Verification of Reference Evapotranspiration Estimated by Weighable Lysimeters and Its Applicability

The reference evapotranspiration (ET 0 ) is an essential indicator in explaining the water movement in the environment.In this study, we carried out to investigate the ET 0 , which were LYET (reference evapotranspiration calculated by the weighable lysimeter), PMET (reference evapotranspiration calculated by the FAO Penman-Monteith equation), and HSET (reference evapotranspiration calculated by the Hargreaves equation), respectively, and to estimate the relationship among the LYET, PMET, and HSET by regression analysis.Turfgrass was selected as the reference crop for calculating the ET 0 by the lysimeters.The experiment period was from 1st June to 31st December in 2015.The ET 0 in the lysimeter study area (National Institute of Agricultural Sciences, Wanju; WJ) was compared with that in the nearby Jeonju (JJ) location because of similar weather conditions.The relationship between PMET-WJ and PMET-JJ has the slope of 1.138, the coefficient of determination (R 2 ) of 0.972, and the relationship between HSET-WJ and HSET-JJ has a slope of 0.934 (R 2 =0.984); thus the fitness was high in both cases.The relationship between LYET and PMET in both soils (fine loamy, FL; coarse loamy, CL) showed a relatively high R 2 as higher than 0.9, whereas the relationship between LYET and HSET showed relatively low fitness (0.676 -0.736 of R 2 ).According to the month, the fitness of PMET:LYET was higher than that of HSET:LYET, and in November and December, the R 2 of PMET:LYET was lowered to 0.7 or less as turfgrass entered into a dormant stage.The LYET, PMET, and HSET were found to have significantly high positive correlations with the minimum temperature, maximum temperature, mean temperature, and solar radiation (p < 0.01) and a significantly high negative correlation with mean humidity (p < 0.01).The estimated ET 0 by the lysimeter experiment was evaluated to be highly conformable with the ET 0 calculated by the FAO PM equations.Follow-up studies such as long-term monitoring are necessary to cope with the changing climate every year.