Fernando P. Pires’s research while affiliated with Instituto Nacional de Investigação Agrária e Veterinária (INIAV) and other places

The mitigation of soil salinization and/or sodicization phenomena are considered one of the main challenges of irrigated agriculture. In Portugal, Lezíria Grande of Vila Franca de Xira is a region with increased salinization and sodicization risks due to the influence of tidal movement on groundwater. This study aimed to evaluate soil water and salt dynamics in an irrigated Fluvisol with a crop rotation of maize and annual ryegrass and to predict irrigation-induced risks of soil salinization. We first calibrated the Hydrus-1D model for predicting soil water flow and solute transport with observed field data (from June 2017 to October 2018). Hydrus-1D successfully simulated soil water content (RMSE= 0.019 m 3 m-3 and R 2 = 0.94), the total dissolved solids (TDS) in the soil (RMSE= 0.212 g L-1 and R 2 = 0.77) and the reduction in water uptake by roots due to osmotic stress. Afterward we evaluate future risks of soil salinization performing a scenario analysis considering irrigation with different water qualities (with an electrical conductivity of the irrigation water, ECw, of 1.5, 3 and 5 dS m-1). We observed that when the ECw increases to 5 dS m-1 , the average solute concentration in the root zone rises to levels above the threshold tolerance of maize. Hydrus-1D successfully simulated soil water content and the total dissolved solids and is a very useful tool in planning and managing irrigation and in predicting soil salinity risks. R E S U M O O controlo e a mitigação dos fenómenos de salinização e/ou sodização dos solos são considerados um dos principais desafios da agricultura de regadio. Em Portugal, a Lezíria Grande de Vila Franca de Xira é uma região com riscos de salinização e sodização do solo acrescidos pela sua localização costeira e com influência das marés. Neste estudo, pretendeu-se avaliar a dinâmica da água e dos sais num Fluvissolo com rotação de milho e azevém anual e avaliar futuros riscos de salinização do solo induzidos pela rega. Este estudo iniciou-se com a calibração do modelo Hydrus-1D para prever o teor de água no solo e o transporte de solutos com medições de campo (de Junho 2017 a Outubro 2018). O Hydrus-1D simulou com sucesso o teor de água no solo (RMSE= 0.019 m 3 m-3 e R 2 = 0.94), o teor de sólidos dissolvidos (TDS) no solo (RMSE= 0.212 g L-1 e R 2 = 0.77) e a redução na absorção de água pelas raízes devido ao stress osmótico. Em seguida, o modelo foi usado na previsão de riscos de salinização do solo com uma análise de cenários considerando diferentes qualidades da água de rega (ECw de 1.5, 3 e 5 dS m-1). Observou-se que com a subida da ECw para 5 dS m-1 , a concentração média de solutos no perfil de solo explorado pelas raízes aumenta para níveis superiores aos tolerados pela cultura de milho. O Hydrus-1D simulou o teor de água no solo e o teor de sólidos dissolvidos no solo com sucesso e é uma ferramenta muito útil no planeamento e gestão da rega e na previsão de riscos de salinidade do solo.

The mitigation of soil salinization and/or sodicization phenomena are considered one of the main challenges of irrigated agriculture. In Portugal, Lezíria Grande of Vila Franca de Xira is a region with increased salinization and sodicization risks due to the influence of tidal movement on groundwater. This study aimed to evaluate soil water and salt dynamics in an irrigated Fluvisol with a crop rotation of maize and annual ryegrass and to predict irrigation-induced risks of soil salinization. We first calibrated the Hydrus-1D model for predicting soil water flow and solute transport with observed field data (from June 2017 to October 2018). Hydrus-1D successfully simulated soil water content (RMSE= 0.019 m3m-3 and R2= 0.94), the total dissolved solids (TDS) in the soil (RMSE= 0.212 g L-1 and R2= 0.77) and the reduction in water uptake by roots due to osmotic stress. Afterward we evaluate future risks of soil salinization performing a scenario analysis considering irrigation with different water qualities (with an electrical conductivity of the irrigation water, ECw, of 1.5, 3 and 5 dS m-1). We observed that when the ECw increases to 5 dS m-1, the average solute concentration in the root zone rises to levels above the threshold tolerance of maize. Hydrus-1D successfully simulated soil water content and the total dissolved solids and is a very useful tool in planning and managing irrigation and in predicting soil salinity risks.

The Enxoé reservoir in southern Portugal has been exhibiting the highest trophic state in the country since its early years of operation. The problem has attracted water managers’ and researchers’ attention as the reservoir is the water supply for two municipalities. Extensive research was thus conducted over the last few years, including field monitoring and modelling at the plot, catchment, and reservoir scales. This study now frames all partial findings within the Driver-Pressure-State-Impact-Response (DPSIR) framework to better understand the eutrophication process in the Enxoé reservoir. Agriculture and grazing were found to have a reduced role in the eutrophication of the reservoir, with annual sediment and nutrient loads being comparably smaller or similar to those reported for other Mediterranean catchments. Flash floods were the main mechanism for transporting particle elements to the reservoir, being in some cases able to carry up three times the average annual load. However, the main eutrophication mechanisms in the reservoir were P release from deposited sediment under anoxic conditions and the process of internal recycling of organic matter and nutrients. Reducing the P load from the catchment and deposited sediment could lead to a mesotrophic state level in the reservoir. However, this level would only be sustainable by limiting the P internal load ability to reach the photic zone.

