Reference grass evapotranspiration with reduced data sets: parametrization of the FAO Penman-Monteith temperature approach and the Hargeaves-Samani equation using local climatic variables

The computation of the grass reference evapotranspiration with the FAO56 Penman-Monteith equation (PM-ETo) requires data on maximum and minimum air temperatures (Tmax, Tmin), actual vapour pressure (ea), shortwave solar radiation (Rs), and wind speed at 2m height (u2). 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 ETo with the Hargreaves-Samani (HS) equation. For the PMT approach, procedures refer to predicting: (a) the dew point temperature (Tdew) from the minimum or the mean air temperature; (b) shortwave solar radiation (Rs) from the air temperature difference (TD=Tmax-Tmin) combined with a calibrated radiation adjustment coefficient (kRs); and (c) wind speed (u2) using a default value or a regional or local average. The adequateness of computing Tdew from air temperature was reassessed and the preference for using an average u2 has been defined. To ease the estimation of Rs, for the PMT approach and the coefficient of the HS equation, multiple linear regression equations for predicting kRs 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 kRs 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 kRs 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, ETo estimated with PMT and HS (ETo PMT and ETo HS) were compared with PM-ETo computed with full data sets to evaluate the usability of the kRs equations. Adopting the climate-focused kRs equations with ETo PMT, the RMSE averaged 0.59, 0.64, 0.65 and 0.72mm d−1 for humid, sub-humid, semi-arid, and arid and hyper-arid climates, respectively, while the RMSE values relative to ETo HS when using the respective climate-focused kRs equations averaged 0.58, 0.60, 0.60 and 0.69mm d−1 for the same climates. These results are similar to those obtained with the kRs global equation. The accuracy of the PMT approach when using the kRs equations was also evaluated when one, two, or all three Tdew, Rs and u2 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 kRs equations for an efficient parameterization of both the PMT approach and the HS equation is demonstrated with similar performance of PMT and HS procedures for a variety of climates. Because the ETo HS results depend almost linearly on temperature, the PMT approach, using estimates of the weather variables, is able to mitigate those temperature impacts, which trends may be contrary to those of other variables that determine ETo. The clear advantage of the PMT approach is that it allows using the available weather data in combination with estimates of the missing variables, which provides for more accurate ETo computationsinfo:eu-repo/semantics/publishedVersio

Crop water requirements and crop coefficients for jute mallow (Corchorus olitorius L.) using the SIMDualKc model and assessing irrigation strategies for the Syrian Akkar region

Jute mallow (Corchorus olitorius L.) is an annual crop grown for human consumption of its nutritious leaves in many regions of the world. Despite its importance for household food security and farmers’ income, reliable information on the crop’s water requirements is still quite scarce. To overcome this knowledge gap, the irrigation needs of jute mallow grown in the Akkar region in Syria were investigated. The analysis focused on a three-year period (2017–2019) where the SIMDualKc model was calibrated and validated for simulating soil water contents and computing the soil water balance in jute mallow plots irrigated with basin and drip methods. The model was further used to determine the probabilities of the demand for irrigation water in scenarios considering different crop season lengths, irrigation methods, and application depths over a longer period of 23 years (1998–2020). The SIMDualKc model was able to simulate soil water contents measured in the field plots, returning root mean square error values lower than 0.001 m3 m-3 and modeling efficiencies ranging from 0.358 to 0.812. The calibrated basal (non-stressed) crop coefficients (Kcb) were 0.15, 0.95, and 0.95 for the initial (Kcb ini), mid-season (Kcb mid), and end-season (Kcb end) stages, respectively. The crop was harvested twice per season, with the drip treatments presenting the highest water productivity and economic indicators. In contrast, the basin treatment resulted in substantial percolation losses, which affected yields and indicators. Although net irrigation requirements showed a large variation for the extremes of the long-term weather time series, differences between the years representing average water demand and those representing very high water demand were only found for the drip irrigation scenarios. This study contributes to improving irrigation water management of jute mallow in the Syrian Akkar region, and for the sustainability of local production systemsinfo:eu-repo/semantics/publishedVersio

The design and evaluation of travelling gun irrigation systems: enrolador software

Technical Paperinfo:eu-repo/semantics/publishedVersio

Separation and Characterisation of the C

The purpose of this work is to isolate and characterise the light fraction of Safaniya, a conventional nonbiodegraded type II crude oil. This fraction is devoted to perform a kinetic study on the thermal stability of the light aromatic fraction of crude oil. The light cut <250°C, corresponding to the C15- components, was obtained by fractionated distillation. This cut contains saturated and aromatic hydrocarbons. Kinetic studies on the thermal stability of aromatics require to separate the aromatic fraction without any trace of saturated compounds and derive detailed information on its composition. We have therefore developed a method permitting to achieve a clear-cut separation of these two families. Liquid phase chromatography on activated silica gel column was thus optimised for separating a complete and pure aromatic fraction, in large enough amounts for characterisation and all subsequent kinetic studies. Thereafter, Preparative High Performance Liquid Chromatography (PHPLC) of an aliquot was used to separate the aromatic compounds according to aromatic ring number into monoaromatics, indenes, diaromatics and biphenyls. Detailed molecular characterisation of the aromatic sub-fractions thus obtained was achieved by Gas Chromatography coupled to Mass Spectrometry (GC/MS). Then, individual aromatic compounds were quantified by GC-FID. These compounds are benzene, C1-C7 benzenes, naphthalene, C1-C7 naphthalenes, indane, C1-C4 indanes, indene, C1-C7 indenes, C1-C3 tetralins and and sulphur-containing aromatics (methyl- and ethylbenzothiophenes). The detailed knowledge thus derived on the composition of different class and its relative abundance in the total C15- aromatics will allow following its temporal evolution during subsequent pyrolysis experiments

Soil salinization in very high-density olive orchards grown in southern Portugal: Current risks and possible trends

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

Avaliação do balanço de água e de sais no solo em três culturas permanentes do perímetro de rega do Roxo.

O regadio é fundamental para a produção agrícola em Portugal. As previsões de alterações climáticas mostram uma tendência para verões mais quentes e secos, e precipitação com uma maior irregularidade na sua distribuição. O aumento de evapotranspiração associado à rega poderá levar a uma maior concentração de sais no solo e por consequência, a um aumento do risco de salinização e da perda de produção das culturas. Por estas razões, a monitorização e controlo da salinização do solo são fundamentais para a sustentabilidade do regadio. Este trabalho teve como objetivo avaliar o balanço de água e sais no solo de três culturas permanentes (olival, amendoal, clementinas) situadas no perímetro de rega do Roxo, em Aljustrel, nos anos de 2019 e 2020. Foram monitorizados os teores de água e a condutividade elétrica do extrato de saturação do solo a diferentes profundidades. Foi depois utilizado o modelo HYDRUS-1D para simular a dinâmica da água e sais no solo e avaliar a sustentabilidade das práticas agrícolas existentes. Os resultados demonstraram que não há um aumento da salinidade no solo nos três locais monitorizados, embora seja importante melhorar as práticas de rega para maximizar a eficiência do uso da água aplicada