Peach orchard evapotranspiration in a sandy soil: Comparison between eddy covariance measurements and estimates by the FAO 56 approach |
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| Institution: | 1. Dept. of Civil and Enviornmental Engineering, Colorado State University, Fort Collins, CO 80523, USA;2. Aqua Engineering Inc., Fort Collins, CO 80525, USA;3. USDA-ARS, Water Management Systems Research Unit, Fort Collins, CO 80526, USA;1. Centro de Investigação em Agronomia, Alimentos, Ambiente e Paisagem (LEAF), Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal;2. Departamento de Producción Agraria, ETSIAAB, Universidad Politécnica de Madrid, UPM, Avd. Puerta de Hierro, 2, Madrid 28040, Spain;1. CEER Biosystems Engineering, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal;2. Centro de Investigação em Ciências Geo-Espaciais (CICGE), Rua do Campo Alegre, 4169-007 Porto, Portugal;3. Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal;4. INIAV I.P., Dois Portos, Portugal;5. Instituto de Ciências Agrárias e Ambientais Mediterrânicas (ICAAM), Universidade de Évora, Largo dos Colegiais, Évora, Portugal;1. USDA-ARS, Crop Production Systems Research Unit, Stoneville, MS 38776, United States;2. USDA-ARS, Forage and Livestock Production Research Unit, El Reno, OK 73036, United States;1. LMME, Faculté des Sciences Semlalia, Université Cadi Ayyad, Marrakech, Morocco;2. CESBIO, Université de Toulouse, IRD/UPS/CNRS/CNES, Toulouse, France;3. LP2M2E, Département de Physique Appliquée, Faculté des Sciences et Techniques, Université Cadi Ayyad, Marrakech, Morocco;4. Equipe de Mathématique et Traitement de l’Information (MTI), Ecole Nationale des Sciences Appliquées, Université Cadi Ayyad, Safi, Morocco;5. LabFerrer, Centro de asesoria Dr Ferrer, Cervera, Spain |
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| Abstract: | The evapotranspiration from a 3 to 4 years old drip irrigated peach orchard, located in central Portugal, was measured using the eddy covariance technique during two irrigation seasons, allowing the determination of crop coefficients. These crop coefficient values differed from those tabled in FAO Irrigation and Drainage Paper 56. In order to improve evapotranspiration estimates obtained from FAO tabled crop coefficients, a dual crop coefficient methodology was adopted, following the same guidelines. This approach includes a separation between the plant and soil components of the crop coefficient as well as an adjustment for the sparse nature of the vegetation. Soil evaporation was measured with microlysimeters and compared with soil evaporation estimates obtained by the FAO 56 approach. The FAO 56 method, using the dual crop coefficient methodology, was also found to overestimate crop evapotranspiration. During 2 consecutive years, measured and estimated crop coefficients were around 0.5 and 0.7, respectively. The estimated and measured soil evaporation components of the crop coefficient were similar. Therefore, the overestimation in evapotranspiration seems to result from an incorrect estimate of the plant transpiration component of the crop coefficient. A modified parameter to estimate plant transpiration for young, yet attaining full production, drip irrigated orchards is proposed based on field measurements. The method decreases the value of basal crop coefficient for fully developed vegetation. As a result, estimates of evapotranspiration were greatly improved. Therefore, the new approach seems adequate to estimate basal crop coefficients for orchards attaining maturity established on sandy soils and possibly for other sparse crops under drip irrigation conditions. |
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