Abstract: crop coefficient approach presented in FAO-56,this paper estimated the available energy partitioned into two sources,canopy and soil surface (A_c and A_s),and the latent and sensible heat fluxes,λE_c,λE_s,H_c and H_s.The results showed that under non-water stress condition,the interaction between H_c and λE_c made canopy absorbed a micro-advection to enhance transpiration expressed by latent heat flux,with the value of (λE_cⁱ-A_cⁱ).The greatest enhancement of transpiration occurred at the crop development stage with leaf area index between 0.6 and 2.4,and the average of the enhancement was 4.32 MJ·m^-2·d^-1.Soil evaporation was in progress with a rate below the available energy of soil,due to the interaction between H_c and λE_c under non-water stress condition,except a few days immediately after heavy rain.The evaporation rate depended on the percentage of soil available energy dissipated as latent heat flux.The average value of minimum percentage,11.5%,occurred at mid-season stage,while that of maximum percentages,51.9%,occurred at initial stage.Latent heat fluxes were the important components of energy exchange during the process of evapotranspiration.The available energy dissipated as latent heat fluxes of the two sources during crop development,mid-season,and late season stages accounted for over 83% of the total energy.

Key words: Rare earth elements, Crop, Relative seedling ratio, LC₅₀