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FAO-56 Dual Crop Coefficient Method for Estimating Evaporation from Soil and Application Extensions
Abstract
Crop coefficient curves provide simple, reproducible means to estimate crop evapotranspiration (ET) from weather-based reference ET values. The dual crop coefficient sKcd method of the Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) is intended to improve daily simulation of crop ET by considering separately the contribution of evaporation from soil. The dual method utilizes "basal" crop coefficients representing ET from crops having a dry soil surface and separately predicts evaporation from bare soil based on a water balance of the soil surface layer. Three extensions to the evaporation calculation procedure are described here that are intended to improve accuracy when applications warrant the extra complexity. The first extension uses parallel water balances representing the portion of the soil surface wetted by irrigation and precipitation together and the portion wetted by precipitation alone. The second extension uses three "stages" for surface drying and provides for application to deep cracking soils. The third extension predicts the extraction of the transpiration component from the soil surface layer. Sensitivity and analyses and illustrations indicate moderate sensitivity of daily calculated ET to application of the extensions. The dual Kc procedure, although relatively simple computationally and structurally, estimates daily ET as measured by lysimeter relatively well for periods of bare soil and partial and full vegetation cover.
... The following text provides a brief overview of the ET Demands model used to estimate potential crop ET (ETc), the net irrigation water requirement (NIWR), and effective precipitation (Prz). Detailed documentation of the ET Demands model is described in Allen et al. (2005), Allen and Robison (2009), Huntington et al. (2015) and Allen et al. (2020). Specifics related to the Python ET Demands software and application can be found at: https://github.com/WSWUP/et-demands. ...
... At the core of the ET Demands model is the FAO-56 dual crop coefficient model (Allen et al., 1998) that makes separate calculations for transpiration and evaporation from exposed soil (Figure 6). Use of a dual crop coefficient approach produces more accurate shortterm ET estimates (e.g., daily) than traditional single crop coefficient (Kc) methods by accounting for periodic wetting events such as precipitation or irrigation (Allen et al., 2005). The ETc for each crop type was estimated at each gridMET cell (i.e., ET cell) using the FAO-56 dual crop coefficient equation: ...
... The crop transpiration layer extends from the surface to each crop type's maximum rooting depth. Rooting depths within ET Demands are primarily derived from FAO-56 (Allen et al., 2005) and Allen and Robison (2007) with root growth estimation between initial and maximum depths based on Borg and Grimes (1986). ...
Agricultural consumptive use of irrigation water (CUirr) is over 60 percent of
consumptive water use in the Upper Colorado River Basin (UCRB). Historical
evapotranspiration (ET) estimates derived from theoretical potential rates and empirical methods often inaccurately represent actual water use under the region’s variable climate and water supply. Advancements in remote sensing of ET provide spatially and temporally continuous estimates of actual ET (ETa) at daily, field-scale resolution not possible with historical approaches. This study combines best available ET estimates from OpenET’s implementation of the Earth Engine Mapping EvapoTranspiration at high Resolution with Internalized Calibration (eeMETRIC) remote sensing ET model with effective precipitation (Prz) estimates from the crop
ET and daily soil water balance model, ET Demands, to produce updated historical ET and CUirr estimates for the UCRB from 1991-2022. Additionally, field-level maps of historical irrigation status were developed using remotely sensed indices of vegetation vigor and fraction of reference ET to spatially constrain CUirr volume estimates to actively irrigated lands on a yearly basis. Analysis workflows follow preferred approaches adopted by the Upper Colorado River Commission and Upper Division States for unified consumptive use estimation throughout the UCRB.
... Together with the measurement or estimation of the almond tree water requirements, studies have dealt with the derivation of single (K c ) and basal (K cb ) crop coefficients for young and mature almond trees, representing the ratios of the ET c and crop transpiration (T c ), respectively, to the grass reference evapotranspiration (ET o ), (i.e., K c = ET c /ET o and K cb = T c /ET o ; Allen et al. 1998;Pereira et al. 2024). These coefficients are an operative tool for farmers and technicians when irrigation scheduling is performed based on the daily crop water demand using the two step approach (Allen et al. 1998). ...
... Together with the measurement or estimation of the almond tree water requirements, studies have dealt with the derivation of single (K c ) and basal (K cb ) crop coefficients for young and mature almond trees, representing the ratios of the ET c and crop transpiration (T c ), respectively, to the grass reference evapotranspiration (ET o ), (i.e., K c = ET c /ET o and K cb = T c /ET o ; Allen et al. 1998;Pereira et al. 2024). These coefficients are an operative tool for farmers and technicians when irrigation scheduling is performed based on the daily crop water demand using the two step approach (Allen et al. 1998). It is worth noting those crop coefficients should be computed for an almond crop under pristine conditions (Pereira et al. 2015). ...
... As discussed above, K c and K cb values over the crop growing season are strongly related to a variety of vegetation parameters, including f c , h, LAI or the fraction of the intercepted photosynthetic active radiation (f IPAR ) which is assumed as an estimate of f c (Pereira et al. 2020b). Allen et al. (1998) introduced a standardized approach to relate K cb during the midseason period, K cb mid , to LAI or f c using a K cb value representing K cb under conditions of full cover. Allen and Pereira (2009) later developed a method for predicting actual crops coefficients from f c and h, (hereinafter the A&P approach), who showed that this approach performs particularly well for fruit trees and vines. ...
The aim of this study was to estimate standard crop coefficients of surface and sub-surface drip-irrigated young almond trees under non-limiting soil water content conditions, based on measurements of the fraction of ground covered by the canopy (fc) and tree height (h) (A&P approach proposed by Allen and Pereira (2009)) and to improve the transferability of them to the productive sector once weather data (i.e. maximum and minimum air temperature (Tmax and Tmin, respectively), as well as dew point temperature (Tdew)) were adjusted to the reference conditions. A 4 year field experiment was carried out in a ~ 12.5 ha commercial young almond (Prunus dulcis (Mill.) D.A. Webb) orchard located in Hellín, (SE Spain). ‘Penta’ almond trees, grafted onto the GF-677 rootstock, were planted in 2018. Field measurements of fc and h were performed over four consecutive growing seasons from 2019 to 2022. In parallel, ETo computed by the nearest meteorological station, located at a non-reference weather site, was reduced around 6% after bringing weather data closer to the reference conditions, while actual crop evapotranspiration and its components (actual tree transpiration and soil evaporation) were estimated in each irrigation system through the so-called simplified two-source energy balance (STSEB) model in order to be used as a quality assessment of the A&P approach. The ratio between the former estimations and the ETo allowed to compute STSEB-based crop coefficients. No significant differences in effective canopy cover (fc eff) nor h were observed between the two irrigation systems, and thus the estimated Kcb values were the same for both drip-irrigation systems. fc eff values during mid-season stage ranged between 0.15 in 2019 and 0.62 in 2022, whereas average h values for this stage ranged between 2.36 and 3.80 m in 2019 and 2022, respectively. These values of fc eff and h resulted in average mid-season basal crop coefficients (Kcb-mid) of 0.28 in 2019, 0.39 in 2020, 0.61 in 2021 and 1.02 in 2022. Soil evaporation estimates through STSEB model were significantly different between the two irrigation systems, leading to differences in Ke being around 16% higher for DI than SDI. Moreover, the intra-annual Kc values moved in the same range for the initial, mid- and end-season crop growth stages, varying from 0.30 in 2019 to 1.01 in 2022, computed under standard conditions. Finally, the A&P approach was shown to be an especially interesting method for estimating Kcb values in almond fruit trees, being useful for refining Kcb and/or Kc for conditions of plant spacing, size and density that may differ from standard values. In this way, irrigation scheduling can be optimized regarding the almond tree architecture (i.e. fc eff and h), allowing to manage properly irrigation water to meet the tree water demands.
... where Kcb is the basal crop coefficient, Ks is the water stress coefficient, and Ke is the soil evaporation coefficient. Basal crop coefficients were estimated using techniques explained in Allen et. al. (1998) [63] and elaborated in Allen et. al. (2005) [64], with modifications Figure 1. Study locations with site numbers, data sources, and regional groupings used in this study. ...
... where K cb is the basal crop coefficient, K s is the water stress coefficient, and K e is the soil evaporation coefficient. Basal crop coefficients were estimated using techniques explained in Allen et al. (1998) [63] and elaborated in Allen et al. (2005) [64], with modifications noted in Annex 1 of Allen et al. (2007) [65]. The K cb was modified with the water stress coefficient K s because the actual ET is often lower because irrigation practices in arid western environs are often unable to maintain the ideal soil water content. ...
... where K cb is the basal crop coefficient, K s is the water stress coefficient, and K e is the soil evaporation coefficient. Basal crop coefficients were estimated using techniques explained in Allen et al. (1998) [63] and elaborated in Allen et al. (2005) [64], with modifications noted in Annex 1 of Allen et al. (2007) [65]. The K cb was modified with the water stress coefficient K s because the actual ET is often lower because irrigation practices in arid western environs are often unable to maintain the ideal soil water content. ...
Communities throughout the United States have come to rely upon agriculture as a pillar of their political integrity, economic security, and health and wellbeing. Climatic conditions in the western portion of the United States necessitate most lands be irrigated to be arable. As a result, a major portion of the economy of the United States, and by extension the world economy, is driven by the continued viability of western United States water law and policy. Furthermore, due to the strong interrelationship between anthropogenic consumptive uses, streamflows, and wetland/riparian area ecology, irrigation demand has a strong effect on stream morphology, quality, and biology for aquatic species. Western water management is a complex mosaic that is controlled by western state, federal, and tribal governments. Each of these systems of law have vulnerabilities to climate change, which is well understood to cause increasing water supply scarcity. This articledemonstrates the risks climate change poses to our management of irrigation water demand, as well as the interrelationship between water supply and demand. Due to the shared nature of the resource, this article addresses both tribal reserved rights and state-based rights using data from Indian reservations that either contain and/or are closely adjacent to non-tribal agricultural communities. Those data are used in a systems–dynamics model to integrate crop–water requirement estimation techniques with climate change estimates and a Monte Carlo analysis to assess how irrigation demand could change because of changing temperature, precipitation, incoming radiation, and wind speed caused by climate change. Results indicate that climate change will cause increases in irrigation requirements at most locations. Further, climate change is expected to significantly increase seasonal variability in many locations. The model provides a useful tool based upon publicly available data that will allow individual water users to make conservation decisions necessary to preserve their water rights as the climate changes.
... These adjustments consider factors such as the crop's height, the wind's speed and the minimum relative humidity, which influence both crop and aerodynamic resistance. Initial values of Kc should be mainly determined by soil type and the status of irrigation (23). Identifying crop phenology at each site and aligning tabulated Kc values with actual growth periods is crucial (24). ...
... Using the locally developed Kc value, the seasonal ETa for maize ranged from 342.6 mm to 372 mm, averaging 355.6 mm ( Table 1). These findings underscore the utility of the dual Kc method for accurately estimating ETa, which aids in irrigation scheduling and total water use calculations, particularly considering the frequency of wetting (23). better water management and irrigation scheduling, optimizing CWUE under varying soil and climate conditions. ...
