Improving surface irrigation systems for cotton in Ras-El-Ain district, Northeast Syria, needs finding alternative solutions that provide for both water saving and farm economic benefits in a context of small and family farms. Multicriteria analysis was used to evaluate and rank a set of furrow and border irrigation alternatives, with and without precise land leveling, that were created with the decision support system SADREG. This approach allowed to consider various criteria, mainly water saving and farm economics. Results show that both graded furrow and border alternatives are acceptable, with a slight advantage for graded furrows. Alternatives without land leveling have shown to be more appropriate when focusing farm economic results, while alternatives including land leveling were selected when priorities were assigned to water saving. These results relate with higher costs of alternatives that consider land leveling. Equipment for appropriate control of inflow rates was considered for all cases. The improved alternatives may lead to savings of 20-28% of irrigation water and increasing the irrigation water productivity from present 0.31 to 0.44 kg m −3. When the same alternatives were ranked for a 20% deficit irrigation their rankings changed, with reduced ranks of alternatives requiring land leveling. This is due to the fact that yields and yield values are reduced with deficit irrigation, thus making it less favorable to select alternatives that imply higher costs. The study shows that adopting more advanced but more costly irrigation technologies aimed at water saving requires appropriate economic incentives, training of farmers and an institutional framework able to support the sustainable use of water in irrigation.

Decision support systems Deficit irrigation Model MIRRIG Model SADREG Northeast Syria This study explores the use of drip and surface irrigation decision support systems to select among furrow, border and drip irrigation systems for cotton, considering water saving and economic priorities. Data refers to farm field observations in Northeast of Syria. Simulation of drip irrigation was performed with MIRRIG model for various alternatives: double and single row per lateral, emitter spacing of 0.5 and 0.7 m, six alternative pipe layouts and five self-compensating and non-compensating emitters. Furrow and border irrigation alternatives were designed and ranked with the SADREG model, considering lasered and nonlasered land levelling, field lengths of 50e200 m and various inflow discharges. A multicriteria analysis approach was used to analyse and compare the alternatives based upon economic and water saving criteria. Results for surface irrigation indicate a slight advantagefor long non-lasered graded furrows; non-lasered alternatives were selected due to economic considerations. For drip irrigation, the best ranking is for systems having lower costs, mainly with double rows per lateral and larger emitter spacing. Comparing surface and drip irrigation systems, despite low cost, drip alternatives may lead to 28e35% water saving relative to improved graded furrows, and increase water productivity from 0.43 kg m À3 to 0.61 kg m À3 , surface irrigation provides higher farm returns. Drip irrigation is selected only when high priority is assigned to water saving. Deficit irrigation does not change this pattern of results. Apparently, adopting drip irrigation requires appropriate economic incentives to farmers, changes in the structure of production costs and increased value of production. b i o s y s t e m s e n g i n e e r i n g 1 2 2 ( 2 0 1 4 ) 7 4 e9 0 http://dx.

The computation of the grass reference evapotranspiration with the FAO56 Penman-Monteith equation (PM-ET o ) requires data on maximum and minimum air temperatures (T max , T min ), actual vapour pressure (e a ), shortwave solar radiation (R s ), and wind speed at 2 m height (u 2 ). Nonetheless, related datasets are often not available, are incomplete, or have uncertain quality. To overcome these limitations, several alternatives were considered in FAO56, while many other procedures were tested and proposed in very numerous papers. The present study reviews the computational procedures relative to predicting the missing variables from temperature, i.e., the PM temperature approach (PMT), and estimating ET o with the Hargreaves-Samani (HS) equation. For the PMT approach, procedures refer to predicting: (a) the dew point temperature (T dew ) from the minimum or the mean air temperature; (b) shortwave solar radiation (R s ) from the air temperature difference (TD = T max -T min ) combined with a calibrated radiation adjustment coefficient (k Rs ); and (c) wind speed (u 2 ) using a default value or a regional or local average. The adequateness of computing T dew from air temperature was reassessed and the preference for using an average u 2 has been defined. To ease the estimation of R s, for the PMT approach and the coefficient of the HS equation, multiple linear regression equations for predicting k Rs were developed using local averages of the temperature difference (TD), relative humidity (RH) and wind speed as independent variables. All variables were obtained from the Mediterranean set of CLIMWAT climatic data. Two types of k Rs equations were developed: climate-focused equations specific to four climate types -humid, sub-humid, semi-arid, and hyper-arid and arid -, and a global one, applicable to any type of climate. The usability of the k Rs equations for the PMT and HS methods was assessed with independent data sets from Bolivia, Inner Mongolia, Iran, Portugal and Spain, covering a variety of climates, from hyper-arid to humid. With this purpose, ET o estimated with PMT and HS (ET o PMT and ET o HS ) were compared with PM-ET o computed with full data sets to evaluate the usability of the k Rs equations. Adopting the climate-focused k Rs equations with ET o PMT , the RMSE averaged 0.59, 0.64, 0.65 and 0.72 mm d −1 for humid, sub-humid, semi-arid, and arid and hyper-arid climates, respectively, while the RMSE values relative to ET o HS when using the respective climate-focused k Rs equations averaged 0.58, 0.60, 0.60 and 0.69 mm d −1 for the same climates. These results are similar to those obtained with the k Rs global equation. The accuracy of the PMT approach when using the k Rs equations was also evaluated when one, two, or all three T dew , R s and u 2 variables are missing and the resulting goodness-of-fit indicators demonstrated the advantage of the combined use of observed and estimated weather variables. The usability of the k Rs equations for an efficient parameterization of both the PMT approach and ...

