Searching for Sustainable-Irrigation Issues of Clementine Orchards in the Syrian Akkar Plain: Effects of Irrigation Method and Canopy Size on Crop Coefficients, Transpiration, and Water Use with SIMDualKc Model

Citrus is one of the most valuable crops in Syria, with the largest production areas in the Tartus and Latakia provinces. Water-saving policies have been adopted to modernize the irrigation systems and increase water productivity. Following dedicated research, this study aimed to evaluate the water balance in clementine trees irrigated with diverse methods and schedules using the SIMDualKc software model. Two experiments are reported: one with 10–14 years old trees irrigated with different methods (20072011) and the other with the same trees but now 1820 years old, irrigated with different schedules (20152019). The SIMDualKc model successfully simulated the soil water contents measured in the various field plots, with root mean square error values lower than 0.004 m3 m3 and modeling efficiencies up to 0.83. The model-calibrated standard basal crop coefficients (Kcb) were approximately constant throughout all growing stages, assuming values of 0.540.55 for the mature trees having smaller height (h) and fraction of ground cover (fc), and 0.64 for older trees with larger canopies, i.e., larger h and fc. With drip irrigation, single Kc had a higher value (1.14) at the end, non-growing, and initial stages, and a lower value (0.75–0.76) during mid-season (Kc mid), because precipitation was lesser then, contributing less to soil evaporation. On the other hand, Kc values were nearly constant with micro-sprinkler and surface irrigation techniques because the ground was fully wetted. The Kcb values derived from the fraction of ground cover and height (A&P approach) were similar to those obtained from the model, thus showing that the A&P approach represents a practical alternative to estimate Kcb in the practice of irrigation management. The soil water balance further revealed a large weight of the terms corresponding to the non-beneficial water consumption and non-consumptive water use when the fraction wetted was large and the application efficiencies were low. These terms were reduced, namely, evaporation losses when drip irrigation was used. This study, thus, provides a valuable tool for improving the irrigation management, water saving, and water productivity of Syrian citrus production systemsinfo:eu-repo/semantics/publishedVersio

Modelling of soil water content and soil salinity with HYDRUS-1D

Mestrado em Engenharia Agronómica. Universidade de Lisboa, Instituto Superior de AgronomiaSalt-affected soils may result in highly negative impacts on the soils’ functions, limiting the soils’ productivity and ultimately leading to desertification. The area of salt-affected soils is increasing globally as a result of inadequate irrigation practices and of climate change. This work was carried out within the SoilSalAdapt project, which studies the hypothesis that adaptation of soil microbiome to soil salinity may result in increased crop tolerance. The aim of this work was to model the soils’ water content and soil salinity in the three different soils used in the experiment carried out by the project team at the Lincoln University, UK. In experiment, spinach was grown in vases, without fertilization, inside a polytunnel, during two growth cycles. Spinach was irrigated with non-saline water and, at the end of the second cycle, with highly-saline water. In this work, SIMDualKc was used to calculate crop evapotranspiration under standard conditions using the dual crop coefficient method. HYDRUS-1D was used to model the soil water content and electrical conductivity of soil water, integrating water and salinity stresses to obtain the actual crop evapotranspiration. The models resulted in a root mean square error between 0.024 and 0.063 cm3cm-3 for soil water content and between 1.74 and 3.31 dSm-1 for soil salinity. The errors were lower when considering only the first growth cycle. At the end of the second cycle, when saline water was applied, the models underestimated the water content and overestimated the salinity. These larger errors reflect the fact that observed data, which was measured with a TDR, overestimated the soil water content when soil salinity was high. The models obtained in this thesis will allow the simulation of soil salinity under short- and long-term conditions, considering different irrigation managements and future climate conditions, and the estimation of potential productivity losses.A salinidade pode afetar os solos resultando em impactos negativos nas funções do solo, limitando a sua produtividade e podendo levar à desertificação. A área afetada pela salinidade está a crescer mundialmente, resultado de uma gestão inadequada da rega e das alterações climáticas. Este trabalho foi feito no âmbito do projeto SoilSalAdapt, que estuda a hipótese de pré-adaptar o microbioma à salinidade do solo através da gestão da salinidade da rega, conferindo tolerância às culturas. O objetivo deste trabalho é modelar o teor de água do solo e a salinidade em três tipos de solo usados na experiência efetuada pela equipa da Universidade de Lincoln. Na experiência, espinafres cresceram em vasos dentro de uma estufa, sem fertilização, durante dois ciclos de crescimento. Foram regados com água não salina e no final do segundo ciclo com água extremamente salina. Foi usado o SIMDualKc para calcular a evapotranspiração cultural em condições padrão usando a metodologia dos coeficientes duais. O HYDRUS-1D foi usado para modelar o teor de água do solo e a condutividade elétrica da água do solo, integrando o stress salino e hídrico, para obter a evapotranspiração cultural real. A raiz do erro quadrático médio foi de 0,024 a 0,063 cm3cm-3 para o teor de água e entre 1,74 até 3,31 dSm-1 para a salinidade. Os erros foram mais baixos no primeiro ciclo quando comparados com o segundo. No final do segundo ciclo, quando a rega salina é aplicada, os modelos subestimam o teor de água do solo e sobrestimam a salinidade. Estes erros superiores devem-se aos dados medidos com o TDR, que sobrestimam o teor de água no solo quando a salinidade é elevada. Os modelos obtidos permitem simular a salinidade a curto e longo prazo, considerando diferentes gestões de regas e alterações climáticas, e estimar potenciais perdas de produtividade.N/