Accurately estimating crop water use is crucial for efficient water management in conservation agriculture, especially in Coimbatore's semiarid climate. This study assessed maize water use and productivity over three growing seasons (2023-2024) at AC&RI, Coimbatore. Irrigation applied each season varied between 500.8mm and 554.1 mm, averaging 535.8 mm, while total water supply ranged from 810.6 to 985.3 mm. Actual evapotranspiration (ETa) was estimated using locally developed crop coefficient curves (Lkc) and FAO crop coefficients. Water productivity for maize was calculated based on these estimates. Daily ETa for maize ranged from 0.9mm to 8.2 mm. Other than the different seasons, ETa varied from 342.6 to 372 mm, averaging 355.6 mm with the Lkc curve. By FAO Kc, ETa ranged from 400.8mm to 479.1 mm, with an average of 444.2 mm. The irrigation requirement ranged from 579.6mm to 672.7 mm, with an average of 629.5 mm using LKc. Using FAO Kc, the range was 637.8mm to 762.9 mm, with an average of 718 mm. Crop water use efficiency (CWUE) ranged from 0.8 and 0.9 kg/m³, with an average of 0.9 kg/m³. The evapotranspiration water use efficiency (ETWUE) ranged from 2.0 to 2.1 kg/m³, with an average of 2.1 kg/m³. The irrigation water use efficiency (IWUE) varied across seasons, averaging 1.4 kg/m³. Strong correlations were observed between CWUE, IWUE, and the amount of seasonal irrigation (R² = 0.98 and 0.99, respectively). CWUE and ETWUE strongly correlated with IWUE (R² = 0.98 and 0.75, respectively). These findings suggest that maize irrigation in Coimbatore's semiarid regions should be tailored to local conditions to enhance water productivity.
... Readers are encouraged to review previous year analysis reports Pearson et al., 2019;Pearson et al., 2020) for specifics on ET Demands model set-up and development for the UCRB ET feasibility study. Detailed descriptions of the ET Demands model and approach is included in Allen et al. (2005), Allen and Robison (2009), and Huntington et al. (2015). Specifics related to the Python ET Demands software and application can be found at: https://github.com/usbr/et-demands ...
... In this study, the ratio of annual effective precipitation to annual precipitation (PPT) was estimated and summarized as the crop area weighted average for each ET Cell and highlighted as an annual time series for grass hay (highlighted in Results Section). For more information on details of the ET Demands model and algorithm specifics see Allen et al. (2005), Robinson (2009), andHuntington et al. (2015). ...
This report summarizes application of the ET Demands model v1.1.0 to the Upper
Colorado River Basin (UCRB) for the 2020 calendar year (Figure 1). The 2020 analysis builds upon previous model runs performed for 2017, 2018, and 2019. Model set-up and description sections contain recycled text from previous year reports for consistency. The ET Demands model was applied to develop daily, monthly, seasonal, and annual crop evapotranspiration (ETc) and Net Irrigation Water Requirement (NIWR) estimates for irrigated croplands within the UCRB. ET Demands modeling was performed in collaboration with the Bureau of Reclamation
and Wilson Water Group as part of a multiyear feasibility study to operationally estimate ET within the UCRB.
... The Dual-K c is the approach used by WEAP model, which is considered more complicated than the simple approach, where the crop coefficient (K c ) is divided into the "Basal" crop coefficient (K cb ) and the (K e ) coefficient that represents the evaporation from the soil [12] as in Figure 3. The total crop Evapotranspiration (ET c ) is calculated as the result of multiplying the reference Evapotranspiration (ET 0 ) by the sum of two coefficients (K cb +K e ) according to the following equation [13]: ...
... Total cultivated area of project by second scenario after Improving The water used for Ramadi irrigation project represent 34.2% from Ramadi irrigation budget from Euphrates River. 2-Despite of, the total water requirement increased by 144% from 111.5 3 /year to 272.12 3 /year, the economic returns increased by 307% from 16.04 million $ /year to 65.24 million $. 3-When using additional pumps for project 2 and project 3 by 1 3 /s and 2 3 /s for project 5, respectively, the economics return increased by 441% from 16.04 million $ /year to 86.79 million $ / year. 4-The convey loss increased from 16.72 million 3 /year to 48.47 million 3 /year, when applied second scenario. ...
... The Penman-Monteith equation, a recommended approach for incorporating climate factors, rectifies inconsistencies in trends when meteorological elements are excluded [45,46]. Further, according to Mashabatu et al. [34], the FAO-56 coefficient approach by Allen et al. [47] was the most used method across the retrieved studies. Therefore, the current study employed the CROPWAT model to calculate reference evapotranspiration (ETo) using the FAO's Penman-Monteith equation and meteorological data. ...
... As in our case study, the Penman-Monteith method is advised for calculating crop water demands, particularly for planning purposes [69]. The CROPWAT 8.0 model calculates the ETo using the FAO's Penman-Monteith equation and recorded meteorological data, as shown in Equation (6) [47]. ...
Expanding projects to reclaim marginal land is the most effective way to reduce land use pressures in densely populated areas, such as Egypt’s Nile Valley and Delta; however, this requires careful, sustainable land use planning. This study assessed the agricultural potential of the El-Dabaa area in the northern region of the Western Desert, Egypt. It focused on assessing land capability, evaluating crop suitability, mapping soil variability, and calculating crop water requirements for twenty different crops. In this work, we evaluated land capability using the modified Storie index model and assessed soil suitability using the land use suitability evaluation tool (LUSET). We also calculated crop water requirements (CWRs) utilizing the FAO-CROPWAT 8.0 model. Additionally, we employed ArcGIS 10.8 to create spatial variability maps of soil properties, land capability classes, and suitability classes. Using a systematic sampling grid, 100 soil profiles were excavated to represent the spatial variability of the soil in the study area, and the physicochemical parameters of the soil samples were analyzed. The results indicated that the study area is primarily characterized by flat to gently sloping surfaces with deep soils. Furthermore, there are no restrictions on soil salinity or alkalinity, no sodicity hazards, and low CaCO3 levels. On the other hand, the soils in the study area are coarse textured and have low levels of CEC and organic matter (OM), which are the major soil limiting factors. As a result, the land with fair capability (Grade 3) accounted for the vast majority of the study area (87.3%), covering 30599.4 ha. Land with poor capability (Grade 4) accounted for 6.5% of the total area, while non-agricultural land (Grade 5) accounted for less than 1%. These findings revealed that S2 and S3 are the dominant soil suitability classes for all the studied crops, indicating moderate and marginal soil suitabilities. Furthermore, there were only a few soil proportions classified as unsuitable (N class) for fruit crops, maize, and groundnuts. Among the crops studied, barley, wheat, sorghum, alfalfa, olives, citrus, potatoes, onions, tomatoes, sunflowers, safflowers, and soybeans are the most suitable for cultivation in the study area. The reference evapotranspiration (ETo) varied between 2.6 and 5.9 mm day⁻¹, with higher rates observed in the summer months and lower rates in the winter months. Therefore, the increase in summer ETo rates and the decrease in winter ones result in higher CWRs during the summer season and lower ones during the winter season. The CWRs for the crops we studied ranged from 183.9 to 1644.8 mm season⁻¹. These research findings suggest that the study area is suitable for cultivating a variety of crops. Crop production in the study area can be improved by adding organic matter to the soil, choosing drought-resistant crop varieties, employing effective irrigation systems, and implementing proper management practices. This study also provides valuable information for land managers to identify physical constraints and management needs for sustainable crop production. Furthermore, it offers valuable insights to aid investors, farmers, and governments in making informed decisions for agricultural development in the study region and similar arid and semiarid regions worldwide.
... [32][33][34], the Bowen ratio energy balance method, soil water balance or a lysimeter as reviewed by [35]. The partitioning of evapotranspiration may be performed combining soil evaporation measured in micro-lysimeters or mini-lysimeters [36] with actual crop transpiration estimations with sap flow methods [37][38][39]. In addition, models properly calibrated allows assessing crop water requirements, to auxiliar adequately in the management of irrigation, and analysing the impact of crops and management, including under water deficit conditions. ...
... The value of Kr depends on the cumulative depth of water depleted from the topsoil and is daily calculated through the soil water balance considering the soil evaporation layer's thickness (Ze, m). Calculations are based on the assumption that the drying cycle happens in two stages, with the water 8 in the topsoil and the energy available at the soilʹs surface limiting the first stage [36,48], thus with Kr reducing once the evaporated depleted water exceeds the readily evaporable water (REW). Thus, Kr is computed as: ...
Soil water balance (SWB) in woody crops is sometimes difficult to estimate with one-dimensional models because these crops do not completely cover the soil and usually have a deep root system, particularly when cropped under rainfed conditions in a Mediterranean climate. In this study, the actual crop evapotranspiration (ETc act) is estimated with the soil water balance model SIMDualKc which uses the dual-Kc approach (relating the fraction of soil cover with the crop coefficients) to improve the estimation of the water requirements of a rainfed vineyard, using data from a deep soil profile. The actual basal crop coefficient (Kcb act) obtained using the SIMDualKc model was compared with the Kcb act estimated using the A&P approach, which is a simplified approach based on measurements of the fraction of ground cover and crop height. Spectral vegetation indices derived from Landsat-5 satellite data were used to determine the fraction of ground cover (fc VI) and thus, the density coefficient (Kd). The SIMDualKc model was calibrated using soil water content (SWC) measurements down to a depth of 1.85 meters, which significantly improved the conditions for using a SWB estimation model. The test of the model was performed using a different SWC dataset. A good agreement between simulated and field measured SWC was observed for both data sets along the crop season, with RMSE<12.0 mm, NRMSE <13%. The calibrated Kcb values were 0.15, 0.60 and 0.52 for the initial, mid-season, and end season, respectively. The ratio between actual (ETc act) and crop evapotranspiration (ETc) was quite low between veraison and maturity (mid-season), corresponding to 36%, indicating that the rainfall was not sufficient to satisfy the vineyards water requirements. Spectral vegetation indices used to compute fc VI were unable to fully track the plants’ conditions when water stress. However, ingestion of data from remote sensing showed promising results that could be used to support decisions making in irrigation scheduling. Further studies on the use of the A&P approach using remote sensing data are required.
... El riego de la parcela se manejó para mantener un elevado contenido de agua en el suelo que evitase cualquier estrés hídrico; para ello, se llevó a cabo una programación diaria del riego basada en el balance de agua del suelo según el método FAO56. La evapotranspiración del cultivo (ETc) se calculó multiplicando la evapotranspiración de referencia (ETo) por un coeficiente de cultivo dual, compuesto por un coeficiente de cultivo basal (Kcb) que representa la transpiración del cultivo (Tc = Kcb×ETo) y un coeficiente de evaporación (Ke), que representa la evaporación del suelo (Es = Ke×ETo) (Allen et al., 1998(Allen et al., , 2005 Kcb full para su uso con la ETo se puede estimar de la siguiente manera: ...
