Experimental Study on Crop Coefficient of Maize in Guanzhong Region of Shaanxi Province

According to the meteorological data between the year 1999 to 2003 of Guanzhong Region in Shaanxi province,the reference crop evapotranspiration of summer maize during various growing periods is calculated out by adopting the formula of Penman-Monteith.With the comparison to the data obtained through large-scale weighing lysimeter,the variation of the crop coefficient of different growing periods is analyzed.The result implies that the average reference crop evapetranspiration during crop growing stage in Guanzhong region is 346.87 mm,while the actual crop evapetranspiration is 350.86 mm.The summit of the crop coefficient is observed in the whole growth period,which is 1.27 and appears in the heading-filling period.At the same time,there are good third-order polynomial and second-order polynomial relations between Kc and the days after planting and the cumulative temperature above 10 ℃,respectively.