Simulation of soil evaporation under different ground coverage with semi-empirical models

Minimizing soil evaporation is a key element in improving water use efficiency in dry areas. Experiments were conducted in the winter wheat field during 2004-2005 to compare effects of different row spacing on soil evaporation. A model to estimate soil evaporation was developed based on the experimental data. The reference crop evapotranspiration (ET0) was estimated by the Penman-Montieth equation, and the factors affecting evaporation under crop canopy were divided into both the radiation item (ETsl) and the aerodynamics item (ETs2) according to the degree of crop canopy coverage (f(c)). The simulation equation for actual evaporation, combining with soil moisture parameter, was established in this paper. In this study, a light meter was utilized to measure f(c), which replaced leaf are index (LAI) in evaporation estimation. In comparison with the measured evaporation by micro-lysimeters (ML) in four row spacing: 7.5 cm, 15 cm, 22.5 cm. and 30 cm, tested in a randomized block design, the simulated daily evaporation had root mean square errors, (RMSE) of 0.22 mm, 0.24 mm, 0.25 mm 0.26 mm and a bias of 0.01 mm, 0.02 mm, -0.08 mm, -0.03 mm respectively. Results showed that using canopy coverage factor to replace leaf area index could effectively estimate soil evaporation.