En los últimos años se está produciendo un crecimiento significativo de la superficie cultivada de almendros en zonas áridas y semiáridas de la cuenca Mediterránea con escasez de recursos hídricos. Este crecimiento está siendo exponencial en algunas zonas de España, como es el caso de Castilla‐La Mancha. Las principales razones han sido la mecanización de la recolección, un considerable incremento de la demanda global, que ha llevado a un aumento gradual del precio pagado al agricultor, y la introducción de nuevas variedades de floración tardía y extra‐tardía que reducen el riesgo de pérdidas de producción por heladas primaverales. Muchas de estas nuevas plantaciones se cultivan en condiciones de regadío, por lo que la determinación precisa de los coeficientes de cultivo es necesario para optimizar la programación del riego e incrementar la eficiencia en el uso del agua de este cultivo. El objetivo de este estudio fue estimar los valores del coeficiente de cultivo basal, Kcb, (componente transpirativa) para una plantación joven de almendros regados por goteo al 100% de sus necesidades hídricas y sin ningún otro tipo de estrés. Para ello, se utilizó la metodología propuesta por Allen&Pereira (2009), basada en medidas de la fracción de suelo cubierta por vegetación (fc) y la altura del cultivo (h). El experimento se llevó a cabo durante tres campañas consecutivas (2019‐2021) en una parcela comercial de 12,5 ha de almendros (Prunus dulcis (Mill.) D.A. Webb) localizada en Hellín (Albacete). Los árboles de la variedad ‘Penta’ se injertaron sobre el patrón GF‐677 en 2018. El marco de plantación fue de 6 m entre filas de árboles y 5 m entre plantas de la misma fila, dando lugar a 333 árboles ha‐1. Las medidas de fc y h se llevaron a cabo cada 15 días a lo largo de las tres campañas experimentales. Los valores directamente medidos de fc se convirtieron a valores de fracción de cobertura efectivos (fc eff) a partir del ángulo de inclinación del sol (β) cerca del mediodía solar. Los valores medios de fc eff durante la fase de mitad de temporada variaron entre 0,16 en 2019 y 0,38 en 2021, mientras que la altura media en esta fase osciló entre 2,36 m en 2019 y 3,45 m en 2021. Estos valores de fc eff y h dieron lugar a unos valores medios del coeficiente de cultivo basal en la fase de mediados de temporada (Kcb mid) de 0,30 en 2019, 0,45 en 2020 y 0,55 en 2021. Los valores de Kcb mid fueron ajustados a las condiciones climáticas templadas estándar (humedad relativa mínima del 45% y velocidad del viento de 2 m s‐1), lo que permite transferirlos a otras zonas con condiciones climáticas diferentes.
... Additionally, yearly climatic data were also collected from the Ethiopian National Meteorological Service Agency. Crop data (development stages, crop coefficient, rooting depth, critical depletion level, and yield response factor) were also collected from secondary data (Allen et al., 2016;Luo et al., 2022). ...
Evaluating the performance of irrigation schemes is crucial to identify key problems that impede scheme efficiencies and the utilization of available resources. Accordingly, the objective of this study was to evaluate the performance of Dabasso Lamaffa small-scale irrigation scheme. The study was carried out during the cropping season from November up to March 2015 E.C. Primary and secondary data were collected for implementing the efficiency and productivity of the scheme. To collect and measure the relevant data at the field level, the three representative farmers’ fields were selected at the head, middle, and tail-end water users in the irrigation scheme. Both internal and external performance indicators were considered for evaluation of the scheme. The internal indicators were conveyance efficiency, application efficiency, storage efficiency, distribution uniformity, and deep percolation ratio. The external indicators were agricultural output, water supply indicators, water delivery capacity indicators, physical indicators, and economic and financial indicators. The result reveals that the average efficiency of conveyance, application, storage, deep percolation ratio, and the distribution uniformity of the scheme were 76.44%, 30.47%, 82.74%, 69.53%, and 95.29%, respectively. The overall efficiency of the scheme was 23.29%, showing that the performance was poor, and it was caused mainly due to the water application problem at the field. The agricultural output productivity was 2620.83 (US/ha), 0.94 (US/m ³ ), respectively, for output per unit irrigated area, output per unit command area, output per unit irrigation diverted, and output per unit water consumed. This result reveals that it was in a recommended output production, and in these regards the scheme was productive. The water supply indicators, such as relative irrigation supply (RIS) and relative water supply (RWS), were 2.13 and 2.05, which shows that there was no deficiency of water and it was supplied in excess. However, the water delivery capacity of the scheme was low, which was 83%, and it needs improvement. The irrigation ratio and the sustainability of the irrigation scheme were also good, showing there will be a continuation of using the scheme in the future. Awareness creation for the farmers on the field water management is essential to improve the economic and financial benefit of the scheme in the future.
... Remote sensing ET models have been a significant area of research (Su, 2002;Courault et al., 2005;Li et al., 2009;Liou and Kar, 2014;Merlin et al., 2014;Yao et al., 2014;Zhang et al., 2016;Tran et al., 2023). ET models are based on the crop coefficient (Allen et al., 1998(Allen et al., , 2011a(Allen et al., , 2005, or on energy balance approaches. The latter includes initial empirical models that rely on the difference between surface and air temperature (Carlson and Buffum, 1989;Jackson et al., 1977;Nieuwenhuis et al., 1985;Seguin et al., 1994), as well as the more recent and complex surface energy balance models (McShane et al., 2017). ...
Accurate and synoptic estimation of Evapotranspiration (ET) is crucial for water management. A Google Earth Engine workflow is implemented to estimate daily ET at 30m. The algorithm uses Landsat and ERA5-Land datasets and includes the Two Source Energy Balance (TSEB) model, an Artificial Neural Network for Leaf Area Index, and a gap-filling approach based on crop coefficient. The outputs were evaluated against four local flux towers in a semi-arid site in Morocco (wheat, maize, watermelon, olive), and compared to another high-resolution ET (SSEBop product). The results demonstrated good performances (RMSE between 0.67mm/day and 2mm/day, low MBE), while SSEBop product generally underestimated ET. Better performance of the TSEB-GEE workflow was found when aggregating ET to weekly and monthly timescales. The workflow offers ease of model implementation to deliver reliable daily plot-scale ET estimates, offering the potential for broader-scale applications in semi-arid Mediterranean regions, encompassing various crops and facilitating historical analysis.
... of the irrigation structure were collected through direct measurement, laboratory and fieldwork, field observation, stakeholder interviews, and questionnaires. Secondary data such as meteorological data, crop property data which are input for the CROPWAT software such as root length of the crop, depletion of the crop, crop coefficient, and crop patterns (Allen et al., 2016;Luo et al., 2022), were collected from National Meteorological Service Agency (NMSA) and relevant documents, studies, and other useful written materials. The command area and maintenance cost were collected from the design documents and interviewing the Agricultural Office experts. ...
A study was carried out from November to May in the cropping season of 2016E.C to evaluate the performance of Temsa small scale irrigation scheme. Both internal and external indicators were considered for evaluation. The internal indicator efficiencies such as conveyance, application, storage, distribution uniformity, and deep percolation ratio and the external indicators such as agricultural output, water supply, water delivery capacity, physical, and economic and financial indicators were evaluated. The result reveals that, the average conveyance efficiency of the main, secondary, and tertiary canals were 79.6%, 85.6%, and 84.7%, respectively. The scheme has on average application efficiency (Ea), storage efficiency, deep percolation ratio, and distribution uniformity of 40.87%, 78.04%, 59.70%, and 93.33%, respectively. The poor Ea and low conveyance efficiency of the canal affected the overall scheme performance. The result reveals that, the overall efficiency of the scheme was 23.19%. The four basic agricultural output indicators of the scheme such as output per unit irrigated area, output per unit command area, output per unit irrigation diverted, and output per unit water consumed were 4,738.58 US/ha, 1.16 US/m³, respectively. This shows that, the command area was beneficial and was giving a revenue for the farmers at the cropping season. The relative irrigation supply and the water delivery capacity of the canal were 2.37 m³ and 83%, respectively. In the current study, the irrigation ratio and the sustainability of the irrigated area were 0.25 and 0.43, respectively. The irrigation ratio was low due to the designing problem. Availability of water throughout the year and market accessibility near the scheme were the advantage of the scheme that encourage the farmers. However, the input costs were affecting the return obtained from the product. Hence it is better to provide access to credit for the sustainable production and improve the farmers income.
... Liu et al. [23] applied the SIMDualKc model [38] to compute the soil water balance and assess the impact of soil salinity on actual crop evapotranspiration rates. The SIMDualKc model used the dual crop coefficient approach [21,39,40] to estimate crop evapotranspiration (ET c ) by separately computing its components crop transpiration (T c ) and soil evaporation (E s ). In this approach, a basal crop coefficient (K cb ), which describes the transpiration characteristics that distinguish a specific crop from the reference grass crop, is used to calculate T c (T c = K cb ET o ). ...
The need for controlling salinity in arid zones is essential for sustainable agricultural production and irrigation water use. A case study performed for two years in Hetao, Inner Mongolia, China, is used herein to rethink the contradictory issues of arid lands represented by water saving and controlling soil and water salinity. Two sets of static lysimeters, where water table depths (WTDs) were fixed at 1.25, 150, 2.00, and 2.25 m, were continuously monitored, and soil water and solute data were used to calibrate and validate two models: the soil water balance model SIMDualKc and the deterministic soil water and salt dynamics model HYDRUS-1D. Once accurately calibrated, the models were used to simulate maize water use, percolation, and capillary rise, along with the observed variables for the actual WTD and the autumn irrigation applied. Simulation scenarios also considered agricultural system degradation and dynamic water table behavior. Results have shown that large leaching efficiencies (Lefs) were obtained for large irrigation depths in cases of shallow water tables, but higher Lefs corresponded to high application depths when the water table was deeper. Agricultural system degradation, particularly increased groundwater salinity, lowered Lef, regardless of WTD. Conversely, water savings were minimal and only achievable when considering the dynamic nature of groundwater. These results indicate that there is a need to define different WTDs based on soil characteristics that influence fluxes and root zone storage, as well as the impacts of newly installed drainage systems aimed at salt extraction.
... A daily irrigation schedule was computed according to the FAO56 dual crop coefficient methodology, where a simplified water balance for the root zone of the crop was used to compute the soil water depletion (Dr,I; Allen et al., 1998Allen et al., , 2005. For computing a soil water balance (SWB), the inputs (effective precipitation, Pe, and irrigation depth, I) and outputs (crop evapotranspiration, ETc, deep percolation, DP, and Dr,i-1) in the root zone were taken into account. ...
... In parallel, and regarding large irrigation areas, the methodology follows the dual crop coefficient approach (Wright, 1982) as it allows for ET cadj-RSb estimations (equation (7)) when crops do not fully cover the ground, like woody crops, most of the vegetable ones or herbaceous crops in their first development stages (Allen et al., 2005). Taking into account the great crop diversity and different local irrigation management practices involved in large river basin areas, the use of tabulated values for the K cb or f c is avoided, as recommended by the FAO56 approach, because it needs to be locally adapted (Allen et al., 1998). ...
