Growing Season Evapotranspiration and Crop Coefficient

by Esmaiel Malek,
Gail E. Bingham,



Document Type: Proceeding Paper

Part of: Management of Irrigation and Drainage Systems: Integrated Perspectives

Abstract: The Bowen ratio-energy balance (BREB) method was used to continuously estimate 20-minute actual evapotranspiration (ETa) in the middle of a 36-ha well-watered alfalfa field from 10 April to 5 October, 1992. Daily totals of ETa were compared with potential evapotranspiration (ETp) estimated using the modified Penman method. About 90% net radiation (Rn) was utilized for ETa, and the crop coefficient Kc = ETa/ETp was 79%. The crop coefficient occasionally was greater than unity. Regression analysis revealed that Rn = 0.560Rs - 1.317 with r = 0.933 and Rn = 0.556Rs - 0.830 with r = 0.959 for clear and clear-plus-cloudy sky conditions, respectively, during the season where solar radiation (Rs) and Rn are in MJ m-2. This BREB method is a promising tool for automated irrigation systems in remote areas.

Subject Headings: Crops | Solar radiation | Evapotranspiration | Regression analysis | Irrigation systems | Seasonal variations | Vegetation

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