Estimating Evapotranspiration of an Apple Orchard Using a Remote Sensing-Based Soil Water Balance

The main goal of this research was to estimate the actual evapotranspiration (ETc) of a drip-irrigated apple orchard located in the semi-arid region of Talca Valley (Chile) using a remote sensing-based soil water balance model. The methodology to estimate ETc is a modified version of the Food and Agriculture Organization of the United Nations (FAO) dual crop coefficient approach, in which the basal crop coefficient (Kcb) was derived from the soil adjusted vegetation index (SAVI) calculated from satellite images and incorporated into a daily soil water balance in the root zone. A linear relationship between the Kcb and SAVI was developed for the apple orchard Kcb = 1.82 SAVI 0.07 (R2 = 0.95). The methodology was applied during two growing seasons (2010–2011 and 2012–2013), and ETc was evaluated using latent heat fluxes (LE) from an eddy covariance system. The results indicate that the remote sensing-based soil water balance estimated ETc reasonably well over two growing seasons. The root mean square error (RMSE) between the measured and simulated ETc values during 2010–2011 and 2012–2013 were, respectively, 0.78 and 0.74 mm day1, which mean a relative error of 25%. The index of agreement (d) values were, respectively, 0.73 and 0.90. In addition, the weekly ETc showed better agreement. The proposed methodology could be considered as a useful tool for scheduling irrigation and driving the estimation of water requirements over large areas for apple orchards

Definición de la etapa de desarrollo de los cultivos para estimar evapotranspiración usando la metodología FAO-56 y sensores remotos

Se analizan los patrones temporales de variables biofísicas y espectrales: índicede área foliar (IAF), cobertura aérea (fv), e índice de vegetación cinemáticamentemodificado y ajustado por suelo (IV_CIMAS), en cultivos con densidad foliar alta(sorgo) y densidad foliar media (algodón y maíz). En el caso del sorgo, se analiza larelación de estos patrones temporales con el coeficiente basal de cultivo (Kcb). Lasvariables fv, IAF e IV_CIMAS fueron modeladas con un modelo expo-lineal truncado(ELT) y uno expo-lineal asimétrico (ELA). Ambos presentaron un buen ajusteestadístico en los tres cultivos; sin embargo, el modelo ELT resulta más adecuado,porque no requiere el valor máximo de la variable. De las tres variables modeladas,el IV_CIMAS representa mejor la cantidad y calidad de la vegetación en un píxel oparcela, ya que es función de la cantidad de área foliar, de su distribución espacial,de las propiedades ópticas de las hojas y del suelo de fondo de la vegetación. Con elobjeto de estimar evapotranspiración, según lo establecido en FAO-56, se analizarontres métodos distintos para caracterizar la etapa de desarrollo del cultivo de sorgo.Los métodos definen la duración de la etapa con base en la cobertura del suelo, laetapa de floración y mediante la información espectral (IV_CIMAS). Se analizaronlos errores (RECM y ERM) de las estimaciones de Kcb de la etapa de desarrollovegetativo mediante los tres métodos, en relación con las estimaciones de Kcb de unlisímetro de pesada, obteniendo los mejores resultados para el método IV_CIMAS ylos peores para el método FAO-56-Floración

Alcances y limitaciones del uso de índices espectrales de la vegetación para la estimación de la evapotranspiración y biomasa en cultivos con diferentes densidades de follaje