Prediction of crop coefficients from fraction of ground cover and height. Background and validation using ground and remote sensing data

ReviewThe current study aims at reviewing and providing advances on methods for estimating and applying crop coefficients from observations of ground cover and vegetation height. The review first focuses on the relationships between single Kc and basal Kcb and various parameters including the fraction of ground covered by the canopy (fc), the leaf area index (LAI), the fraction of ground shaded by the canopy (fshad), the fraction of intercepted light (flight) and intercepted photosynthetic active radiation (fIPAR). These relationships were first studied in the 1970’s, for annual crops, and later, in the last decennia, for tree and vine perennials. Research has now provided a variety of methods to observe and measure fc and height (h) using both ground and remote sensing tools, which has favored the further development of Kc related functions. In the past, these relationships were not used predictively but to support the understanding of dynamics of Kc and Kcb in relation to the processes of evapotranspiration or transpiration, inclusive of the role of soil evaporation. Later, the approach proposed by Allen and Pereira (2009), the A&P approach, used fc and height (h) or LAI data to define a crop density coefficient that was used to directly estimate Kc and Kcb values for a variety of annual and perennial crops in both research and practice. It is opportune to review the A&P method in the context of a variety of studies that have derived Kc and Kcb values from field measured data with simultaneously observed ground cover fc and height. Applications used to test the approach include various tree and vine crops (olive, pear, and lemon orchards and vineyards), vegetable crops (pea, onion and tomato crops), field crops (barley, wheat, maize, sunflower, canola, cotton and soybean crops), as well as a grassland and a Bermudagrass pasture. Comparisons of Kcb values computed with the A &P method produced regression coefficients close to 1.0 and coefficients of determination≥0.90, except for orchards. Results indicate that the A&P approach can produce estimates of potential Kcb, using vegetation characteristics alone, within reasonable or acceptable error, and are useful for refining Kcb for conditions of plant spacing, size and density that differ from standard values. The comparisons provide parameters appropriate to applications for the tested crops. In addition, the A&P approach was applied with remotely sensed fc data for a variety of crops in California using the Satellite Irrigation Management Support (SIMS) framework. Daily SIMS crop ET (ETc-SIMS) produced Kcb values using the FAO56 and A&P approaches. Combination of satellite derived fc and Kcb values with ETo data from Spatial CIMIS (California Irrigation Management Information System) produced ET estimates that were compared with daily actual crop ET derived from energy balance calculations from micrometeorological instrumentation (ETc EB).Results produced coefficients of regression of 1.05 for field crops and 1.08 for woody crops, and R2 values of 0.81 and 0.91, respectively. These values suggest that daily ETc-SIMS -based ET can be accurately estimated within reasonable error and that the A&P approach is appropriate to support that estimation. It is likely that accuracy can be improved via progress in remote sensing determination of fc. Tabulated Kcb results and calculation parameters are presented in a companion paper in this Special Issueinfo:eu-repo/semantics/publishedVersio

