Abstract
In semi-arid and arid areas, soil salinity has adverse effects both on the environment and agricultural production. The main causes of this salinization come from natural or anthropogenic processes, which is certainly an environmental problem that affects more than 20% of the world's land. This study was made in order to map the spatial distribution of soil salinity of the irrigated perimeter of El Ghrous in southeastern Algeria. These maps were performed based on data collected from 190 soil samples from 0 to 15 cm deep. We used ordinary kriging (OK) to analyze the spatial variability of soil salinity, while indicator kriging (IK) was used to analyze salinity versus threshold values. The salinity map predicted by the electrical conductivity (EC) values using the ordinary kriging (OK) method showed the different classes of salinity according to Durand's classification with moderately saline 3rd order dominance, while the unsalted soil (EC &lt; 0.6 dS m<sup>-1</sup>) represents a very low percentage (1.5%). The indicator kriging (IK) was carried out by four thresholds which correspond to the salinity class limits: EC &gt; 0.6, EC &gt; 1, EC &gt; 2, EC &gt; 3, and EC &gt; 4 dS m<sup>-1</sup>, for developing probability maps to determine risk areas. This study has shown the spatial trend of soil salinity by geolocation of different classes, and to carry out risk maps using geostatistical techniques.
Highlights
IntroductionSoil salinization is one of the forms of land degradation that causes difficulties for vegetation growth by influencing soil quality over time, leading to unsustainable agriculture and declining biodiversity and reducing water quality and agricultural production, resulting in sterile land due to excess salts dissolved in the surface soil of arid and semi-arid regions (Fan et al 2011; Bui 2013; Aragüés et al 2014; Cassel et al 2015).According to Gorji et al (2015) the practice of ancient irrigation techniques as well as unconscious irrigation with salt-rich waters, clearing and the use of fertilizers rich in nitrogen and potassium salts are among the factors causing soil salinity, in addition to other natural factors such as parent material, soil structure, groundwater levels close to the surface, degradation of saline source rock and seawater
Despite the development projects and efforts that have been made as part of the State's agricultural land concession, the irrigated area of El Ghrous requires the following perspectives that we considered useful: application of leaching rates to ensure that salts accumulate deeper in the soil, installation of drainage networks to keep the aquifer level below the critical salinization level, permanent monitoring and maintenance drains for the evacuation of contaminated water, crop selection based on salinity tolerance, and improvement of irrigation management taking into account the network and the techniques and frequencies that are used
The main objective of this study is to predict soil salinity at the irrigated perimeter of El Ghrous, for which we opted for two types of kriging: ordinary to map spatial variability and indicator kriging to map the probability of exceeding critical salinity thresholds for crop yield and soil degradation
Summary
Soil salinization is one of the forms of land degradation that causes difficulties for vegetation growth by influencing soil quality over time, leading to unsustainable agriculture and declining biodiversity and reducing water quality and agricultural production, resulting in sterile land due to excess salts dissolved in the surface soil of arid and semi-arid regions (Fan et al 2011; Bui 2013; Aragüés et al 2014; Cassel et al 2015).According to Gorji et al (2015) the practice of ancient irrigation techniques as well as unconscious irrigation with salt-rich waters, clearing and the use of fertilizers rich in nitrogen and potassium salts are among the factors causing soil salinity, in addition to other natural factors such as parent material, soil structure, groundwater levels close to the surface, degradation of saline source rock and seawater. Soil salinization is one of the forms of land degradation that causes difficulties for vegetation growth by influencing soil quality over time, leading to unsustainable agriculture and declining biodiversity and reducing water quality and agricultural production, resulting in sterile land due to excess salts dissolved in the surface soil of arid and semi-arid regions (Fan et al 2011; Bui 2013; Aragüés et al 2014; Cassel et al 2015). Regular monitoring of land degradation processes, especially in arid and semi-arid zones, provides a precise estimate of the spatial variation in soil salinization on large areas and ensures effective soil and water management and the sustainability of agricultural land use (Afrasinei et al 2017; Wang et al 2018). That endangers the national economy of some countries, such as Argentina, Egypt, India, Iraq, Pakistan, Syria and Iran (Rhoades 1990)
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