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The evapotranspiration ( E T ) process is an essential component in many agricultural water management systems, and its estimation is even more determinant when crops are grown under water-limited environments. The traditional canopy resistance ( r c ) approaches were evaluated to simulate potato evapotranspiration ( E T c p ) using the original Penman–Monteith equation under different irrigation levels. A field study was carried out on a drip-irrigated potato crop (var. Puyehue INIA) located in the Research Center Carillanca (INIA), La Araucanía Region, Chile (38°41′ S, 72°24′ W, 188 m above sea level) during the 2018/2019 and 2019/2020 growing seasons. The different irrigation levels were full irrigation ( I L 1 ), 75% of I L 1 ( I L 2 ), and 60% of I L 1 ( I L 3 ). The soil water content, morphological, physiological, meteorological, and micrometeorological variables were measured to calculate the different r c approaches and estimate ET for both growing evaluated seasons. The final values of estimated E T c p were compared to the soil water balance method ( E T c p W B ). The use of amphistomatous (LA) and hypostomatous (LH) r c approaches are the best alternative to estimate the E T c p on potato crops. The best estimation of ET was found for E T c p L A with an overestimation of 0.6% for I L 1 , 7.0% for I L 2 , and 13.0% for I L 3 , while for E T c p L H with underestimations of 12.0, 11.0 and 31.0% for I L 1 , I L 2 , and I L 3 , respectively. The lowest average values of root mean square error (RMSE), mean absolute error (MAE), and index of agreement (d) were observed for E T c p L A in both I L 1 and I L 2 conditions, with values of 4.4 and 3.2 mm, 3.2 and 2.5 mm, and 0.82 and 0.87, respectively. More investigation is necessary on the plasticity of the morphological features of potato leaves and canopy geometry, as the stomatal water vapor flowing on the canopy surface could be affected, which is a key factor in the canopy resistance model for accurate E T estimation under soil-water-limited conditions. [ABSTRACT FROM AUTHOR]

The aim of this research was to evaluate the clumped model for estimating latent heat flux (LE) and actual evapotranspiration (ETa) over a non-water-stressed olive orchard. Additionally, submodels to compute the net radiation Rn, soil heat flux G, and canopy resistance were also included. For this objective, a database was used from an experimental unit inside a commercial superintensive drip-irrigated olive orchard located in the Pencahue Valley, Maule Region, Chile (35°23′S, 71°44′W; 96 m above sea level) during the 2009/10 and 2010/11 growing seasons. The evaluation was carried out using measurements of LE obtained from an eddy covariance (EC) system. In addition, estimated values of Rn, G, and were compared with ground-truth measurements from a four-way net radiometer, soil heat flux plates with soil thermocouples, and a portable porometer, respectively. Results indicated that the clumped model underestimated LE and ETa with errors of 11.0% and 3.0%, respectively. Values of the root-mean-square error (RMSE), mean bias error (MBE), and index of agreement dr for LE were 35 W m−2, −1.0 W m−2, and 0.96, while those for ETa were 0.48 mm day−1, 0.04 mm day−1, and 0.64, respectively. The submodels computed Rn and G with errors less than 6% and RMSE values less than 65 W m−2, while the Jarvis-type model predicted with RMSE = 41 s m−1 and MBE = 7.0 s m−1. Finally, a sensitivity analysis indicated that the ETa estimated by the clumped model was significantly affected by variations of ±30% in the values of the LAI and the minimum stomatal resistance rstmin. [ABSTRACT FROM AUTHOR]

Reference evapotranspiration (ETo) has a key role in irrigation scheduling. In this sense, the Hargreaves-Samani equation (HS) is a reliable and widely used method to estimate ETo. The HS equation just requires temperature and solar radiation data, making it a suitable method for places that lack of wind speed and relative humidity information. However, literature shows that a local calibration of its empiric parameter is needed for its complete application. This work shows a calibration for the Maule region in central-southern Chile. For this purpose, the Penman-Monteith equation from FAO-56 (PM) was considered as a reference, using a network of 400 meteorological stations between the 32° and 39° of south latitude for the 1973-2011 period. The calibration was based on the computation of the ratio of ETo calculated by HS and PM and the spatial behaviour of input variables and parameters. The spatial distribution was done by geographical weighted regression and ordinary Kriging with a linear variogram, assisted by a digital elevation model from the Shuttle Radar Topography Mission and surface reflectances from Moderate Resolution Imaging Spectroradiometer. The process of calibration was validated with daily data through all months, with comparative errors of 5% against PM. [ABSTRACT FROM AUTHOR]

