Long term simulation of water potential productivity of alfalfa on rain-fed highland in south of Loess Plateau

The water potential productivity of alfalfa on rain fed highland in south of loess plateau was simulated for long term(30 years) using EPIC model.Simulated results show that: the character of precipitation variation law simulated by using weather model in EPIC for 30-year and measured for 13-years is alike.The average precipitation deviation between 30-year simulated and 13-year really measured is 1.53%,the S-deviation is 1.86%,CV-deviation is 1.99%;The simulated water potential productivity fluctuates between 2.018～(17.521) t/hm~2,the average value is 7.7 t/hm~2.The average water stress day is only 10.2 days yearly,the water potential productivity is high and steady-going during first 5-years.During the last 25 years the water stress day increases to 123.1days,and water potential productivity reduced and changed with precipitation annually.The study of long-term simulation of water potential productivity for alfalfa shows that the precipitation of study area can't satisfy water request for high productivity.