Study of evapotranspiration and evaporation beneath the canopy in a buckwheat field

The determination of evaporation and transpiration separately is very important in improving water use efficiency and developing exact irrigation scheduling. Hourly crop evapotranspiration (ET (c)) and soil evaporation (E (g)) beneath the buckwheat canopy were measured using Bowen ratio energy balance method and micro-lysimeters, respectively. The total ET (c) and E (g) in the whole growth season of buckwheat were 187.4 and 72.1 mm, respectively. Crop coefficient of buckwheat plant was simulated by days after sowing (DAS) and leaf area index (LAI), the average values for four growth stages were 0.58, 0.59, 1.10, and 0.74; and soil evaporation coefficient (the ratio of soil evaporation to reference evapotranspiration) was modeled by soil water content at 5-cm depth by dividing the LAI into two stages. The relationship between the ratio of soil evaporation to actual evapotranspiration (E (g)/ET (c)) and LAI was decided. It was found that E (g)/ET (c) decreased from 1 to 0.3 with the increase in LAI.