quality and fiber content. The effective accumulative temperature during seeding period played significantly negative role on neutral detergent fiber. Vegetative and post-flowering growth periods played significantly positive roles on neutral detergnnt fiber. Therefore, high yield and high quality rape production in North China Plain should be obtained by using Huayouza 62 and sowing between March 8 to 18. The forage yield could reach 50 t/hm2 with high crude protein, starch, carbohydrate and total digestible nutrient.

Key words: forage rape (Brassica napus L.), temperature, sowing date, forage yield, forage quality