Estimation of actual crop coefficients using remotely sensed vegetation indices and soil water balance modelled data

A new procedure is proposed for estimating actual basal crop coefficients from vegetation indices (Kcb VI) considering a density coefficient (Kd) and a crop coefficient for bare soil. Kd is computed using the fraction of ground cover by vegetation (fc VI), which is also estimated from vegetation indices derived from remote sensing. A combined approach for estimating actual crop coefficients from vegetation indices (Kc VI) is also proposed by integrating the Kcb VI with the soil evaporation coefficient (Ke) derived from the soil water balance model SIMDualKc. Results for maize, barley and an olive orchard have shown that the approaches for estimating both fc VI and Kcb VI compared well with results obtained using the SIMDualKc model after calibration with ground observation data. For the crops studied, the correlation coefficients relative to comparing the actual Kcb VI and Kc VI with actual Kcb and Kc obtained with SIMDualKc were larger than 0.73 and 0.71, respectively. The corresponding regression coefficients were close to 1.0. The methodology herein presented and discussed allowed for obtaining information for the whole crop season, including periods when vegetation cover is incomplete, as the initial and development stages. Results show that the proposed methods are adequate for supporting irrigation managementinfo:eu-repo/semantics/publishedVersio

Modelling soil water dynamics of full and deficit drip irrigated maize cultivated under a rain shelter

Research PaperThe model HYDRUS-1D was used to simulate soil water dynamics of full and deficit irrigated maize grown under a rainout shelter during two crop seasons. Four irrigation treatments were established based on the amount of water applied to fulfil crop water requirements. Treatment D1 was irrigated to fully satisfy crop water requirements, while treatments D2 (mild deficit), D3 (moderate deficit), and D4 (severe deficit) were for increased controlled water stress conditions. The computation and partitioning of evapotranspiration data into soil evaporation and crop transpiration was carried out with the SIMDualKc model, and then used with HYDRUS-1D. The soil hydraulic properties were determined from numerical inversion of field water content data. The compensated root water uptake mechanism was used to describe water removal by plants. TheHYDRUS-1D model successfully simulated the temporal variability of soil water dynamics in treatments irrigated with full and deficit irrigation, producing RMSE values that varied between 0.014 and 0.025 cm3 cm 3 when comparing model simulations with field measurements. Actual transpiration varied between 224 and 483 mm. Potential transpiration reductions varied from 0.4 to 48.8% due to water stress, but plants were able to compensate for the water deficits in the surface layers by removing more water from the deeper, less stressed layers. HYDRUS-1D water balance estimates were also comparable with the corresponding ones determined with the SIMDualKc water balance model. Both modelling approaches should contribute to improve the webbased IRRIGA system, used to support farm irrigation scheduling in Brazilinfo:eu-repo/semantics/publishedVersio

Water use and yield of soybean under various irrigation regimes and severe water stress. Application of AquaCrop and SIMDualKc models

