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Penman -Monteith formulation for direct estimation of maize evapotranspiration in well watered conditions with full canopy
An efficient use of water resources for irrigation requires an accurate estimation of crop water requirements. The traditional approach to estimate crop evapotranspiration (ET) requires the use of a crop coefficient and an estimate of a reference ET. However, crop coefficients depend on crop type, management, and weather conditions and they sometimes lead to large errors in crop ET estimates. The Penman-Monteith (PM) formulation can be used to estimate crop ET without using a crop coefficient if the crop surface and aerodynamic resistances are known. PM formulation application also requires weather measurements from above the crop in question; however, this is not possible in everyday applications. This study analyzed the feasibility of using the PM formulation in maize ET estimation and characterized the uncertainties introduced when the weather data are measured above grass. Expressions to estimate aerodynamic and canopy surface resistances were evaluated. Weather measurements from above the maize canopy and above grass were compared. Techniques to translate weather measurements from a nearby weather station with grass cover to a maize canopy were evaluated. Maize ET was estimated separately using measurements taken above the maize canopy and measurements taken above grass and translated to the maize canopy. Eddy covariance measured and estimated maize ET were compared. The results show that the PM formulation can be used to estimate the maize ET. The approach worked reasonably well for a full crop cover under well watered conditions. The critical point was to estimate the surface resistance as a function of climatic variables. Maize ET was estimated with RMSE values that varied between 0.3 and 0.78 mm/day when the ET was estimated using weather data measured above the maize canopy. The uncertainty introduced when the maize ET was estimated using weather data measured above the grass was relatively small, the RMSE increased between 0.12 and 0.2 mm/day. A different crop management system introduced larger ET estimation differences than the uncertainty introduced when the ET was estimated using weather data measured above the grass. ^
Agriculture, Agronomy|Engineering, Agricultural
Flores, Hector, "Penman -Monteith formulation for direct estimation of maize evapotranspiration in well watered conditions with full canopy" (2007). ETD collection for University of Nebraska - Lincoln. AAI3294284.