The ratio of transpiration to evapotranspiration in a rainfed maize field on the Loess Plateau of China

Maize (Zea mays L.) is a major crop on the Loess Plateau, and calculating the ratio of transpiration to evapotranspiration (T/ET) of maize is important for estimating field water balance. In this study, the sap flow method was adopted to measure transpiration (T) characteristics of maize. In order to calibrate the sap flow gauge, the sap flow rate was compared to the leaf T determined by the weighing method. The sap flow value was measured per hour for 3 days and the mean of the hourly values for each day was taken as the daily value to avoid the influence of hydraulic capacitance. There was a significant linear relationship between leaf T and sap flow rate. The slope and intercept of linear regression were 0.764 and 4.944, with an R2 of 0.97 (p < 0.01). We also analyzed the T and ET of maize under field conditions. The T/ET of maize was 63.3% from July to September 2012. The T/ET and leaf area index had a good linear relationship. Partitioning of ET into soil evaporation (E) and T may have important implications for analyzing crop water use efficiency, evaluating the crop production potential of precipitation and optimizing field water management.