Data relative to two soybean seasons, several irrigation scheduling treatments, including moderate and severe deficit irrigation, and rain-fed cropping were used to parameterize and assess the performance of models AquaCrop and SIMDualKc, the latter combined with the Stewart’s yield model. SIMDualKc applies the FAO56 dual crop coefficient approach for computing and partitioning evapotranspiration (ET) into actual crop transpiration (Tc act) and soil evaporation (Es), while AquaCrop uses an approach that depends on the canopy cover curve. The calibration-validations of models were performed by comparing observed and predicted soil water content (SWC) and grain yield. SIMDualKc showed good accuracy for SWC estimations, with normalized root mean square error (NRMSE) 7.6%. AquaCrop was less accurate, with NRMSE 9.2%. Differences between models regarding the water balance terms were notable, and the ET partition revealed a trend for under-estimation of Tc act by AquaCrop, mainly under severe water stress. Yield predictions with SIMDualKc-Stewart models produced NRMSE < 15% while predictions with AquaCrop resulted in NRMSE 23% due to under-estimation of Tc act, particularly for water stressed treatments. Results show the appropriateness of SIMDualKc to support irrigation scheduling and assessing impacts on yield when combined with Stewart’s modelinfo:eu-repo/semantics/publishedVersio

Evapotranspiration and crop coefficients for a super intensive olive orchard. An application of SIMDualKc and METRIC models using ground and satellite observations

The estimation of crop evapotranspiration (ETc) from the reference evapotranspiration (ETo) and a standard crop coefficient (Kc) in olive orchards requires that the latter be adjusted to planting density and height. The use of the dual Kc approach may be the best solution because the basal crop coefficient Kcb represents plant transpiration and the evaporation coefficient reproduces the soil coverage conditions and the frequency of wettings. To support related computations for a super intensive olive orchard, the model SIMDualKc was adopted because it uses the dual Kc approach. Alternatively, to consider the physical characteristics of the vegetation, the satellite-based surface energy balance model METRIC™ – Mapping EvapoTranspiration at high Resolution using Internalized Calibration – was used to estimate ETc and to derive crop coefficients. Both approaches were compared in this study. SIMDualKc model was calibrated and validated using sap-flow measurements of the transpiration for 2011 and 2012. In addition, eddy covariance estimation of ETc was also used. In the current study, METRIC™ was applied to Landsat images from 2011 to 2012. Adaptations for incomplete cover woody crops were required to parameterize METRIC. It was observed that ETc obtained from both approaches was similar and that crop coefficients derived from both models showed similar patterns throughout the year. Although the two models use distinct approaches, their results are comparable and they are complementary in spatial and temporal scalesinfo:eu-repo/semantics/publishedVersio

Estimation of water use and crop coefficients for an intensive olive orchard using sap flow measurements and modeled data

Olive tree sap flow measurements were collected in an intensive orchard near Évora, Portugal, during the irrigation seasons of 2013 and 2014, to calculate daily tree transpiration rates (T_SF). Meteorological variables were also collected to calculate reference evapotranspiration (ETo). Both data were used to assess values of basal crop coefficient (Kcb) for the period of the sap flow observations. The soil water balance model SIMDualKc was calibrated with soil, biophysical ground data and sap flow measurements collected in 2013. Validated in 2014 with collected sap flow observations, the model was used to provide estimates of dual e single crop coefficients for 2014 crop growing season. Good agreement between model simulated daily transpiration rates and those obtained with sapflow measurements was observed for 2014 (R2=0.76, RMSE=0.20 mm d-1), the year of validation, with an estimation average absolute error (AAE) of 0.20 mm d-1. Olive modeled daily actual evapotranspiration resulted in atual ETc values of 0.87, 2.05 and 0.77 mm d-1 for 2014 initial, mid- and end-season, respectively. Actual crop coefficient (Kc act) values of 0.51, 0.43 and 0.67 were also obtained for the same periods, respectively. Higher Kc values during spring (initial stage) and autumn (end-stage) were published in FAO56, varying between 0.65 for Kc ini and 0.70 for Kc end. The lower Kc mid value of 0.43 obtained for the summer (mid-season) is also inconsistent with the FAO56 expected Kc mid value of 0.70 for the period. The modeled Kc results are more consistent with the ones published by Allen & Pereira [1] for olive orchards with effective ground cover of 0.25 to 0.5, which vary between 0.40 and 0.80 for Kc ini, 0.40–0.60 for Kc mid with no active ground cover, and 0.35–0.75 for Kc end, depending on ground cover. The SIMDualKc simulation model proved to be appropriate for obtaining evapotranspiration and crop coefficient values for our intensive olive orchard in southern Portugal