Since the development of Water Footprint environmental indicator, significant research on blue and green crop water use and the respective water footprint estimations has been published. Such research is commonly approached using different methodologies that leverage tabulated values for crop development characterisation, while studies based on remote sensing data are less abundant, despite crop monitoring using remote sensing-based vegetation indices having demonstrated great capabilities and operability. To help fill this gap, we present a methodology that uses a remote sensing vegetation index time series from Sentinel-2 satellite near infra-red and red spectral bands data to derive basal crop coefficient time series to subsequently be used under the Remote Sensing-based Soil Water Balance approach that follows the globally operative FAO56 procedure. It provides pixel-based temporal and spatially distributed estimations of net irrigation requirements and adjusted crop evapotranspiration, with the aim being to divide up the latter and estimate the remote sensing-based green and blue crop water use and the subsequent green and blue water footprint. This is all done under the Agricultural Water Footprint Assessment framework for a growing crop or tree. This methodology was applied over a large, crop-diverse Spanish river basin district (Júcar) and across two different climatological years (humid vs. dry). Its feasibility was demonstrated by the acceptable behaviour of the remote sensing-based blue crop water use estimation for different herbaceous and woody crops, against the official dataset for irrigation water accounting at two water management scales (of a relative mean absolute error of 15.4 % in the case of the largest water user association and of 17.1 % in the case of the river basin water authorities’ own estimations). The proposed approach, which we call Remote Sensing-based Agricultural Water Accounting and Footprint, aims to provide reliable and accurate spatially and temporally distributed thematic cartography about the remote sensing-based blue and green crop water use and water footprint. This information is essential for water managers with the goal of generating transparent and complementary information to incorporate into their own working scales.
... The ETcadj p,t estimates are obtained using the dual crop coefficient approach [49], which is suitable for crops that do not fully cover the ground like woody crops, most of the vegetables or the herbaceous crops at its first development stages [50]. ...
... The value of K r depends on the cumulative depth of water depleted from the topsoil and is calculated daily through the soil water balance considering the soil evaporation layer's thickness (Z e , m). Calculations are based on the assumption that the drying cycle happens in two stages, with the water in the topsoil and the energy available at the soil's surface limiting the first stage [36,48] and thus with K r reducing once the evaporated depleted water exceeds the readily evaporable water (REW). Thus, K r is computed as follows: ...
Soil water balance (SWB) in woody crops is sometimes difficult to estimate with one-dimensional models because these crops do not completely cover the soil and usually have a deep root system, particularly when cropped under rainfed conditions in a Mediterranean climate. In this study, the actual crop evapotranspiration (ETc act) is estimated with the soil water balance model SIMDualKc which uses the dual-Kc approach (relating the fraction of soil cover with the crop coefficients) to improve the estimation of the water requirements of a rainfed vineyard, using data from a deep soil profile. The actual basal crop coefficient (Kcb act) obtained using the SIMDualKc model was compared with the Kcb act estimated using the A&P approach, which is a simplified approach based on measurements of the fraction of ground cover and crop height. Spectral vegetation indices (VIs) derived from Landsat-5 satellite data were used to determine the fraction of ground cover (fc VI) and thus the density coefficient (Kd). The SIMDualKc model was calibrated using available soil water (ASW) measurements down to a depth of 1.85 m, which significantly improved the conditions for using an SWB estimation model. The test of the model was performed using a different ASW dataset. A good agreement between simulated and field-measured ASW was observed for both data sets along the crop season, with RMSE < 12.0 mm and NRMSE < 13%. The calibrated Kcb values were 0.15, 0.60, and 0.52 for the initial, mid-season, and end season, respectively. The ratio between ETc act and crop evapotranspiration (ETc) was quite low between veraison and maturity (mid-season), corresponding to 36%, indicating that the rainfall was not sufficient to satisfy the vineyard’s water requirements. VIs used to compute fc VI were unable to fully track the plants’ conditions during water stress. However, ingestion of data from remote sensing (RS) showed promising results that could be used to support decision making in irrigation scheduling. Further studies on the use of the A&P approach using RS data are required.
... ET by these models is derived from the integration of radiometric land surface temperature (LST), and biophysical variables, i.e., leaf area index (LAI), photosynthetically active radiation (PAR), fractional vegetation cover (FVC), clumping index, leaf angles, canopy height, leaf abundance, ecosystem hierarchy, etc. [8,9]. Some other techniques are based on net radiation and temperature differentials [10,11], or an inferential approach constrained by crop coefficients [12][13][14]. These simple generic models do not account for the horizontal movement of soil energy fluxes and water and heat storage [15][16][17][18]. ...
Accurate evapotranspiration (ET) estimation is crucial for sustainable water management in the diverse and water-scarce Mediterranean region. This study compares three prominent models (Simulator of Terrestrial Ecohydrological Processes and Systems (STEPS), Soil-Canopy-Observation of Photosynthesis and Energy fluxes (SCOPE), and Two-Source Energy Balance (TSEB)) with established global datasets (Moderate Resolution Imaging Spectroradiometer 8-day global terrestrial product (MOD16A2), Global Land Evaporation Amsterdam Model (GLEAM), and TerraClimate) at multiple spatial and temporal scales and validates model outcomes with eddy covariance based ground measurements. Insufficient ground-based observations limit comprehensive model validation in the eastern Mediterranean part (Turkey and Balkans). The results reveal significant discrepancies among models and datasets, highlighting the challenges of capturing ET variability in this complex region. Differences are attributed to variations in ecosystem type, energy balance calculations, and water availability constraints. Ground validation shows that STEPS performs well in some French and Italian forests and crops sites but struggles with seasonal ET patterns in some locations. SCOPE mostly overestimates ET due to detailed radiation flux calculations and lacks accurate water limitation representation. TSEB faces challenges in capturing ET variations across different ecosystems at a coarser 10 km resolution. No single model and global dataset accurately represent ET across the entire region. Model performance varies by region and ecosystem. As GLEAM and TSEB excel in semi-arid Savannahs, STEPS and SCOPE are better in grasslands, croplands, and forests in few locations (5 out of 18 sites) which indicates these models need calibration for other locations and ecosystem types. Thus, a region-specific model calibration and validation, sensitive to extremely humid and arid conditions can improve ET estimation across the diverse Mediterranean region.
... However, the available energy for surface evaporation constrains the combined crop coefficient to K cb + K e ≤ K c max . As the soil surface dries, soil evaporation becomes directly proportional to the remaining soil moisture content [49]. K e = min(k r (k c max − K cb ), f ew K cmax ) ...
The impact of the intercropping system on the soil–plant–atmosphere continuum (SPAC), encompassing soil evaporation, soil moisture dynamics, and crop transpiration, remains an area of uncertainty. Field experiments were conducted for two years in conjunction with the SIMDualKc (Simulation Dual Crop Coefficient) model to simulate two planting configurations: sole-cropped wolfberry (Lycium barbarum L.) (D) and wolfberry intercropped with alfalfa (Medicago sativa L.) (J). These configurations were subjected to different irrigation levels: full irrigation (W1, 75–85% θfc), mild deficit irrigation (W2, 65–75% θfc), moderate deficit irrigation (W3, 55–65% θfc), and severe deficit irrigation (W4, 45–55% θfc). The findings revealed that the JW1 treatment reduced the annual average soil evaporation by 32% compared with that of DW1. Additionally, mild, moderate, and severe deficit irrigation reduced soil evaporation by 17, 24, and 36%, respectively, compared with full irrigation. The intercropping system exhibited a more efficient canopy structure, resulting in reduced soil evaporation and alleviation of water stress to a certain extent. In terms of temporal dynamics, monocropping resulted in soil moisture levels from 1% to 15% higher than intercropping, with the most significant differences manifesting in the mid to late stages, whereas differences in the early stages were not statistically significant. Spatially, the intercropping system exhibited 7–19% lower soil water contents (SWCs) than sole cropping, primarily within the root water uptake zone within the 0–60 cm soil layer. The intercropping system showed an enhanced water absorption capacity for plant transpiration, resulting in a 29% increase in transpiration compared with sole cropping, thereby achieving water-saving benefits. These findings contribute to our understanding of the agronomic and environmental implications of intercropping wolfberry and alfalfa in arid regions and provide insights into optimizing water and soil resource management for sustainable agricultural practices.
... Las nuevas plantaciones de olivar en seto monovarietales, además de reducir la biodiversidad, presentan elevados insumos entre los que se encuentra el suministro de agua, por lo que es de especial interés el uso eficiente de agua de riego para reducir los impactos ecológicos (Guerrero-Casado et al., 2021). El método más utilizado para la programación del riego en olivares es el que se basa en el cálculo de la evapotranspiración del cultivo (ETc), tanto por el método propuesto por FAO (Allen et al., 1998) como por otros posteriores también basados en multiplicar la evapotranspiración de referencia por uno o varios coeficientes (Allen et al., 2005;Paço et al., 2019). En la mayoría de los trabajos realizados sobre RD se utiliza como referencia esta ETc a la que se aplica un porcentaje de reducción, bien para todo el ciclo para un riego deficitario sostenido Ramos y Santos, 2010), con coeficientes diferentes en función del estado fenológico del cultivo si se trata de un riego deficitario controlado Padilla-Díaz et al., 2016), o dotaciones fijas condicionadas a la disponibilidad de recursos hídricos (Martínez-Gimeno et al., 2022). ...
The 1990s saw the emergence of a system of olive cultivation known as super intensive or hedgerow, based on high planting densities. The total mechanization of
cultivation and the speed with which it was introduced led to its rapid spread in many
olive growing countries and even in countries without a tradition of this crop. Despite
this success, it presents several problems, such as the excessive vigor of the current
varieties, which requires good management to be sustainable.
In this work we present the results of eleven years (2009 2019) in a hedgerow
olive plantation of the 'Arbequina' variety, located in Vegas del Guadiana (Badajoz,
Spain) and planted in 2008. Four irrigation treatments were established: Control,
irrigated to cover the water needs of the olive trees and three controlled deficit
treatments (RDC) with different levels of water stress, RDC 1 (mild), RDC 2 (moderate)
and RDC 3 (severe). Deficit treatments were established according to stem water
potential levels, differentiating between growth stages: in stage I (flowering to pit
hardening) the lower limits were 1.0, 1.4 and 2.0 MPa for RDC 1, 2 and 3 respectively;
in stage II (pit hardening to veraison) 1.4, 2.0 and 3.0 MPa; while in stage III (veraison
to harvest) they were 1.2, 1.6 and 1.6 MPa.
The main objective of this work is to provide information to support the sustainability of super intensive olive growing systems by evaluating the short-medium and long-term response to the application of these vigor control strategies, also looking for a balance between production and olive oil quality. A remarkable aspect of this work is that the treatments have been maintained with the same criteria from the second year of planting throughout the following eleven years, in such a way that they can be analysed at each stage of development, as well as the cumulative effect.
Three stages are distinguished: hedgerow formation from 2009 2011 ( juvenile ), full
production between 2012 2015 (adult 1) and signs of declining or stabilizing production
in the years 2016 2019 (adult 2).