Nowadays there is an increasing effort for raising global awareness for the importance of soils to ensure food security, to improve agricultural and environmental planning and monitoring, and to establish effective and sustainable land management policies to counteract soil degradation. This study presents the INFOSOLO legacy database as the first effort to develop a soil information system in Portugal, suitable to compile soil data produced in the country, and to support stakeholders and land managers in decision-making. The database currently includes soil data from a set of 9934 horizons/layers studied in 3461 soil profiles across the country between 1966 and 2014. Data was extracted from scattered soil surveys, research projects, and academic studies carried out by public Portuguese and other European institutions, with a series of validation tests and harmonization procedures being implemented in order to access and improve the quality of the data. The importance of the INFOSOLO legacy dataset was discussed and exemplified with the analysis of the spatial and temporal distribution of selected soil properties, namely the organic carbon content, pH, and cation exchange capacity. For these properties, 1 km grid maps were also developed for the topsoil horizons/layers in Portugal using different spatial modelling approaches. To highlight the importance of using INFOSOLO for soil characterization, the EU wide soil database LUCAS was used to compare both datasets in terms of data distributions, spatial continuity and accuracy of modelling outputs. The comparison also included the digital soil maps provided by the SoilGrids product for Portugal. The comparison results highlighted specific areas in the country for which INFOSOLO is capable to deliver accurate but also more reliable predictions when compared with the LUCAS and SoilGrids results. Thus, INFOSOLO provides the basis for improving soil information in the country and for raising national awareness of the importance of soil resources to the country's development.

The temporal variability of particulate (POC) and dissolved (DOC) organic carbon concentrations was analyzed in the Enxoé temporary river, southern Portugal, between September, 2010 and August, 2013. The overall aim was to study the variability of those elements during storm events, and determine their origin and the main transfer mechanisms to the river. Twenty-one flood events were observed. An empirical model was used to describe changes in solute concentrations, and the magnitude and rotational patterns of the hysteretic loops during flood events. POC and DOC concentrations varied between 0.49-88.93 and 0.25-25.75 mg L-1, respectively. POC and DOC annual yields varied between 0.06-2.15 and 0.03-1.47 t km-2, respectively. Flood events had greater effect in POC than in DOC variability. POC had mostly a terrestrial origin, with exports being related to soil erosion and runoff. POC revealed a flushing behavior during the entire monitored period, and clockwise or anticlockwise trajectory loops whenever the predominant origin of the exports was in river bed deposits or arable lands, respectively. DOC had also a terrestrial origin, but it revealed a contrasting dilution behavior and, in general, anticlockwise hysteresis loops. DOC showed a delay in the arrival of solutes to the river, consistent with mass flow through subsurface flow. DOC exports were thus associated with soil weathering and crop mineralization. This work highlights the main processes involved in POC and DOC loads in a temporary river during flood events, with a precise quantification of those elements.

Soil salinization and non-point source pollution are among the most important and widespread environmental problems in European Mediterranean regions. Sweet sorghum (Sorghum bicolor (L.) Moench var. saccharatum) is a moderate to high salinity tolerant crop with low water and nutrient needs, seen as an alternative to grow in the water scarce regions. A three-year multifactorial study was conducted in southern Portugal to evaluate the combined effects of saline water and nitrogen application on the dry biomass (total, stems, and leaves), sugar content (total reducing sugars and sucrose contents), and sugar yield (here defined as the product of total reducing sugars and stems dry biomass) functions of sweet sorghum. Sorghum dry biomass and sugar yield showed diminishing returns for each incremental change of nitrogen. The use of saline irrigation waters also led to yield reduction. Exception was sucrose content which increased with increasing levels of sodium in the soil. Nitrogen need decreased as the amount of sodium applied increased. Stem dry biomass, sucrose content, and sugar yield progressively increased with progress in the experiment. The effect could be attributed to the increase of the amount of irrigation applied throughout the years, thus increasing the leaching fraction which promoted salt leaching from the root zone, reduced the salinity stress, increased plant transpiration, nitrogen uptake and biomass yield.

We evaluated the influence of the combinations of four N levels with three NaCl levels, applied through irrigation, on leaf N, P, K, Ca, Mg, and Na concentrations of sweet sorghum (Sorghum bicolor ssp. saccharatum), in two consecutive years of an experiment established on a Eutric Fluvisol in Alvalade-Sado region, equipped with a drip irrigation system ("Triple Linear Source"). The relationships between leaf nutrient concentrations and dry matter production (stems, leaves, and aerial biomass), and between N and NaCl levels and the leaf nutrient concentrations were also searched. It was nitrogen availability in soil that, more than salinity, affected nutrient uptake, with reflexes on the leaf concentrations and the yields. Leaf N concentration was the best indicator for predicting the stems production of sweet sorghum.

Soil texture influences significantly soil hydraulic properties, which due to soil heterogeneity normally present large spatial variability. The variability of soil retention θ(h), and hydraulic conductivity K(h) curves, in 11 of the 12 texture classes of the diagram of Gomes e Silva (1962) was studied. For each textural class, average, maximum, minimum, and the standard deviation values for the Mualem van Genuchten parameters are presented based on 558 θ(h) and 245 K(h) curves determined in undisturbed soil samples which are included in the PROPSOLO database of Estação Agronómica Nacional. An average function describing θ(h) and K(h) in each textural class is also presented.