Transpiration and Water Use of an Irrigated Traditional Olive Grove with Sap-Flow Observations and the FAO56 Dual Crop Coefficient Approach

The SIMDualKc model was applied to evaluate the crop water use and the crop coefficient (Kc) of an irrigated olive grove (Olea europaea L.) located in Sicily, Italy, using experimental data collected from two crop seasons. The model applies the FAO56 dual Kc approach to compute the actual crop evapotranspiration (ETc act) and its components, i.e., the actual tree transpiration (Tc act), obtained through the basal crop coefficient (Kcb), and soil evaporation according to an evaporation coefficient (Ke). Model calibration was performed by minimizing the difference between the predicted Tc act and the observed daily tree transpiration measured with sap flow instrumentation (TSF field) acquired in 2009. The validation was performed using the independent data set of sap flow measurements from 2011. The calibrated Kcb was equal to 0.30 for the initial and non-growing season stages, 0.42 for the mid-season, and 0.37 for the end season. For both seasons, the goodness-of-fit indicators relative to comparing TSF field with the simulated Tc act resulted in root mean square errors (RMSE) lower than 0.27 mm d1 and a slope of the linear regression close to 1.0 (0.94 b0 1.00). The olive grove water balance simulated with SIMDualKc produced a ratio between soil evaporation (Es) and ETc act that averaged 39%. The ratio between actual (ETc act) and potential crop evapotranspiration (ETc) varied from 84% to about 99% in the mid-season, indicating that the values of ETc act are close to ETc, i.e., the adopted deficit irrigation led to limited water stress. The results confirm the suitability of the SIMDualKc model to apply the FAO56 dual Kc approach to tree crops, thus assessing the water use of olives and supporting the development of appropriate irrigation management tools that are usable by farmers. A different way to estimate Kcb is based on the approach suggested in 2009 by Allen and Pereira (A&P), which involves the measured fraction of ground covered (shaded) by the crop and the height of the trees. Its application to the studied grove produced the mid-season Kcb values ranging from 0.40–0.45 and end-season Kcb values ranging from 0.35–0.40. The comparison between the A&P-computed Tc act A&P and TSF field shows RMSE values ranging from 0.27 to 0.43 mm d1, which demonstrates the adequacy of the latter approach for parameterizing water balance models and for irrigation scheduling decision makinginfo:eu-repo/semantics/publishedVersio

Dual crop coefficient approach in vitis vinifera L. cv. Loureiro

Vineyard irrigation management in temperate zones requires knowledge of the crop water requirements, especially in the context of climate change. The main objective of this work was to estimate the crop evapotranspiration (ETc) of Vitis vinifera cv. Loureiro for local conditions, applying the dual crop coefficient approach. The study was carried out in a vineyard during two growing seasons (2019?2020). Three irrigation treatments, full irrigation (FI), deficit irrigation (DI), and rainfed (R), were considered. The ETc was estimated using the SIMDualKc model, which performs the soil water balance with the dual Kc approach. This balance was performed by calculating the basal coefficients for the grapevine (Kcb crop) and the active soil ground cover (Kcb gcover), which represent the transpiration component of ETc and the soil evaporation coefficient (Ke). The model was calibrated and validated by comparing the simulated soil water content (SWC) with the soil water content data measured with frequency domain reflectometry (FDR). A suitable adjustment between the simulated and observed SWC was obtained for the 2019 R strategy when the model was calibrated. As for the vine crop, the best fit was obtained for Kcb full ini = 0.33, Kcb full mid = 0.684, and Kcb full end = 0.54. In this sense, the irrigation schedule must adjust these coefficients to local conditions to achieve economically and environmentally sustainable production.E518-D54F-9490 | Susana Miguel Afonso Mendes MouraN/