Evaluation Of Evapotranspiration Models Using Lysimeter Measurement:case Of Awash Melkassa, Ethiopia

Abstract

Crops Require Adequate Water In The Soil To Maintain The Plant Growth, Production And Productivity. Correct Estimation Of Crop Evapotranspiration Depends On The Correct Estimation Of Reference Evapotranspiration. A Study Was Undertaken At Research Farm Of Melkassa Agricultural Research Center Of The Ethiopian Institute Of Agricultural Research With The Objective Of Determining Crop Water Requirement And Crop Coefficient For Alfalfa And Calibrate The Most Commonly Used Estimation Models Under Melkassa Climatic Condition. Field Study Was Undertaken Using Two Drainage Types Of Lysimeters That Involved The Various Components Of The Water Balance Equation In Determining Crop Water Requirement Of Alfalfa. On The Basis Of Measured Alfalfa Crop Evapotranspiration Four Commonly Used Eto Estimation Model, Viz., Penman-Monteith, Hargraves-Samani, Turc And Makkink Were Calibrated And Evaluated To Obtain Best Fit Model Under Melkassa Climatic Condition. The Root Mean Square Error, Index Of Agreement And Coefficient Of Residual Mass Were Used For Evaluating Prediction Models. The Result Indicated The Total Crop Water Requirement Of Alfalfa Under Melkassa Climatic Condition Was 310.29 Mm Per One Cutting Period And The Maximum Alfalfa Crop Evapotranspiration Was 6.92 Mm Day-1 And The Mean Crop Coefficient At The Different Crop Growth Stages, Viz., Initial, Development, Mid And Late Season Were 0.46, 0.8, 1.24 And 1.12, Respectively. Evaluation Of The Four Modeld Has Indicated That Turc And Makkink Models Had Unsatisfactory And Poor Performance Without Calibration And Hargreaves??Samani Model Proved To Be Performing Better Than Turc And Makkink Model. The Makkink Model Was Performed The Least Among Other Model With Rmse = 1.94 Mm Day-1, I = 0.087 And Crm = 30% Based On Estimation Of Actual Alfalfa Et. The Fao Penman- Monteith Had Been Found To Be Most Precise For Estimating Eto With Rmse = 0.9 Mm Day-1, I = 0.6 And Only Crm = 10% Based On Estimation Of Actual Alfalfa Et.