Determination of daily evaporation and evapotranspiration of winter wheat and maize by large-scale weighing lysimeter and micro-lysimeter

Daily evapotranspiration of irrigated winter wheat (Triticum aestivum L.) and maize (Zea mays L.) were determined for five seasons between 1995 and 2000 using a large-scale weighing lysimeter, and soil evaporation for each crop was measured for one season using two micro-lysimeters at Luancheng Station in the North China Plain. The results showed that total water consumption averaged 453 and 423 mm for winter wheat and maize grown without water deficit. The water consumption of winter wheat during its growth period greatly exceeds the precipitation, which ranges from 50 mm in dry years to 150 mm in wet years. Consequently, supplemental irrigation is very important to winter wheat production in the region. The average crop coefficient during the whole growth period was 0.93 for winter wheat and 1.1 for maize. Evaporation from the soil surface took up 29.7 and 30.3% of the total evapotranspiration for winter wheat and maize, respectively, equaling an annual loss of more than 250 mm water. Thus, reducing soil evaporation could be one of the most important water-saving measures in this serious water deficit region. Leaf area index (LAI) and moisture in the surface soil greatly affect the ratio of soil evaporation to total evapotranspiration. The relationship between this ratio and surface soil moisture and leaf area index was established, and can help to improve field water utilization efficiency.