Characteristics Analysis of Temperature Change during Overwintering Period of Northward Winter Wheat in Irrigated Areas of Ningxia

Based on the daily temperature data of 1961-2009 of eleven meteorological stations in the Irrigated Areas of Ningxia,the change characteristics of the temperature indicators was analyzed.The results showed that the minimum temperature in January in 1961-2009 was with-19.8℃,it increased by 3.9% compared to the time period before the northward winter wheat growing;The average temperature in January was with-7.4℃,it increased by 12.8% compared to the time period before the northward winter wheat growing,the average temperature in January lower than-9℃decreased by 75%,this indicated that the Irrigated Areas of Ningxia had already belonged to the suitable growing areas within the northern boundary of winter wheat.The total accumulated temperature above zero degree in growth period of winter wheat was with 1969.6 ℃·d,it increased by 11.1% compared to the time period before the northward winter wheat growing,whereas it could ensure the normal growth of winter wheat whether before or after the northward winter wheat growing.The accumulated temperature above zero degree before overwintering period of winter wheat was with 363 ℃·d,it increased by 10.3% compared to the time period before the northward winter wheat growing,which was close to the minimal requirement for the accumulated temperature above zero degree before overwintering period of winter wheat in the Northern China Plain.The negative accumulated temperature in overwintering period of winter wheat was with-586 ℃·d,it increased by 22.3% compared to the time period before the northward winter wheat growing,but it could still not meet the minimal requirement for the safe overwintering of winterness and strong winterness varieties of winter wheat in the Northern China Plain.Early and timely sowing,enhancing the water and fertilizer managements were the key technical measures to ensure high yield of winter wheat which can increase the accumulated temperature above zero degree before overwintering period,breed strong seedlings and increase overwintering survival percentage.