Chapter 3 deals with the control of vigor in hedgerow olive groves with the variety most used in this system (Arbequina). Firstly, the effect of the strategies applied on the water status of the olive trees and on the vegetative development is analyzed by quantifying different aspects. The results show that the application of moderate and severe strategies delayed the formation of hedges, but maintained a lower, more rejuvenated, and less supported canopy in the following years. The light deficit treatment achieved a similar level of growth to the most irrigated in the early years, progressing to greater control in the adult 2 stage, but with less need for pruning. The use of deficit strategies resulted in considerable water savings and crop evapotranspirati on coefficients are proposed for practical adoption of the strategies.
Chapter 4 analyses the effects on yield and its components and on oil production.
Tree burden and fat yield were the parameters most affected by the treatments:
reducing water supply reduced load but increased fat content, except in situations of
very seve re deficit. The RDC 1 treatment maintained the same level of production as the control at all the stages studied. At adult stage 2, production, mainly oil, was similar in all treatments. The application of regulated deficit irrigation strategies led to an increase in water use efficiency in the adult’s s tages the lower the water input, the greater the increase.
In chapter 5, the characteristics of the oils of the 4 treatments of the first two stages were studied. The physico chemical parameters did not reveal any differences between the treatments, and they were all classified as "extra virgin". The fatty acids
vary when the hedgerow is young and oleic acid can increase and that moderate and
severe strategies increase the phenols and pigments contents and, therefore, the stability of the oils, their nutritional value and improve the organoleptic characteristics.
Keywords:
Arbequina, super intensive , stem water potential, regulated deficit
irrigation, olive oil quality.
... Therefore, it requires more attention [22]. In contrast, E s is generally considered to be a water consumption that has no effect on yield formation and should be reduced as much as possible through plant management practices [23], which can be achieved through agricultural land management, such as applying mulch and using appropriate irrigation techniques [24]. T r is significantly affected by microclimate and often correlates well with solar radiation, vapor pressure deficit, and air temperature, provided that soil moisture is sufficient [25]. ...
Accurate information regarding crop evapotranspiration (ETc) and its components is essential for proper water management. Salinity has become increasingly serious in many parts of the world, affecting the use of saline water in irrigation for various biochemical processes, hence the importance of understanding the effects of soil and water salinity on ETc. This study aimed to determine the transpiration (Tr) and soil evaporation (Es) components that constitute ETc in tomatoes irrigated by drip irrigation and to investigate the effects of irrigation water salinity levels on ETc and its components, as well as on the crop coefficient (Kc) used to determine ETc. In addition, the reference evapotranspiration (ETo) values determined by the measurements obtained with the lysimeter system were compared with the ETo values calculated using the Almeria (ETo_Alm), FAO Radiation (ETo_FAO-Rad), and Hargreaves (ETo_Harg) models. During the spring growing period of 2022, tomatoes were cultivated under four different irrigation water salinity levels: S0 = 0.7 (control), S1 = 2.5 (low), S2 = 5.0 (medium), and S3 = 7.5 (high) dS m⁻¹. The Tr values in S0, S1, and S2 treatments were measured by the sap flow method. Radiation-based ETo prediction models had strong relationships with lysimeter-measured ETo values (R² > 0.977 and RMSE < 0.53 mm). The results indicated that increasing salinity levels led to a decrease in both Tr and ETc while causing an increase in Es. In the S0, S1, and S2 treatments, Es accounted for 16.3, 45.0, and 36.2%, respectively. Actual Kc values also decreased with increasing salinity. The results indicate that different actual Kc values can be used when calculating evapotranspiration in decision-making processes in greenhouse tomato production in Antalya and when irrigation water with different salinity levels is used. Additionally, actual ETc responses of tomatoes to salinity can be used to manage saline water in irrigation scheduling.
... When making macro-level decisions (like those involving the management of water and crops), particularly in rainfed agriculture, monitoring the geographical and temporal fluctuation of actual evapotranspiration of crops is helpful [1][2][3]. Variability in cropping is closely related to irregularity in rainfall in rainfed areas [4]. This type of research is critical for water-stressed areas because evapotranspiration is a major factor in drought and water-balance assessments [4][5][6][7]. ...
Satellite-derived evapotranspiration (ETa) products serve global applications, including drought monitoring and food security assessment. This study examines the applicability of ETa data from two distinct sources, aiming to analyze its correlation with crop yield (rice, maize, barley, soybean). Given the critical role of crop yield in economic and food security contexts, monthly and yearly satellite-derived ETa data were assessed for decision-makers, particularly in drought-prone and food-insecure regions. Utilizing QGIS, zonal statistics operations and time series graphs were employed to compare ETa with crop yield and ET anomaly. Data processing involved converting NRSC daily data to monthly and extracting single-pixel ET data using R Studio. Results reveal USGSFEWS as a more reliable ETa source, offering better accuracy and data continuity, especially during monsoon seasons. However, the correlation between crop yield and ETa ranged from 12% to 35%, while with ET anomaly, it ranged from 35% to 55%. Enhanced collection of satellite-based ETa and crop-yield data is imperative for informed decision-making in these regions. Despite limitations, ETa can moderately guide decisions regarding crop-yield management.
... Semi-physical methods, such as the Penman-Monteith method [7], are also widely used for ET estimation, especially for reference ET [8]. In addition, methods based on field observations, such as weighing evapotranspiration meter, water balance, and trunk sap flow methods, are used to estimate local ET, but cannot cover the whole watershed [9][10][11]. With the development of remote sensing technology, ET estimation methods based on remotely sensed data have become increasingly popular [12]. ...
The validation of remotely sensed evapotranspiration (ET) products is important for the development of ET estimation models and the accuracy of the scientific application of the products. In this study, different ET products such as HiTLL, MOD16A2, ETMonitor, and SoGAE were compared using multi-source remote sensing data and ground-based data to evaluate their applicability in the Heihe River Basin (HRB) during 2010–2019. The results of the comparison with the site observations show that ETMonitor provides a more stable and reliable estimation of ET than the other three products. The ET exhibited significant variations over the decade, characterized by a general increase in rates across the HRB. These changes were markedly influenced by variations in land use and topographical features. Specifically, the analysis showed that farmland and forested areas had higher ET rates due to greater vegetation cover and moisture availability, while grasslands and water bodies demonstrated lower ET rates, reflecting their respective land cover characteristics. This study further explored the influence of various factors on ET, including land use changes, NDVI, temperature, and precipitation. It was found that changes in land use, such as increases in agricultural areas or reforestation efforts, directly influenced ET rates. Moreover, meteorological conditions such as temperature and precipitation patterns also played crucial roles, with warmer temperatures and higher precipitation correlating with increased ET. This study highlights the significant impact of land use and climatic factors on spatiotemporal variations in ET within the HRB, underscoring its importance for optimizing water resource management and land use planning in arid regions.
... where K d is the crop density coefficient, K cb full is the estimated basal K cb for peak plant growth conditions having nearly full ground cover (LAI > 3), and K c min is the minimum K c for bare soil (K c = 0.15 for standard agricultural conditions) [66,67]. K d presented in Equation (5) is calculated using the following equation [16]: ...
A two-year experiment was conducted with a local maize hybrid under full (F) and deficit (D) drip irrigation and rainfed conditions (R) to estimate maize evapotranspiration in Bosnia and Herzegovina (BiH). Three approaches, namely, A&P, SIMDualKc (SD), and vegetation index (VI), to estimate the actual crop coefficient (Kc act), the actual basal crop coefficient (Kcb act), and the actual crop evapotranspiration (ETc act), were applied with the dual crop coefficient method and remote sensing (RS) data for the first time. While Kcb act from all approaches matched FAO56 tabulated values, SD showed differences in comparison to A&P of up to 0.24 in D and R conditions, especially in the initial and mid-season stages. VI demonstrated very good performance in all treatments. In F, the obtained Kc act for all approaches during the initial and end stages were higher than the tabulated values, ranging from 0.71 to 0.87 for the Kc ini act and from 0.80 to 1.06 for the Kc end act, while the mid-season period showed very good agreement with the literature. The maize crop evapotranspiration range is 769–813 mm, 480–752 mm, and 332–618 mm for F, D, and R, respectively. The results confirmed the suitability of both approaches (SD and VI) to estimate maize crop evapotranspiration under F, with the VI approach demonstrating an advantage in calculating Kcb act, Kc act, and ETc act values under water stress conditions. The higher observed yields (67.6%) under irrigation conditions emphasize the need to transition from rainfed to irrigation-dependent agriculture in BiH, even for drought-resistant crops like maize.
... The value of the K c coefficient is not always the same for the same crop and varies depending on the stage of development the plant is in. To obtain more accurate results, FAO-56 determines two approximations to determine ET c , which are the simple approximation and the Dual Crop Coefficient (DCC) approximation [56,57]. ...
Agriculture being an essential activity sector for the survival and prosperity of humanity, it is fundamental to use sustainable technologies in this field. With this in mind, some statistical data are analyzed regarding the food price rise and sustainable development indicators, with a special focus on the Portugal region. It is determined that one of the main factors that influences agriculture’s success is the soil’s characteristics, namely in terms of moisture and nutrients. In this regard, irrigation processes have become indispensable, and their technological management brings countless economic advantages. Like other branches of agriculture, the wine sector needs an adequate concentration of nutrients and moisture in the soil to provide the most efficient results, considering the appropriate and intelligent use of available water and energy resources. Given these facts, the use of renewable energies is a very important aspect of this study, which also synthesizes the main irrigation methods and examines the importance of evaluating the evapotranspiration of crops. Furthermore, the control of irrigation processes and the implementation of optimization and resource management models are of utmost importance to allow maximum efficiency and sustainability in this field.
Evapotranspiration (ET) is an essential agroclimatic variable, fundamental for estimating crop water requirements and managing irrigation. However, quantifying ET has been challenging due to limited monitoring stations, leading to the development of alternative methods, including the use of datasets and gridded products derived from satellite remote sensing or reanalysis of global models. Despite its complexity, the FAO-Penman Monteith reference evapotranspiration (ET0) model is widely used, but challenges arise in upscaling it over extensive areas, especially where data are insufficient or heterogeneous as in the Colombian Thornthwaite regions. Datasets from platforms such as TERRACLIMATE, NASA POWER, and DMETREF-EUMETSAT provide valuable information for estimating ET0 at different spatial and temporal resolutions; however, there are limitations in terms of their coverage and accuracy. In this study, the ET0 derived from these three satellite-based datasets were compared with the monthly ET0 estimated from national legacy data from the available IDEAM weather stations (1981–2020) in Colombia, using robust linear estimators for the entire country. Results show that TERRACLIMATE (R² = 0.75, RMSE = 311 mm) performs better than NASA POWER (R² = 0.5, RMSE = 531 mm) and DMETREF-EUMETSAT (R² = 0.20, RMSE = 1666 mm) using Ordinary Least Squares regression, particularly in certain Thornthwaite regions. However, challenges remain, especially in arid areas, where the analyzed datasets show lower accuracy. The results of this study suggest that using certain ET data and gridded products, particularly TERRACLIMATE, is an effective approach for characterizing and monitoring this important agroclimatic variable.
