No abstract

No abstract

No abstract

Daily crop water uptake was simulated using algorithms from three crop simulation models, CropSyst, CERES, and EPIC (listed in order of decreasing process detail). Simulated results were compared with measurements of sap flow and soil water content for maize (Zea mays L.) growing at Prosser, WA, under a wet and a dry irrigation treatment, and with soil water content measurements for nonirrigated maize at Davis, CA. At Prosser, the dry treatment imposed only a mild stress; at Davis, the stress was severe. Simulation variables such as maximum crop evapotranspiration, root density by soil layer, and green leaf area index were provided as daily input. At Prosser, all algorithms performed similarly when simulating crop water uptake. For the wet treatment, the root mean square error (RMSE) was 0.27 to 0.28 mm d−1, and the relative error [RE = 100 (RMSE/Measured average)] was 7.0 to 7.2%. For the dry treatment, simulation accuracy decreased (RMSE = 0.33–0.38 mm d−1; RE = 9.0–10.5%). The time evolution of water uptake simulated by CropSyst better depicted the measured sap flow (water uptake) difference between wet and dry treatments. Simulations of soil water content by layer for the wet treatment, compared with measurements available for 17 d, yielded RMSEs from 0.022 to 0.024 m3 m−3 and REs from 8.5 to 9.2%. For the dry treatment (12 d of measurements), the best simulations were obtained with the water uptake algorithms from CropSyst and CERES, with RMSE = 0.015 m3 m−3 (both models) and RE = 6.4% (CropSyst) and 6.6% (CERES), compared with RMSE = 0.019 m3 m−3 and RE = 8.1% for EPIC. Under the severe water stress at Davis, CropSyst had the best performance. This algorithm simulated changes in soil water content by layer (8 d of measurements available) with RMSE of 0.011 m3 m−3 and RE of 5.0%, while the RMSE and RE values for CERES and EPIC were 0.016 and 0.019 m3 m−3 and 7.6 and 9.0%, respectively. The more process‐oriented algorithm (CropSyst) showed an increasing advantage as water stress severity increased. The EPIC algorithm had the poorest performance under water stress. This could be improved by modifying the value of the water extraction distribution parameter in EPIC, but with this change the wet treatment simulations at Prosser deteriorated substantially, indicative of limitations in EPIC'S simple approach.

No abstract

No abstract

No abstract

RESUMO: Em duas zonas de latitudes similares e com diferentes altitudes, tais como Portoviejo (Região Costa) e Riobamba (Região Andina) no Equador, procurou-se ajustar os modelos de Holdridge (Ho) e Hargreaves-Samani (H-S) e com três modificações (modelos com constantes C HO e KE e KT Diário, Mensal e Anual, respectivamente) com o propósito de estimar a evapotranspiração de referência (ETo), em diferentes níveis das médias móveis do tempo, para o período de três dias. Uma vez ajustados os coeficientes C HO , KE e KT, estimou-se a ETo e foram validados os resultados mediante comparação com as mensurações da ETo, utilizando-se da evaporação do tanque Classe A com seu respectivo coeficiente (ETo Pan). Nos coeficientes C HO (Ho) e KE (H-S), o melhor desempenho foi obtido pela correlação do C HO e KS com o déficit da pressão de vapor (DPV), uma vez que o mesmo corrige o gradiente térmico vertical e incrementa a qualidade da predição da ETo, enquanto correlaciona o coeficiente KT (H-S) com a temperatura do ar, permitindo corrigir a radiação solar. Na comparação das três modificações de ambos os modelos com o ETo Pan, os modelos C HO Diário e H-S Mensal conseguiu-se as melhores estimativas da ETo com os indicadores de ajustes levemente melhores em Portoviejo e Riobamba. Finalmente, a qualidade das estimativas da ETo com três modificações de ambos os modelos é melhor em comparação com aquelas do modelo da Penman-Monteith para ambas as localidades.PALAVRAS-CHAVE: evapotranspiração de referência (ETo), altitude, temperatura, déficit de pressão de vapor, Hargreaves-Samani. ESTIMATION OF CROP REFERENCE EVAPOTRANSPIRATION FOR TWO LOCATIONS (COASTAL AND ANDEAN REGION) OF ECUADOR ABSTRACT:In two locations of Ecuador with similar latitude but different altitude (Portoviejo, Coastal zone and Riobamba, Andean zone) the Holdrigde (Ho) and Hargreaves-Samani (H-S) models and three modifications of these (daily, monthly and annual with constants C HO and KE and KT, respectively) were fitted in order to estimate crop reference evapotranspiration (ETo) for a range of moving averages in time, for a three day period. Once C HO , KE and KT were calibrated those ETo estimates were compared with ETo estimated by the Pan Evaporation Method (ETo Pan). Among C HO (Ho) and KE (H-S) coefficients, the best performance was achieved relating C HO and KE to vapor pressure deficit, since it corrected the vertical thermal gradient and increased the precision in ETo prediction, while relating the KT (H-S) coefficient to air temperature allowed the correction of the solar radiation. When comparing the three modifications of both models with ETo Pan, the daily C HO model and the monthly H-S model generated slightly better ETo estimates in Portoviejo and Riobamba, respectively. Finally, in terms of quality of ETo estimates, any of the three modifications of both models were better than those with Penman-Monteith in both locations.