Hourly Grass Evapotranspiration in Modified Maritime Environment

Ortega-Farias, S.O. Facultad de Ciencias Agrarias, Escuela de Agronomia, Universidad de Talca, 747 Casilla, Talca, Chile.The Penman method using hourly and daily weather data was evaluated to estimate daily reference evapotranspiration over a well-established stand of Alta fescue under different atmospheric conditions. The performance of the Penman equation was evaluated using evapotranspiration measured by the Bowen ratio energy balance (BREB) method. Good agreement between the BREB method and Penman using hourly weather data was observed. On an hourly basis, the overall standard error of estimate (SEE) and absolute relative error (ARE) were 0.06 mms.h -1 (40.8 Ws.m -2 ) and 5.2%, respectively. On a daily basis, the SEE was 0.55 mms.d -1 and the ARE was 6.9%. The SEE and ARE for the Penman model using daily weather data were 0.74 mms.d -1 and 9.8%, respectively. These results suggest that the accuracy of the Penman equation could improve if hourly weather data were used as inputs and strongly suggest that the Penman equation with hourly weather data could be used in the Willamette Valley to predict daily evapotranspiration for irrigation purposes

Daytime variation of sensible heat flux estimated by the bulk aerodynamic method over a grass canopy

Ortega-Farias, S.O. Escuela de Agronomia, Facultad de Recursos Naturales, Unversidad de Talca, Casilla 747-Talca, ChileA study was performed to evaluate the bulk aerodynamic method for estimating daytime variation of sensible heat flux (HA) for a wetted and non-wetted grass canopy under clear and cloudy days. The aerodynamic resistance applied was corrected for atmospheric stability using the Oregon State University One-Dimensional Planetary Boundary Layer model stability function. The performance of the bulk aerodynamic method was tested with indirect measurements of sensible heat flux (HB) derived from the Bowen ratio energy balance method on 20-min time intervals. Results indicate that there was a good agreement between HB and HA with a coefficient of correlation of 0.93 and slope of the regression line through the origin of 0.96

Evaluation of the Penman-Monteith model for estimating soybean evapotranspiration

Ortega-Farias, S.O. Centro de Investigación y Transferencia en Riego y Agroclimatología (CITRA), Facultad de Ciencias Agrarias, Universidad de Talca, 747 Casilla, Talca, Chile

Latent heat flux over Cabernet Sauvignon vineyard using the Shuttleworth and Wallace model

Ortega-Farias, S.; Carrasco, M.; Olioso, A.; Acevedo, C. and Poblete,C. Centro de Investigación y Transferencia en Riego y Agroclimatologí­a (CITRA), Facultad de Ciencias Agrarias, Universidad de Talca, Casilla 747, Talca, Chile.The Shuttleworth and Wallace model (SW) was evaluated to estimate latent heat flux above a drip-irrigated Cabernet Sauvignon vineyard, located in the Pencahue Valley, Region del Maule, Chile (35°22′ LS; 71°47′ LW; 150 m above sea level). The performance of the WS model (LEws) was evaluated against the eddy-covariance method (LEed) on a 30 min time interval. Results indicate that the root mean square error (RMSE) and mean absolute error (MAE) were 29 W m−2 and 22 W m−2, respectively. For the vine evapotranspiration (ETv), RMSE was 0.42 mm day−1 and MAE was 0.36 mm day−1. The largest disagreements between LEed and LEws were observed under dry atmospheric conditions. Also, the sensitivity analysis indicates that predicted ETv by the SW model was sensitive to errors of ±30% in leaf area index and mean stomatal resistance, but it was not affected by errors in the estimation of aerodynamic resistances

Assessments CO2 assimilation on a per-leaf-area basis are related to total leaf area

Moreno, Yerko and Ortega-Farias, Samuel. Facultad de Ciencias Agrarias,University of Talca,Talca,Chile

Analysis of ratio-based responses

Moreno, Yerko and Ortega-Farias, Samuel. Facultad de Ciencias Agrarias,University of Talca,Talca,Chile

Estimativa do balanço de energia em cambarazal e pastagem no norte do Pantanal pelo método da razão de Bowen Estimate of energy balance in cambarazaland pasture in the north of Pantanal by Bowen ratio method

O estudo do balanço de energia de uma superfície vegetada e a atmosfera é importante para caracterizar o microclima local, identificar interações entre variáveis ambientais e a vegetação, e identificar efeitos das atividades antropogênicas. O objetivo deste trabalho foi estimar a variação sazonal do balanço de energia pelo método da razão de Bowen em uma área de vegetação monodominante de Cambará na RPPN SESC-Pantanal e uma área de pastagem na Fazenda Experimental da UFMT. Os componentes do balanço de energia apresentaram sazonalidade, com maiores médias na estação chuvosa nas duas áreas de estudo. No cambarazal houve maior variação do fluxo de calor latente da estação seca para a chuvosa que na pastagem. Entretanto, a variação sazonal do fluxo de calor sensível foi menor no cambarazal que na pastagem, devido ao efeito termo-regulador do cambarazal, em função da maior biomassa. A energia disponível aos dois sítios foi destinada prioritariamente em fluxo de calor latente, 80,0% no cambarazal e 56,6% na pastagem, seguido pelo fluxo de calor sensível, 19,1 e 42,9%, e pelo fluxo de calor no solo, 0,3 e 7,2%.<br>The energy balance study of a vegetated surface and atmosphere is important to characterize the local microclimate, identify interactions among environmental variables and the vegetation and to identify anthropogenic activities effects. The objective of this work was estimate the seasonality of energy balance by Bowen ratio method in a monodominant vegetation of Cambará area in the RPPN SESC-Pantanal and a pasture area in UFMT's Experimental Farm. The energy balance components presented seasonality, with larger averages at the rainy station in two areas of study. In the cambarazal was a higher variation of the latent heat flux of the dry season for the rainy season that in the pasture. However, the seasonal variation of the sensible heat flux in the cambarazal was lower than in the pasture, due to the thermo-regulatory effect in the cambarazal, according to the largest biomass. The available energy at two ranches was partitioned priority in latent heat flux, 80,0% in the cambarazal and 56,6% in the pasture, followed by the sensible heat flux, 19,1 and 42,9%, and by the soil heat flux, 0,3 and 7,2%