Studies on Crop Coefficient of Soybean in Guanzhong Region of Shaanxi Province

Crop coefficient-reference crop evapotranspiration method is a popular method to calculate water requirement of crop.As an important parameter for this method,ascertained crop coefficient has become a key issue to study water requirement of crop.According to the field experiments from 2005 to 2007,reference crop evapotranspiration in Guanzhong region was calculated by using Penman-Monteith equation and actual crop evapotranspiration was achieved by water balance equation and adjustment coefficient of soil water.Crop coefficients of soybean in different stages were calculated based on the above results.Variations of crop coefficient were also analyzed.The results indicated that average reference crop evapotranspiration during crop growing stage in Guanzhong region is 498.4 mm.Average crop coefficient for the whole growing period is 0.89.The highest value 1.26 occured at the stage from flowering to fructification,followed by the stage from fructification to maturity with the average value of 1.04 and the lowest value 0.29 is at the stage between seeding to seedling.Under the climate background of Guanzhong region,there is a better relationship among soybean crop coefficient and cumulative temperature above 10℃.