This article develops a dynamic systems model for the sustainable management of water resources in the Tajan watershed. Initially, a dynamic systems model was developed and validated using VENSIM software. Subsequently, a model called PySD was developed using the Python programming language. The primary objective of this model is to predict the amount of water allocated from the watershed's resources to various sectors, including drinking, industry, agriculture, and the environment, as well as to estimate potential shortages. The validation results indicate that the PySD model can simulate water allocation with acceptable accuracy. The PySD model was then used to investigate the water resources and consumption in the Tajan watershed. The results showed that while drinking and environmental needs are almost fully met, the agricultural sector faces significant shortages. In particular, crops such as wheat, corn, and oilseeds experience more severe water shortages. In contrast, crops such as citrus, melons, and oilseeds in some areas have relatively good stability in water supply. Finally, the article evaluates the efficiency of the water resource system in meeting agricultural needs using various sustainability criteria. The results indicate that adopting specific management strategies, such as changing cropping patterns, determining optimal irrigation depths, and using alternative water resources, is necessary to improve the water resource situation in the Tajan watershed.
The 10th International Symposium Monitoring of Mediterranean Coastal Areas: problems and measurements techniques was organized by CNR-IBE in collaboration with Italian Society of Silviculture and Forest Ecology , and Natural History Museum of the Mediterranean and under the patronage of University of Florence, University of Catania, Accademia dei Lincei, Accademia dei Geogofili, Italian Association of Physical Geography and Geomorphology, Tuscany Region, The North Tyrrhenian Sea Ports System Authority, Livorno Municipality and Livorno Province. This edition confirmed the Symposium as the international occasion to present the research carried out in recent years on the monitoring of the Mediterranean Coastal Areas and therefore as a space to present new proposals and promote actions for the protection of the marine and coastal environment. In the Symposium, Scholars had illustrated their activities and exchanged innovative proposals, with common aims to promote actions to preserve coastal marine environment. In this 10th edition, in fact, we had more than 130 participants from 16 countries; this is a sign of great success and willingness to be presence in Livorno to discuss problems and propose solutions for the Mediterranean coastal areas.
Plan Predial (planpredial.inia.cl) is an interactive platform for La Araucanía region, Chile, which allows the user to efficiently plan the use of available property resources by generating technical–economic information that facilitates decision-making in a productive system. The need for its construction arises from permanent consultations from producers and technicians in the horticultural sector. It is free to access, which seeks to answer what, how much, when and how to produce, in different agricultural areas. For the development, technical information from primary and secondary sources in thirty-two species were considered. Models according to agro-ecological zone, crop rotation, history of production, harvest timing, sales format, crop yield, water demand, price series, resources, reinvestment, and start of work. Field validations were carried out for varieties, growing time and labour costs. A total of hundred fifty-six agronomic management alternatives were generated, combining the previous variables. The platform was built, to which extension agents and farmers can freely access as users to plan their production systems. This platform optimizes in real time, and delivers suggestions for crop management options, which contain the activities to be carried out in each stage of crop production, the minimum area to be cultivated, the Gantt chart with dates and duration of each activity, direct and indirect costs, and gross margin. With all this information, the minimum productive economic unit (UEMP) is obtained, expressed as an area from which profits are generated. It can be accessed from a computer or mobile device, through a browser. For its development, the CentOS 7 Operating System, JAVA 1.7, Tomcat 7 servlet container, PostgreSQL Database 9.6 and Matlab R2015a (Matlab Compiler Runtime) were used. Optimization was implemented in MATLAB, specifically, using the MILP intlinpro mixed-integer programming function, which searches for the minimum of a specific problem subject to certain restrictions.
The Barossa and Eden Valleys are renowned viticultural regions which produce premium wines. Water availability and security are the major impediments in long-term sustainable production of their irrigated vineyards. Apart from a hot and dry climate and low water allocation, quality of native and imported water resources in the Barossa region is declining which will potentially have severe adverse impact on the soil and irrigated industries. The climate-soil-crop continuum-based estimation of irrigation requirements is the most efficient way of applying appropriate amount of water to maintain long-term sustainability for this irrigated cropping system. It not only computes the correct amount of water but also helps in restricting off-site movement of water and maintains a congenial environment in the rootzone.
In the current study, six prominent and widely distributed soil types (sand over clay, SOC; shallow soil on rock, SSR; cracking clay soil, CCS; hard red brown soil, HRB; calcareous and gradational soil, CGS; acid and shallow soil on rock, ASR) were identified in the Barossa and Eden Valley regions to evaluate the irrigation requirement and water quality induced risks under different irrigation water sources. Representative local soil, climate, crop, and irrigation system design specific parameters were gathered from selected study sites. Water demand for irrigated vineyards was estimated for the Barossa and Eden Valley regions separately following FAO-56 dual crop coefficient approach for major soil types under the current climate (2000-2023). Subsequently, the long-term (2023-24 to 2050-51) impact of use of various available irrigation water sources in the Barossa region was evaluated in different soils under the median climate change prediction (RCP 4.5) data (NARCliM 1.5) employing multi- component major ion chemistry model HYDRUS-UNSATCHEM. The model was equilibrated with the measured soil solution and exchange parameters for 72 years (1951- 2023) to achieve a quasi-equilibrium state for soil solution and ion exchange behaviour of different soils. Available water quality sources tested are BIL (Barossa Infrastructure Limited) water (Bw), SA water supply (SAw), blended BIL water (Bbw), recycled water (Rew) from Bolivar, and groundwater (Gw) with wide range of salinity (0.35- 3.3 dS/m) and chemical composition (SAR, 3.3- 11.1). A total of 56 scenarios were tested to evaluate the impact of various quality water sources used for irrigation on six soil types (SOC, SSR, CCS, HRB, CGS, ASR) and sustainable management options were explored under four soil indicators i.e., pH, ECsw, SAR and ESP and relative yield reduction in response to rootzone salinity.
Model projections demonstrated that the irrigation requirement of vineyards varied with climate and soil types. In the Barossa Valley region, average annual irrigation requirement varied from 111- 184 mm with a regional average of 136 mm, being higher for sand over clay and calcareous gradational soils and lower for hard red brown and cracking clays. Similar patterns of the average annual irrigation requirement in different soils was observed in the Eden Valley region, however the annual irrigation varied from 79- 157 mm with an average of 103 mm. Annual regional irrigation demand estimated for the cropped area and soil type distribution in the Barossa and Eden Valley was highly correlated with annual (R2 = 0.71- 0.72) and in-season (R2 = 0.76- 0.77) rainfall and showed large year to year variability. Average annual demand over the 23 years for Barossa and Eden was 14.22 Gl/year and 2.04 GL/year, respectively.
Long-term risk assessment (2023-24 to 2050-51) of different quality irrigation waters were performed and model simulations showed that BIL, SA water and blended (15% of CWMS, Community Wastewater Management Scheme) BIL water maintained the rootzone soluble salts (ECsw, 2- 4.5 dS/m) close to the grapevine tolerance threshold (ECsw = 4.2 dS/m) in all soil types over 28 years of irrigation. In heavy textured soils such as cracking clays rootzone salinity of 4.2 dS/m (average tolerance threshold) can have adverse impact on grapevines. Soil solution salinity (ECsw) in different soils was in the order (low to high) ASR > HRB > CGS > SOC > SSR >CCS. Maximum amounts of salts are deposited in the deeper part of the soil profile (1m). Other water sources such as recycled water (EC = 1.8 dS/m) and groundwater (EC = 3.3 dS/m) were observed to increase the ECsw > 10 dS/m, especially at the lower depths of soil profile after 5-10 years of irrigation in the Barossa Valley. In the Eden Valley, irrigation water salinity of 3.3 dS/m (groundwater), maintained the soil solution salinity in the ASR soils below the impact threshold for grapevines signifying the importance of high rainfall induced natural leaching in the soil. Soil pH showed a marginal response to the quality of irrigation water and remained within 7.5- 8.6 range in all the soils and under all irrigation water qualities.
Relative grapevine yield reductions were estimated for the irrigation induced average rootzone salinity developed over 28 years of irrigation with different qualities of irrigation waters. Grapevine yield was reduced by 2.9- 11.5 and 11- 23%, respectively with recycled water and groundwater irrigation. The relative grapevine yield reduction in response to Rew and Gw irrigation in different soils was in the order (high to low) as CCS > SSR > CGS > SOC > HRB. No yield reductions were expected under BIL, SA water and blended BIL water irrigation as the average rootzone salinity remained below the average tolerance threshold (ECsw = 4.2 dS/m).
The irrigation water quality induced sodicity hazard in terms of increased SARsw and ESP was estimated in all the soils. Rapid SAR (high sodium levels compared to Ca and Mg) and ESP development was modelled in all soil types and with all irrigation water qualities including BIL and SA water. Soil solution SAR (SARsw) under BIL water (4-8) had the potential to increase the exchangeable sodium percentage (ESP) more than the threshold level (6%) for soil degradation. Maximum levels of average rootzone SARsw were observed under groundwater irrigation which varied from 6.5- 18 mmol/L1/2 in different soils. Comparatively, cracking clay (CCS) and acid soil on rocks (ASR) showed lower SARsw and ESP values than sand over clay (SOC), calcareous and gradational (CGS) and hard red brown (HRB) soils. The impact of high SARsw on ESP development was rapid in sand textured SOC soil while it was slow in cracking clay (CCS). The maximum level of ESP development was observed under groundwater irrigation ranging from 13.8- 52.0% followed by Rew irrigation (13.9- 31.7%). The ESP development with all other irrigation waters ranged between 3.8- 28.4%.
The critical level of SARsw to exceed the threshold ESP (6%) was estimated for the range of soil types. The average relationship between SARsw and ESP across different soils show that an SARsw of 2.1 can develop an ESP higher than the soil dispersion threshold (6%) in the Barossa region. Similarly, for individual soils an SARsw of 1.7, 3.3, 3.3, 1.2, 3.4 and 0.9, respectively for SOC, SSR, CCS, HRB, CGS and ASR soil was found to develop an ESP more than threshold for soil degradation. Low values for ASR, HRB and SOC soils were related to high ESP at the initial stage at lower soil depths.
Model simulations were performed to investigate options to ameliorate the salinity hazard posed by the long-term use of brackish water. Annual leaching irrigation of 30 mm in spring (early September) with good quality water (BIL) and subsequent irrigation with recycled water (1.8 dS/m) or groundwater (3.3 dS/m) reduced the ECsw below the grapevine tolerance threshold in the upper 40- 50 cm soil. Application of two 30 mm irrigations within a fortnight in September pushed the salts deeper in the soil profile. Salts remained high at lower depths especially in SOC, CCS, and CGS soils.
Model predictions revealed that leaching irrigation alone are not sufficient to ameliorate the irrigation induced high sodicity hazard in the soil solution (SARsw) and on the soil exchange (ESP). The appropriate amount of ameliorant such as gypsum should be applied in along with leaching irrigation to reduce the sodicity hazard which is an inherent character of soil minerology of most of the Barossa and Eden Valley region soils. Previous simulation suggest that the annual gypsum application of 1.7 and 4.3 t/ha can reduce the ESP in sand over clay soil by 20 and 50%, respectively. This application was less effective in other soil types especially heavy textured soils.
