Abstract
The soil exchange complex consists of colloidal materials on which ion exchange phenomena occur allowing it to attract, retain, and exchange elements that have opposite electric charges. Since their mineral constituents (clay) and organic components (humus) are mainly of a negative nature retained or exchanged ion are predominantly cations. Historically, failing to monitor parameters like the exchange sodium percentage (ESP) has led to the permanent deterioration of soils which have become completely unproductive, largely reducing the sustainability of the agricultural systems. This study assesses how the sodium exchange capacity in irrigated soils differs from the rainfed ones through a sample survey that was carried out in the 15,031 ha of the Caia Irrigation Perimeter and adjacent areas, located in the municipalities of Elvas and Campo Maior, Portalegre District, Portugal where 14,280 georeferenced samples were collected from the top soil layer (0–20 cm), which were mixed 10 at a time so that each composite sample representing 11.1 ha. Then the samples were analyzed regarding the most relevant parameters for characterizing the soil exchange complex including the concentrations of exchanged bases and Cation Exchange Capacity (CEC). The results were arranged in a georeferenced grid with 1451 entries. Using classical statistical analysis and Geographic Information Systems (GIS) software, it was possible to relate the individual soil samples analyzed with the cultural system practiced (irrigated or rainfed) and the present soil group which permitted us to analyze the influence of the cultural system in the soil exchange complex. The distribution chart of the exchange sodium and CEC were created. The obtained results confirm a general decrease of CEC values and an increase of the exchangeable sodium content of irrigated explored soils when compared to the rainfed ones, putting forward noteworthy ideas not only regarding the necessary changes towards the sustainability of these irrigated agricultural landscapes, but also considering the impact of these productive techniques on different agricultural systems.
Highlights
We currently live in a world where near 1500 million hectares of land are used to produce crops that feed the more than 7200 million people who live in it [1]
FigFuirgeur5e. 5D. iDstirsitbriubtuiotinonmmaappooffeexxcchhaanngge sodiiuummlleevveelslsininththe eCCaiaiaIrrIirgraigtiaotnioPnerPiemreimtere.ter. As it has been concluded by previous studies [31,32], in general, irrigation leads to significant decreases in Cation Exchange Capacity (CEC)
The analysis performed in this study enabled us to put forward some precise data regarding the effect of irrigation in different soil groups, the Cambisols being the group where this decrease is more evident and the Calcisols and Luvisols being the ones where the values of these parameters undergo a minor change along irrigation practice
Summary
We currently live in a world where near 1500 million hectares of land (nearly 12% of the total land area of the world) are used to produce crops that feed the more than 7200 million people who live in it [1]. There is a tendency for an inverse evolution of these two factors and we may recognize the near future challenge in agriculture: to be able to produce more with fewer resources. To address this problem a serious intervention will be required—by governments, stakeholders, agricultural specialists, farmers, etc.—in order to enable the application of socio-economic policies to curb the acceleration, and even create an inversion of population growth while simultaneously implementing other measures as a greater investment in research to improve all the production aspects of a crop while preventing the deterioration from agricultural soils. By thoroughly studying all these parameters and applying these studies in practice can we achieve the goal of feeding a population of 10.000 million people by the year 2050, with fewer resources than those available today, while ensuring that the alarming number of people who daily have a “food intake insufficient to meet the energy requirements of the diet” [1] does not increase
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