To evaluate the partitioning of net radiation ( R) and actual evapotranspiration ( ET), measurements of R, sensible heat flux ( H), soil heat flux ( G), latent heat flux ( LE), reference evapotranspiration ( ET), transpiration ( T) and soil evaporation ( E) were taken during the 2009/2010 and 2010/2011 growing seasons on a flat and uniform olive (cv. Arbequina) orchard, located in the Pencahue Valley, Región del Maule, Chile (35°23′ LS; 71°44′ LW; 96 m above sea level). Olive trees were trained on a triangular hedgerow system with a plant density of 1333 trees ha (superintensive). An eddy covariance system, sapflow sensors and microlysimeter were used to measure ET, T and E, respectively. Results indicated that the eddy covariance measurements showed a lack of the energy balance closure of 12.8 %. Values of LE, H and G were between 28-47, 34-68 and 2-6 % of R, respectively, while ratios of T and E to ET ranged between 0.64-0.74 and 0.26-0.36, respectively. During two growing seasons, the single crop coefficient ( K = ET/ ET) was between 0.27 and 0.66, while the dual crop coefficient ( T/ ET + E/ ET) ranged between 0.26 and 0.56. According to these results, H and T were the main component of R and ET, respectively, for the particular conditions of the drip-irrigated olive orchard with a fractional cover of 30 % and wetted area of 4.5 %. [ABSTRACT FROM AUTHOR]

The use of actual evapotranspiration (ETa) models requires an appropriate parameterization of the available energy, where the net radiation (Rn) is the most important component. Thus, a study was carried out to calibrate and evaluate three semiempirical approaches to estimate net radiation (Rn) over a drip-irrigated olive (Olea europaea L. 'Arbequina') orchard during 2009/2010 and 2010/2011 seasons. The orchard was planted in 2005 at high density in the Pencahue Valley, Maule Region, Chile. The evaluated models were calculated using the balance between long and short wave radiation. To achieve this objective it was assumed that Ts = Ta for Model 1, Ts = Tcv for Model 2 and Ts = Tr for Model 3 (Ts is surface temperature; Ta is air temperature; and Tcv is temperature inside of the tree canopy; Tr is radiometric temperature). For the three models, the Brutsaert's empirical coefficient (φ) was calibrated using incoming long wave radiation equation with the database of 2009/2010 season. Thus, the calibration indicated that φ was equal to 1.75. Using the database from 2010/2011 season, the validation indicated that the three models were able to predict the Rn at a 30-min interval with errors lower than 6%, root mean square error (RMSE) between 26 and 39 W m-2 and mean absolute error (MAE) between 20 and 31 W m-2. On daily time intervals, validation indicated that models presented errors, RMSE and MAE between 2% and 3%, 1.22-1.54 and 1.04-1.35 MJ m-2 d-1, respectively. The three Rn-Models would be evaluated and used in others Mediterranean conditions according to the availability of data to estimate net radiation over a drip-irrigated olive orchard planted at high density. [ABSTRACT FROM AUTHOR]

A two-layer model was evaluated to simulate latent heat flux (LE) and evapotranspiration (ET) of a drip-irrigated olive orchard during the 2009-2010 and 2010-2011 growing seasons. This orchard is located in the Pencahue Valley, Maule Region, Chile (35º 23'S; 71º 44'W; 96 m above mean sea level). A constant canopy size was maintained during the two study periods, with leaf area index (LAI) and fractional cover (fc) ranging between 1.29 and 1.34 m² m-2 and between 0.29 and 0.30, respectively. In addition, the olive orchard was maintained under non-water-stressed conditions, with a midday stem water potential greater than -1.96 MPa. The LE and ET obtained from the eddy covariance (EC) system were used to validate the performance of the two-layer model The validation including the two study periods indicated that mean values of root mean square error (RMSE) and index of agreement (Ia) for latent heat flux were 28 W m-2 and 0.98, respectively, while the RMSE and Ia values for olive evapotranspiration were 0.52 mm d¹ and 0.84, respectively. This study also indicated that the two-layer model overestimated LE and ET by about 2% and 6%, respectively. Finally, results indicated that the model was very sensitive to errors in the measurements of stomatal conductance and LAI. Major errors of the two-layer model to simulate ET directly were associated with very dry atmospheric conditions (vapor pressure deficit between 3.5 and 4.5 kPa) observed during the afternoon. However, the main errors did not significantly affect the overall performance of the two-layer model. [ABSTRACT FROM AUTHOR]