Modelling predictions in the current study improved our understanding of the fragile production system for irrigated vineyards in the Barossa and quality of available water resources has the potential to greatly impact on crop yield and soil health indicators. Management options such as leaching irrigation and annual gypsum application are crucial for enhancing the long-term sustainability of vineyards; but maintaining a secure source of good quality water is important to support the wine industry in this region.
The significance of crop evapotranspiration (ETa) to climate science, agronomic research, and water resources is not in dispute. What continues to draw attention is how variability in ETa is driven by changing environments, abiotic stresses, and management practices. Here, the impacts of elevated CO2 concentration (e[CO2]), elevated ozone concentration (e[O3]), warming, abiotic stresses (water, salinity, heat stresses), and management practices (planting density, irrigation methods, mulching, nitrogen application) on cropland ETa were reviewed, along with their possible causes and estimation. Water and salinity stresses, e[O3], and drip irrigation adoption generally led to lower total growing–season ETa. However, total growing–season ETa responses to e[CO2], warming, heat stress, mulching, planting density, and nitrogen supplement appear inconsistent across empirical studies. The effects of e[CO2], e[O3], water and salinity stresses on total growing–season ETa are attributed to their influence on stomatal conductance, root water uptake, root and leaf area development, microclimate, and potentially phenology. Total growing–season ETa in response to warming is affected by variations in ambient growing–season mean air temperature and phenology. The differences in crop ETa under varying planting densities are due to their differences in leaf area. The responses of ETa to heat stress, mulching, and nitrogen application represent trade–off between their opposite effects on transpiration and evaporation, along with possibly phenology. Modified ETa models currently in use can estimate the response of ETa to the many aforementioned factors except for e[O3], heat stress, and nitrogen application. These factors offer a blueprint for future research inquiries.
Around 15% of India's GDP comes from agriculture, which is the foundation of the country's economy. India's economic development and efforts to combat poverty have already benefited greatly from its agricultural sector. Sustainable management of water resources can increase agricultural productivity. The study performed in the Paliganj distributary is a part of the Sone canal system in south Bihar, India. The Paliganj distributary command area lies wholly in the Gangetic plain. The estimation of crop evapotranspiration is carried out using the modified Penman–Monteith equation for the period 1980–2015. The crop coefficient of the crops has been estimated by using a single crop coefficient and a dual crop coefficient. The crop water requirement, irrigation water requirement, and irrigation scheduling of crops grown in the study area are determined using CROPWAT 8.0 software. The results conclude that the maximum, minimum, and average values of ET0 were found to be 7.65, 1.31, and 3.86 mm/day, respectively. The crop water requirement and irrigation requirement of crops grown in kharif, rabi, hot weather, and annual seasons in the study area were lower by using dual crop coefficient.
Drought stress is a major production constraint of groundnut in Africa and Asia where it is largely grown as rainfed crop. The experiments aim to design an early testing approach for drought tolerance in the groundnut breeding pipeline to ensure sustainable production. A population of 600 multi parent advanced generation inter-cross (MAGIC) lines (MLs) (F 8/9 generation) and 100 advance breeding lines (ABLs) were studied in LeasyScan, a high throughput phenotyping platform (HTPP) to assess early canopy growth, and under a managed stress environment (MSE). MSE ensures uniform water application in well-watered and water-stressed plots, while intermittent drought is imposed in water-stressed plots from 1000 ⁰ cumulative thermal time (CTT) during pod-filling stage. Digital biomass, leaf area 3D and plant height measured under HTPP recorded high heritability along with high genetic gain and were identified for use as selection criteria for early canopy vigour. The second selection criteria is Mean Score Index (MSI) (1 to 10 scale), which accounts for both resilience and productivity capacity indices (RCI and PCI), with the MSI ranging from 1.4 to 8.4. Based on results, a two-step selection approach is proposed for selection of traits required for adaption under drought stress. The approach involves HTPP (LeasyScan) to select early canopy vigour followed by selection based on MSI under MSE. MSE is field based and expensive, hence screening of a large number of selection candidates under HTTP helps to select a relatively small subset of early vigour lines for screening under MSE for agronomic performance.
Accurate quantification of evapotranspiration (ET) and its bifurcation into productive transpiration (T) and unproductive evaporation (E) are essential for the successful implementation of sustainable irrigation practices. This study compares the performances of three distinct methods for partitioning ET into E and T fluxes from flood‐irrigated rice fields. These methods include: i) the FAO dual Kc‐ETo model, which utilizes Penman–Monteith (PM) estimates of reference ET and crop‐specific scaling factors; ii) the Priestley‐Taylor (PT) method, which relies on radiation‐driven energy balance at the canopy surface; and iii) the flux variance similarity (FVS) method, which utilizes high‐frequency eddy covariance (EC) measurements of carbon and water vapour fluxes. Meteorological, phenological and hydrological parameters were monitored over two winter seasons in a paddy field, replicating site‐specific management strategies. The cumulative ETs obtained from the PM, PT and FVS methods were 445 mm, 300 mm and 356 mm, respectively, for season 1 and 428 mm, 321 mm and 375 mm, respectively, for season 2. The accuracy of the ET estimation and partition methods was assessed against independent measurements of ET and E using a lysimeter and a microlysimeter. The results demonstrated that the EC‐based FVS method offers superior accuracy in both quantifying (R ² = 0.67, RMSE = 0.70 mm) and partitioning (R ² = 0.51, RMSE = 0.76 mm) ET fluxes, followed by the PM‐based FAO dual Kc‐ETo and PT methods. Evaporation accounted for 29 ± 5% of consumptive water use, highlighting an opportunity for the implementation of water‐saving strategies, particularly during vegetative and transplantation stages. The findings of the path analysis indicate that vegetative and radiation factors influence ET variation, while meteorological and soil factors significantly impact T variation.
Irrigation agriculture plays a valuable role in upholding sustainable food security by enhancing agricultural production. Uneven distribution and shortage of rainfall has resulted in unsustainable food production, leading to food insecurity in Ethiopia. The establishment of irrigation development strategies may have a significant role in reducing the risk posed by uneven distribution of rainfall. This study aims to map suitable land for surface irrigation development in the Abay Basin of the Andassa watershed, Ethiopia, based on a GIS-based multicriteria evaluation (MCE) technique. Biophysical factors (land use and land cover, soil, slope, and river proximity) that significantly affect surface irrigation suitability were considered. Each of these was processed and analyzed for its potential contribution to surface irrigation suitability on a pixel-by-pixel basis. The factors were weighted using a pairwise comparison matrix, and weights were combined using weighted overlay analysis. The analysis results indicated that approximately 60% of the watershed land was highly (9%) and moderately (51%) suitable for surface irrigation. Slope and river proximity were the major limiting factors during the suitability assessment. Of the 60% of suitable land, 70% could be irrigated with the water resource potential of the Andassa River. The remaining 30% of the area needs other means of water harvesting techniques. Future works need to consider soil chemical properties as a determining factor for surface irrigation suitability since this study did not consider these properties as a factor in the overlay analysis.
Climate change poses significant threats to agriculture, including food security, livelihoods and economic growth. Based on the importance of cocoa, there is a need for sustainable crop production and resilience to anticipated changes in rainfall and temperature in the future. Irrigation is an important climate-smart practice for alleviating abiotic stress and enhancing crop productivity, and irrigation is seldom practiced in the cacao orchards of West Africa. Studies were conducted to examine the effects of dry season gravity drip irrigation on the rootzone moisture, tree water use (evapotranspiration), leaf area index and yield of cacao in a rainforest zone of Nigeria. Irrigation treatments were based on water application at 5- and 10-day intervals and 50, 70 and 100% Pan evaporation, which was applied using point source emitters on drip lines. The soil moisture content, photosynthetic active radiation, leaf area index and extinction coefficient differed among the irrigation treatments. Deficit irrigation (10-day and 50% EPan) enhanced water use efficiency by 25–44% (30 and 50% water savings), while full irrigation enhanced soil moisture, cacao ET, and pod and bean yields. This study established irrigation and water requirements for cacao in the dry season and confirmed the relevance of irrigation for enhanced cacao performance and climate mitigation.
This paper evaluates how well the FAO-56 style soil water evaporation model simulates measurements of evaporation (E) from bare soil. Seven data sets were identified from the literature and in all but one case. the individuals who took the measurements were contacted and they provided the writers with specific weather and soils data for model input. Missing weather and soils data were obtained from online sources or from the National Climatic Data Center. Simulations for three possible variations of soil data were completed and compared. The measured and the FAO-56 simulated E/ETo and cumulative evaporation trends and values were similar. Specifically. the average evaporation weighted percent difference between the measured and the simulated cumulative evaporation was between -7.5 and -0.5%. This evaluation suggests model accuracy of about +/-15% with the use of sound weather data and a fairly generalized understanding of soil properties in the location being evaluated.
A model is presented that uses a daily mean evapotranspiration ETo rate to estimate energy-limited (potential or Stage 1) soil evaporation, and it also uses daily mean ETo and a soil hydraulic beta factor to estimate soil hydraulic property-limited (Stage 2) evaporation. The model provides good estimates of cumulative soil evaporation on both hourly and daily bases when compared to observed soil evaporation in three field trials. Crop coefficient K-c values from cumulative hourly and cumulative daily soil evaporation estimates and ETo data were comparable. Using a soil hydraulic factor (beta = 2.6) in the model gave a fair approximation for the widely used K-c curves for initial growth of crops presented in the United Nations Food and Agricultural Organization's irrigation and Drainage Paper 24. However, using a site-specific beta factor should improve soil evaporation and K-c estimates for site-specific applications.
A model is presented for calculating the daily evaporation rate from a
crop surface. It applies to a row crop canopy situation in which the
soil water supply to the plant roots is not limited and the crop has not
come into an advanced stage of maturation or senescence. The crop
evaporation rate is calculated by adding the soil surface and plant
surface components (each of these requiring daily numbers for the leaf
area index), the potential evaporation, the rainfall, and the net
radiation above the canopy. The evaporation from the soil surface
Es is calculated in two stages: (1) the constant rate stage
in which Es is limited only by the supply of energy to the
surface and (2) the falling rate stage in which water movement to the
evaporating sites near the surface is controlled by the hydraulic
properties of the soil. The evaporation from the plant surfaces
Ep is predicted by using an empirical relation based on local
data, which shows how Ep is related to Eo through
the leaf area index. The model was used to obtain the total evaporation
rate E = Es + Ep of a developing grain sorghum
(Sorghum bicolor L.) canopy in central Texas. The results agreed well
with values for E measured directly with a weighing lysimeter.