En el presente trabajo fueron revisados los alcances y limitaciones de los índices espectrales de la vegetación (IV) como herramienta para estimar evapotranspiración y biomasa en cultivos con diferente densidad foliar (media: algodón, maíz, trigo y alta: sorgo). Las relaciones entre las variables biofísicas y espectrales se analizaron dentro del marco teórico de las líneas de igual vegetación (iso-IAF) en el espacio rojo-infra rojo cercano, mediante IV (NDVIcp e IV_CIMAS) basados en la pendiente (b0) de las líneas iso-IAF. El problema de rápida saturación de sus bandas evidencia sus limitaciones en cultivos con alta densidad de follaje. Como alternativa se exploró el uso de una constante aditiva (a0). La relación entre a0 y la fracción de cobertura (fv) fue bi-lineal para ambas densidades de follaje, permitiendo una parametrización fácil en campo de los índices de vegetación, mientras que con biomasa presentó problemas en la definición de sus transiciones. Para estimar la evapotranspiración del sorgo (alta densidad) en función del coeficiente basal del cultivo (Kcb, método FAO-56) se analizaron los patrones temporales de las variables biofísicas y espectrales y sus transiciones con los Kcb. En este caso, se analizaron tres métodos para caracterizar la etapa de desarrollo del cultivo, dos establecidos por FAO-56 (cobertura y floración) y uno usando información espectral (IV_CIMAS). Los mejores resultados comparados con los Kcb de lisimetría se obtuvieron con el IV_CIMAS (RECM=0.017). En maíz y trigo (densidad media), para parametrizar el inicio y final de las etapas del Kcb de acuerdo a FAO-56, es necesario usar la fv y el índice de área foliar (IAF) para reflejar la geometría de siembra de los cultivos. Mediante el IV_CIMAS y estimaciones directas de las pendientes de las líneas iso-IAF, se obtuvieron relaciones lineales entre el Kcb y el IV_CIMAS para la etapa vegetativa y la de senescencia.____________In the present work the strengths and weaknesses of the spectral vegetation indices (VI) as a tool to evaluated evapotranspiration process and biomass production in crops with different foliage density (i.e. medium density: cotton, maize, wheat and high density: sorghum) were reviewed. The relations between the biophysics and spectral variables were analyzed within the theoretical frame of the equal leaf area index (iso-LAI) in the red-near infra red spectrum (R-IRC), through the based on the slope (b0) vegetation indices (NDVIcp and IV_CIMAS). The fast band saturation demonstrates their limitations to be used in high leaf density crops. Alternatively the use of the intercept (a0) was explored. The relationship between a0 and the cover fraction (fv) showed a bi-linear tendency for both leaf densities, allowing an easy parameterization of the vegetation indices in the field, while biomass showed problems in the definition of its transitions. In order to estimate high leaf density crop evapotranspiration using the crop basal coefficient (Kcb) (FAO-56 approach) the time patterns of the biophysic and spectral variables and their transitions with the crop coefficients (Kc) were analyzed. In this case, three methods were analyzed to characterize the crop development stage, two established in FAO-56 (cover and flowering) and one using the spectral information (IV_CIMAS). The best results in relation to Kcb estimations by lysimeter were obtained with IV_CIMAS (RECM=0.017). In maize and wheat, to parameterize the beginning and the end of the Kc stages according to FAO-56, it is necessary the use of both fv and the leaf area index (LAI) to show the crop sowing geometry. Linear relations between the Kcb and the IV_CIMAS for the vegetative and senescence stage were obtained using the IV_CIMAS and direct estimations of the iso-IAF lines slopes in medium leaf density crops.Tesis ( Doctorado en Ciencias, especialista en Hidrociencias).-Colegio de Postgraduados, 2009.CONACY

Irrigation Performance Assessment in Table Grape Using the Reflectance-Based Crop Coefficient

In this paper, we present the results of our study on the operational application of the reflectance-based crop coefficient for assessing table grape irrigation requirements. The methodology was applied to provide irrigation advice and to assess the irrigation performance. The net irrigation water requirements (NIWR) simulated using the reflectance-based basal crop coefficient were provided to the farmer during the growing season and compared with the actual irrigation volumes applied. Two treatments were implemented in the field, increasing and reducing the irrigation doses by 25%, respectively, compared to the regular management. The experiment was carried out in a commercial orchard during three consecutive growing seasons in Northern Chile. The NIWR based on the model was approximately 900 mm per season for the orchard at tree maturity. The experimental results demonstrate that the regular irrigation applied covered only 76% of the NIWR for the whole season, and the analysis of monthly and weekly accumulated values indicates several periods of water shortage. The regular management system tended to underestimate the water requirements from October to January and overestimate the water requirements after harvest from February to April. The level of the deficit of water was quantified using such plant physiological parameters as stem water potential, vegetative development (coverage), and fruit productivity. The estimated NIWR was roughly covered in the treatment where the irrigation dose was increased, and the analyses of the crop production and fruit quality point to the relative advantage of this treatment. Finally, we conclude that the proposed approach allows the analysis of irrigation performance on the scale of commercial fields. These analytic capabilities are based on the well-demonstrated relationship of the crop evapotranspiration with the information provided by satellite images, and provide valuable information for irrigation management by identifying periods of water shortage and over-irrigation

Estimating Evapotranspiration of an Apple Orchard Using a Remote Sensing-Based Soil Water Balance

The main goal of this research was to estimate the actual evapotranspiration (ETc) of a drip-irrigated apple orchard located in the semi-arid region of Talca Valley (Chile) using a remote sensing-based soil water balance model. The methodology to estimate ETc is a modified version of the Food and Agriculture Organization of the United Nations (FAO) dual crop coefficient approach, in which the basal crop coefficient (Kcb) was derived from the soil adjusted vegetation index (SAVI) calculated from satellite images and incorporated into a daily soil water balance in the root zone. A linear relationship between the Kcb and SAVI was developed for the apple orchard Kcb = 1.82 SAVI 0.07 (R2 = 0.95). The methodology was applied during two growing seasons (2010–2011 and 2012–2013), and ETc was evaluated using latent heat fluxes (LE) from an eddy covariance system. The results indicate that the remote sensing-based soil water balance estimated ETc reasonably well over two growing seasons. The root mean square error (RMSE) between the measured and simulated ETc values during 2010–2011 and 2012–2013 were, respectively, 0.78 and 0.74 mm day1, which mean a relative error of 25%. The index of agreement (d) values were, respectively, 0.73 and 0.90. In addition, the weekly ETc showed better agreement. The proposed methodology could be considered as a useful tool for scheduling irrigation and driving the estimation of water requirements over large areas for apple orchards