No abstract

No abstract

Deficit irrigation practices carried out in very high-density olive orchards grown in the Alentejo region of southern Portugal can bring important economic benefits in terms of water savings, yields, and oils. They can also result in serious salinization/sodification problems without proper management of soil and water resources. The main objective of this study was to evaluate the long-term (30 years) impact of those irrigation practices on local soil resources using a multicomponent transport modeling approach embedded in the HYDRUS-1D model. Soil salinization and sodification risks were quantified for 160 soil profiles by considering eight different scenarios: current monitored irrigation practices (S1), using waters of variable quality (S2-S6), planting maize as an alternative crop (S7), and using climate change projections for the region (S8). Despite the large observed variability, simulations that considered current irrigation practices (S1) produced average values of the electrical conductivity of the soil solution (EC sw) at the end of the leaching seasons always below the threshold limit for crops moderately tolerant to soil salinity. In this scenario, the average values of the sodium adsorption ratio (SAR) were also kept within the same magnitude of those determined at the beginning of the simulation period (initial conditions). Irrigations with worse quality waters (S2-S6) led to higher EC sw and SAR values. Although annual rainfall amounts influenced the salinity build-up, the SAR evolution depended mainly on water quality. In maize soil profiles (S7), the simulated EC sw and SAR values were lower than in olive soil profiles, with irrigation practices contributing to salt removal during the seasons. Conversely, the climate change scenario (S8) resulted in slightly higher EC sw and SAR values than those simulated for current conditions, indicating a potentially greater risk of soil degradation in the near future. Although current irrigation practices seem to present relatively low soil salinization/sodification risks, the variability of results and the uncertainty associated with model predictions indicate that close monitoring to prevent further degradation of soil and water resources in the region should be recommended.

The southern Iberian Peninsula is characterized by evergreen oak woodlands (locally known as montado), which constitute an important savanna-type agro-silvo-pastoral ecosystem. This ecosystem is facing a progressive decline for several reasons, with the foremost being overgrazing. Better management tools are necessary to accurately quantify the systems' carrying capacity and the sustainable stocking rates that prevent land degradation. The purpose of this study was to determine whether the MOHID-Land model could adequately simulate soil water dynamics and pasture growth in the montado ecosystem. The study area was located in the Alentejo region of southern Portugal. The model successfully simulated soil water contents and aboveground biomass during the 2010-2011 and 2011-2012 growing seasons, producing acceptable errors of the estimates (0.015 ≤ RMSE ≤ 0.026 cm 3 cm −3 ; 279 ≤ RMSE ≤ 1286.5 kg ha −1), and relatively high modeling efficiencies (0.481 ≤ EF ≤ 0.882). The model was further used to simulate the same variables for a longer period (1979/2009 seasons), to account for the effect of climate variability on model estimates. Water balance and dry biomass estimates were found to be significantly different between rainfed and irrigated pastures, as well as between the ten driest and ten wettest seasons, with the model responding well to climate variability. The results showed the potential of using the MOHID-Land model for improving pasture management in the montado ecosystem.

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 (2007−2011) and the other with the same trees but now 18−20 years old, irrigated with different schedules (2015−2019). 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 m−3 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 0.54−0.55 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 systems.