VAPOTRANSPIRATION (ET) data for irri- 1.7.1 gated crops in southern Idaho were used to de- velop relationships for estimating net radiation and potential ET for the USDA-ARS Computerized Irri- gation Scheduling Program. ET estimated with the initial relationships compared well with recent mea- surements obtained with two sensitive weighing lysim- eters. The:average daily measured Et for alfalfa for 128 days when there was full cover was 7.23 mm, while the average daily estimated ET was 7.15 mm. Crop curve relationships were developed from the ET results for snap beans (Phaseolus vulgaris L). The depletion of soil water was predicted for two years of irrigated beans with the scheduling program using the improved crop curves and compared with the mea- sured as a test of its performance. The standard devia- tion of the difference between predicted and measured was about 0.95 mm/day from planting until harvest. The results also demonstrated the importance of ob- taining -representative meteorological data for irrigation scheduling.
TREMENDOUS international scientific
effort has been expended on
evaporation and transpiration problems
during the past decade as evidenced
by hundreds of technical publications,
and numerous conferences. However,
use of this scientific achievement by
agriculturalists, project planners and
operators of irrigation farms has lagged
behind technological advancements.
The lag in adaptation of new technology
by the user can be partly attributed
to a lack of time, technical
training and experience in meteorology,
physics and agronomy
The Imperial Irrigation District is a large irrigation project in the western United States having a unique hydrogeologic structure such that only small amounts of deep percolation leave the project directly as subsurface flows. This structure is conducive to relatively accurate application of a surface water balance to the district, enabling the determination of crop evapotranspiration sETcd as a residual of inflows and outflows. The ability to calculate ET c from discharge measurements provides the opportunity to assess the accuracy and consistency of an independently applied crop coefficient—reference evapotranspiration sKc ET0d procedure integrated over the project. The accuracy of the annual crop evapotranspiration via water balance estimates was ±6% at the 95% confidence level. Calculations using Kc and ET0 were based on the FAO-56 dual crop coefficient approach and included separate calculation of evaporation from precipitation and irrigation events. Grass reference ET 0 was computed using the CIMIS Penman equation and ETc was computed for over 30 crop types. On average, Kc-based ET computations exceeded ETc determined by water balance (referred to as ETc WB) by 8% on an annual basis over a 7 year period. The 8% overprediction was concluded to stem primarily from use of Kc that represents potential and ideal growing conditions, whereas crops in the study area were not always in full pristine condition due to various water and agronomic stresses. A 6% reduction to calculated Kc-based ET was applied to all crops, and a further 2% reduction was applied to lower value crops to bring the project-wide ET predicted by Kc-based ET into agreement with ETc WB. The standard error of estimate (SEE) for annual ETc for the entire project based on Kc, following the reduction adjustment, was 3.4% of total annual ETc, which is considered to be quite good. The SEE for the average monthly ETc was 15% of average monthly ETc. A sensitivity analysis of the computational procedure for Kc showed that relaxation from using the FAO-56 dual Kc method to the more simple mean (i.e., single) Kc curve and relaxation of specificity of planting and harvest dates did not substantially increase the projectwide prediction error The use of the mean Kc curves, where effects of evaporation from wet soil are included as general averages, predicted 5% lower than the dual method for monthly estimates and 8% lower on an annual basis, so that no adjustment was required to match annual ET derived from water balance. About one half of the reduction in estimates when applying the single (or mean) Kc method rather than the dual Kc method was caused by the lack of accounting for evaporation from special irrigations during the off season (i.e., in between crops).
This article summarizes the essential definitions and methodologies for estimating crop water and irrigation requirements. The concept of reference evapotranspiration is assumed relative to a crop canopy such as grass but with constant crop characteristics. The hypotheses on which this approach is based are discussed relative to crop surface and aerodynamic resistances to heat and vapor fluxes. The crop evapotranspiration is defined using crop coefficients applied to the reference evapotranspiration, which reflect the canopy differences between the crop and the reference crop. Both time-averaged and dual-crop coefficients are explained, the first when the coefficients relative to crop transpiration and evaporation from the soil are summed and averaged for the crop-stage periods, the latter when a daily calculation of transpiration and evaporation coefficients is adopted. Corrections for climate and crop density are presented. Finally, essential information on the soil water balance to estimate crop irrigation requirements is provided.
The new crop coefficients are basal or minimal coefficients for conditions when soil evaporation is minimal but root-zone soil moisture is adequate. When combined with improved estimates of evaporation from wet soils, they should permit more accurate estimates of daily crop ET, more accurate irrigation scheduling, and more reliable estimates of crop water requirements. Curves were developed for alfalfa, potatoes, snap beans, sugarbeets, peas, sweet and field corn and winter and spring cereals. -from ASCE Publications Abstracts
A digital simulation model was developed to relate the numerous meteorologic, crop, and soil moisture relationships on a daily basis throughout the year. For those processes not yet adequately described for use in models, a rational representation was developed. The model details are presented and the results of applying the model to watersheds with either corn or grass crops from March through November for 3 yrs are discussed. The model was evaluated by comparing predicted and observed soil moistures.
Using existing antecedent moisture condition (AMC) Curve Number relationships, a general expression of rainfall-runoff is developed for AMC I and AMC III. The probability distribution of event runoff exceeding zero is found to be lognormal. Relative storm size is then proposed to be defined on the ratio P/S, where a "large" storm has P/S > 0.46, when 90% of all rainstorms will create runoff. Consequent problems arising in the definition of CN from rainfall-runoff data are discussed.
The significance of the soil surface moisture (thetas) with respect to daily bare soil evaporation (Ed) is analyzed using data from numerical simulations. This was performed by running a mechanistic model of heat and water flows in the soil. The mechanistic model was calibrated and validated on three different soils with contrasted hydraulic properties. Results show that thetas does not allow an accurate estimate of the ratio of Ed to the daily potential evaporation (Epd). Added variables such as Epd and the wind velocity are necessary to improve the prediction of the Ed/Epd ratio. In a second attempt, a simple model of Ed is proposed. It is based on three empirical parameters and required the measurement of thetas obtained at midday, Epd, and the daily wind velocity. For a given soil, a single set of the three parameters allows an accurate estimate of Ed under soil moisture and climatic conditions encountered through the year in temperature areas.
Recent developments in the study of moisture and heat fields in the soil
are applied to the problem of evaporation from bare soil surfaces. Most
of the analysis is confined to steady conditions, but it definitely
suggests that there are three phases to the desiccation of a given soil
profile:1. So long as the soil is sufficiently moist, the evaporation
rate, E, is indistinguishable from that from a saturated surface,
E3.2. At intermediate moisture contents, E is independent of
E3 and depends only on the soil-moisture distribution.3. When
the surface layers of the soil are sufficiently dry, E is sensitive to
the heat flux in the soil, and a negative correlation between E and
E3 may follow.The first and second of these correspond to the
well-known constant and falling rate phases of the `isothermal' drying
of initially saturated soils and other porous media, which thus receive
quantitative physical explanation. There is experimental evidence of the
existence of the third phase also.Other results of the article include
:1. Development of a (steady state) mode1 of the energy balance at
imperfectly evaporating surfaces (E < E3). This leads to a
simplified but suggestive approach to the microclimate of bare soils.2.
Analysis of the spatial distribution of evaporation sites within the
soil.3. Analysis of the modification of the energy balance which results
from the location of evaporation sites within the soil rather than at
the surface.
Evaporation from the soil (Es) in the areas wetted by emitters under drip irrigation was characterised in the semi-arid, Mediterranean climate of Crdoba (Spain). A sharp discontinuity in Es was observed at the boundary of the wet zone, with values decreasing sharply in the surrounding dry area. A single mean value of evaporation from the wet zone (Esw) was determined using microlysimeters. Evaporation from the wet zones of two drip-irrigated olive orchards was clearly higher than the corresponding values of Es calculated assuming complete and uniform soil wetting (Eso), demonstrating the occurrence of micro-scale advection in olive orchards under drip irrigation. Measurements over several days showed that the increase in evaporation due to microadvection was roughly constant regardless of location and of the fraction of incident radiation reaching the soil. Thus, daily evaporation from wet drip-irrigated soil areas (Esw) could be estimated as the sum of Eso and an additive microadvective term (TMA). To quantify the microadvective effects, we developed variable local advective conditions by locating a single emitter in the centre of a 1.5 ha bare plot which was subjected to drying cycles. Esw increased relative to Eso as the soil dried and advective heat transfer increased evaporation from the area wetted by the emitter. The microadvective effects on Es were quantified using a microadvective coefficient (Ksw), defined as the ratio between Esw and Eso. A model was then developed to calculate TMA for different environmental and orchard conditions. The model was validated by comparing measured Esw against simulated evaporation (Eso+TMA) for different soil positions and environmental conditions in two drip-irrigated olive orchards. The mean absolute error of the prediction was 0.53 mm day-1, which represents about a 7% error in evaporation. The model was used to evaluate the relative importance of seasonal Es losses during an irrigation season under Crdoba conditions. Evaporation from the emitter zones (Esw) represented a fraction of seasonal orchard evapotranspiration (ET), which ranged from 4% to 12% for a mature (36% ground cover) and from 18% to 43% of ET for a young orchard (5% ground cover), depending on the fraction of soil surface wetted by the emitters. Estimated potential water savings by shifting from surface to subsurface drip ranged from 18 to 58 mm in a mature orchard and from 28 to 93 mm in a young orchard, assuming daily drip applications and absence of rainfall during the irrigation season.
Prediction accuracy for project-wide evapo- 12 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING © ASCE / JANUARY/FEBRUARY 2005 rtranspiration using crop coefficients and reference evapotranspira-tion
- R G Allen
- A J Clemmens
- C M Burt
- K Solomon
- O Halloran
Allen, R. G., Clemmens, A. J., Burt, C. M., Solomon, K., and O’Halloran, T. (2005). “Prediction accuracy for project-wide evapo- 12 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING © ASCE / JANUARY/FEBRUARY 2005 rtranspiration using crop coefficients and reference evapotranspira-tion.” J. Irrig. Drain. Eng., 13(1), XXX XXX
Copyright ASCE. For personal use only; all rights reserved. transpiration using crop coefficients and reference evapotranspira-tion
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Irrigation scheduling for water and energy conservation in the 80's, ASAE
- J L Wright
Wright, J. L. (1981). "Crop coefficients for estimates of daily crop evapotranspiration." Irrigation scheduling for water and energy conservation in the 80's, ASAE, St. Joseph, Mich., 18-26.
Sharkey soils in Mississippi
- D E Pettry
- R E Switzer
Pettry, D. E., and Switzer, R. E. (1996). "Sharkey soils in Mississippi."
Mississippi Agricultural and Forestry Experiment Station Bulletin
1057 http://msucares.com/pubs/bulletins/b1057.htm, accessed October 17, 2003.
Méthode pratique de calcul des besoins en eau Traité d'irrigation
- L S Pereira
- M Smith
- R G Allen
Pereira, L. S., Smith, M., and Allen, R. G. (1998). " Méthode pratique de calcul des besoins en eau. " Traité d'irrigation, J. R. Tiercelin, ed., Lavoisier, Technique & Documentation, Paris, 206–231.
Estimation of crop evapotranspiration by means of the Penman-Monteith equation
- P J Vanderkimpen
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