Relationship between crop coefficient and precipitation pattern in the piedmont of Mt. Taihang

Based on the meteorological data and evapotranspiration (ET) of winter wheat and maize monitored by weighting lysimeter from 1995 to 2001 in Luancheng Experimental Station of Chinese Academy of Sciences, the relationship between crop coefficient and precipitation pattern was analyzed by reference crop method. In wheat season, the difference of crop coefficient was not significant in wet, dry and normal years, and the average value was 0.90 from 1995 to 2001. In corn season, the crop coefficient was higher in wet year (the average value was 1.2), but the difference of crop coefficient was insignificant in dry and normal years (the average value was 0.94). In order to appraise crop ET accurately and to conduct irrigation precisely, it is suggested that crop coefficient should be determined by long serial data covering wet, dry and normal years, especially in corn season.