Research on the optimum time of fall cutting of alfalfa in Beijing plain

The influences of fall cutting and the cutting time on forage yield of the fall cutting, moisture content of forage, ratio of stem and leaf, regrowth height of alfalfa before winter, over wintering rate, yield of the first cutting in the next year of the Zhongmu 1 alfalfa(Medicago sativa) in Beijing plain were investigated. The results showed that before the killing frost, yield of the fall cutting increased gradually with the delay of the fall cutting time（P0.05）,but it decreased after the killing frost. Moisture content of forage kept constant before the first frost, increased gradually after the first frost, while decreased significantly after the killing frost（P0.05）. Ratio of stem and leaf increased significantly after the killing frost（P0.05）, regrowth height of alfalfa before winter decreased gradually with the delay of the cutting time before the killing frost, kept constant after the killing frost. An additional fall cutting and different cutting time had no significant effects on the over wintering rate of Zhongmu 1alfalfa. Yield of the first cutting in the next year increased gradually with the delay of the cutting time before the killing frost（P0.05）,the earliest cutting were significantly lower than control（P0.05）,the others before the killing frost were not significant compared with control. The preliminary conclusion showed that the fall cutting in Beijing plain was feasible, the fall cutting critical period of alfalfa in Beijing plain was the interval time between the last summer cutting and the fall cutting less than 8 weeks(5 ℃ available accumulated temperature 720 ℃), the interval time between the first killing frost and the fall cutting more than 3 weeks (5 ℃ available accumulated temperature90 ℃). The optimum fall cutting period of alfalfa in Beijing plain was 8-11 weeks of the interval time between the last summer cutting and the fall cutting (5 ℃ available accumulated temperature was 760-800 ℃), 0-3 weeks of the interval time between the first killing frost and the fall cutting (5 ℃available accumulated temperature was 0-40 ℃).