M. C. Gonçalves

Multicomponent solute transport in soil lysimeters irrigated with waters of different quality

[1] A variety of analytical and numerical models have been developed during the past several decades to predict water and solute transfer processes between the soil surface and the groundwater table. While many models quantifying solute transport in soils usually consider only one solute and severely simplify various chemical interactions, others such as the geochemical module of HYDRUS-1D consider multiple solutes and their mutual interactions. In this study we use HYDRUS-1D to analyze water flow and solute transport in three soil lysimeters (1.2 m 2 � 1 m) irrigated during the summer months with waters of different quality that were used to evaluate salinization and alkalization hazards. The soil monoliths were constructed in a Eutric Fluvisol in Alentejo, Portugal. The electrical conductivity (EC) of irrigation water varied between 0.4 and 3.2 dS m � 1 , and the sodium adsorption ratio (SAR) varied between 1 and 6 (mmol(c) L � 1 ) 0.5 , while maintaining a ratio of Ca:Mg equal to 1:2. The soil monoliths were subjected to regular rainfall and leaching during the rest of the year. Water contents and fluxes, concentrations of individual ions (Na + ,C a 2+ , and Mg 2+ ), electrical conductivity of

Mineral Leaf Composition of Sweet Sorghum in Relation to Biomass and Sugar Yields under Different Nitrogen and Salinity Conditions

Diagnosing nutrient insufficiencies or toxicities in sorghum through foliar analysis is still unusual and mainly used for grain sorghum. The influences of the combinations of four nitrogen (N) rates with three sodium chloride (NaCl) rates on the leaf N, phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) concentrations of sweet sorghum [Sorghum bicolor (L.) Moench ssp. saccharatum], cropped for ethanol production, and on biomass and sugar yields were evaluated in three consecutive years of an experiment established on a Eutric Fluvisol equipped with a trickle irrigation system (“triple emitter source”). The relationships among leaf nutrient concentrations, dry matter, and sugar yields were also examined. Nitrogen, much more than salinity, affected leaf nutrient concentration, stem dry weight, and sugar yield. Leaf N concentration was the best indicator for predicting sugar production of sweet sorghum.

Development of class pedotransfer functions for integrating water retention properties into Portuguese soil maps

Hydrological modellers have recently been challenged to improve watershed models by better integrating soil information into model applications. Reliable soil hydraulic information is thus necessary for better describing the water balance components at the catchment scale. Frequently, that information does not exist. This study presents a set of class-pedotransfer functions (PTFs) for estimating the water retention properties of Portuguese soils. The class-PTFs were established from a dataset containing 697 soil horizons/layers, by averaging values of total porosity and volumetric water contents at –0.25, –1, –3.2, –6.3, –10, –33, –100, –250, and –1500 kPa matric potentials after grouping data by soil texture class, soil horizon, and bulk density. Fitted retention curves using the van Genuchten model were also obtained for every class-PTF. The root mean square error varied between 0.039 and 0.057 cm3/cm3, with smaller values found when using the 12 texture classes of the International Soil Science Society (ISSS) system rather than the five texture classes of FAO, and when bulk density was also considered. The class-PTFs were then integrated into Portuguese soil maps and its usage was demonstrated by deriving maps of available water capacity to be used for modelling the water balance in a small catchment area with the SWAT model. The model successfully simulated the reservoir inflow when using the derived maps, but the results did not vary much whether using coarser or finer description of the catchment soils. Nonetheless, the class-PTFs contributed to a better soil characterisation than when using coarse-scaled information. The approach followed here was simple, inexpensive, and feasible for modellers with few resources but interested in considering the spatial variability of soil retention properties at large scales and in advancing hydrologic modelling in Portugal.

Effect of Combined Use of Brackish Water and Nitrogen Fertilizer on Biomass and Sugar Yield of Sweet Sorghum

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.

Effect of Electrolyte Concentration on Sodium Adsorption: Application of Competitive Extended Freundlich Isotherms

ABSTRACT Mathematical models are often used to simulate water movement and transport of ions, through the soil profile, as a tool to implement better agricultural practices. The most important input data for such models are the unsaturated soil hydraulic properties, solute transport parameters, and adsorption isotherms, the latter relating the concentration of ions at equilibrium in soil solution the concentration of the ions absorbed by each type of soil. As Na adsorption depends not only on Na concentration in solution, but also on the composition of the electrolyte, mainly [ Ca + Mg], competing to adsorption sites, the Freundlich model to describe monocomponent Na adsorption, as well as a competitive extended Freundlich equation, were applied to study Na adsorption in a Fluvisol, considering the application of three different quality irrigation waters. Equations of the Freundlich type, relating exchangeable Na percentage (ESP) and Na adsorption ratio (SAR), ESP = K*(SAR) m , were also determined. The parameters k, k* and K* for the monocomponent extended Freundlich isotherms and ESP–SAR, respectively, decreased with increasing electrolyte concentration, and increased with depth. The K* parameters presented the smallest variation coefficient. Sodium adsorption increased with increasing SAR. For the same SAR, adsorbed Na was independent of the total electrolyte concentration. Distribution coefficients increased with depth, and, for each depth, decreased with increasing electrolyte concentration in the applied solutions, due to competitive adsorption with Ca + Mg.

Modeling flood dynamics in a temporary river draining to an eutrophic reservoir in southeast Portugal

Abstract Enxoé is a small temporary river with a flushy regime, which flash floods carry significant loads to the reservoir. As a result, the reservoir, which supplies 25,000 inhabitants, exhibits a high trophic state and cyanobacteria blooms since its construction in 1998, with water abstractions requiring extensive treatment. This study aimed to understand the contribution of flash floods to the Enxoé’s reservoir high trophic state using a modeling approach. This was the first time the river was monitored and that a modeling study was carried out. The MOHID-Land model was implemented to assess the water path in the catchment, and was integrated with field data to compute river loads. Results confirmed the importance of flash events. During flash floods, water properties were determined by soil surface and river bottom wash out, and depended mostly on the flush sequence and intensity. Model simulations showed that soil surface permeability reduction was an important factor regulating surface runoff while soil moisture was low. The first flood after the dry period contributed to 2% of the yearly discharge, 3% of yearly N load, and 7% of the yearly P loads. Winter floods contribution differed, producing 10% of both yearly discharge and loads. However, concentration of particulate matter and organic compounds in the first flood were one order of magnitude higher than in winter floods. This was due to river bottom resuspension and erosion of riparian areas, representative dynamics of a flushy regime. During subsequent winter floods, nutrient concentrations tended to remain constant as the watershed surface and respective soils were washed. Further work should link a watershed model to a reservoir model to depict the flood impact in the reservoir, and test management strategies to reduce the reservoir trophic state.