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Soil Salinity Type Effects on the Relationship Betweenthe Electrical sustainability Article Soil Salinity Type Effects on the Relationship between the Electrical Conductivity and Salt Content for 1:5 Soil-to-Water Extract Amin I. Ismayilov 1, Amrakh I. Mamedov 2,* , Haruyuki Fujimaki 2 , Atsushi Tsunekawa 2 and Guy J. Levy 3 1 Institute of Soil Science and Agrichemistry, Azerbaijan National Academy of Sciences (ANAS), Baku AZ1073, Azerbaijan; [email protected] 2 Arid Land Research Center, Tottori University, Tottori 680-0001, Japan; [email protected] (H.F.); [email protected] (A.T.) 3 Institute of Soil, Water and Environmental Sciences, ARO, Rishon LeZion 7505101, Israel; [email protected] * Correspondence: [email protected] Abstract: Soil salinity severely affects soil ecosystem quality and crop production in semi-arid and arid regions. A vast quantity of data on soil salinity has been collected by research organizations of the Commonwealth of Independent States (CIS, formerly USSR) and many other countries over the last 70 years, but using them in the current international network (irrigation and reclamation strategy) is complicated. This is because in the CIS countries salinity was expressed by total soluble salts as a percentage on a dry-weight basis (total soluble salts, TSS, %) and eight salinity types − 2− − + (chemistry) determined by the ratios of the anions and cations (Cl , SO4 , HCO3 , and Na , Ca2+, Mg2+) in diluted soil water extract (soil/water = 1:5) without assessing electrical conductivity (EC). Measuring the EC (1:5) is more convenient, yet EC is not only affected by the concentration Citation: Ismayilov, A.I.; Mamedov, but also characteristics of the ions and the salinity chemistry. The objective of this study was to A.I.; Fujimaki, H.; Tsunekawa, A.; examine the relationship between EC and TSS of soils in a diluted extract (1:5) for eight classic salinity Levy, G.J. Soil Salinity Type Effects on the Relationship between the types. We analyzed extracts (1:5) of 1100 samples of a clayey soil (0–20 cm) collected from cultivated + 2+ 2+ − − Electrical Conductivity and Salt semi-arid and arid regions for EC, TSS, soluble cations (Na , Ca , Mg ), and anions (HCO3 , Cl , 2− 2 Content for 1:5 Soil-to-Water Extract. SO4 ). Results revealed that (i) the variation in the proportional relationships (R ≥ 0.91–0.98) − Sustainability 2021, 13, 3395. https:// between EC (0.12–5.6 dS m 1) and TSS (0.05–2.5%) could be related to salinity type, and (ii) the doi.org/10.3390/su13063395 proportionality coefficient of the relationships (2.2 2–3.16) decreased in the following order of salinity type: SO4 < Cl(SO4)–HCO3 < Cl(HCO3)–SO4 < SO4 (HCO3)–Cl < Cl. The findings suggest that once Academic Editor: Adriano Sofo the salinity type of the soil is established, EC (1:5) values can be safely used for the evaluation of the soil salinity degree in the irrigated land in the context of sustainable soil and crop management. Received: 22 February 2021 Accepted: 16 March 2021 Keywords: total dissolved salts; salinity chemistry; irrigation; dryland; salinity stress Published: 19 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- iations. Cultivated lands, particularly in semi-arid and arid regions or drylands with scarce water resources, spread over more than 100 countries and ~1 billion ha (e.g., Argentina, Australia, China, India, USA) including the Commonwealth of Independent States (CIS, for- merly USSR) are seriously affected by soil salinization and sodicity [1]. This environmental problem involves the ground water–soil–water–plant–atmosphere continuum associated Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. with (i) water potential in the growth medium, which causes decreased transpiration and This article is an open access article net photosynthetic rates (the osmotic effect, salinity degree), reduced capacity of plants − + distributed under the terms and to transform energy to biomass, and accumulation of specific toxic ions (Cl , Na ) to conditions of the Creative Commons levels exceeding the tolerance limits of plants (salinity stress, specific ion effect); (ii) ionic Attribution (CC BY) license (https:// disequilibrium and imbalance of nutrients in the plant, thus harming seed germination, creativecommons.org/licenses/by/ plant stomatal conductance, density and growth, and biomass partitioning between shoots 4.0/). and roots; and (iii) deterioration of soil structure (soil disaggregation and clay dispersion) Sustainability 2021, 13, 3395. https://doi.org/10.3390/su13063395 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, x FOR PEER REVIEW 2 of 11 ionic disequilibrium and imbalance of nutrients in the plant, thus harming seed germina- tion, plant stomatal conductance, density and growth, and biomass partitioning between shoots and roots; and (iii) deterioration of soil structure (soil disaggregation and clay dis- Sustainability 2021persion), 13, 3395 and hydraulic characteristics (solution and air flow) due to high content of ex- 2 of 11 changeable Na+, Mg2+, or K+ when soil electrolyte concentration is below a ”threshold” level [2‒5]. Plant toleranceand hydraulicto salinity characteristics varies with species (solution and and varieties air flow) and due biotic to high and content abiotic of exchangeable fac- + 2+ + tors, yet the growthNa , Mgof most, or Kagriculturalwhen soil electrolyteplants is negatively concentration affected is below by a ”threshold”salinity, which level [2–5]. critically influences soilPlant biological tolerance activities. to salinity The varies remediation with species of andsalt-affected varieties andsoils, biotic partic- and abiotic factors, yet the growth of most agricultural plants is negatively affected by salinity, which ularly secondary salinization, is expensive and difficult. Thus, plant response to soil sa- critically influences soil biological activities. The remediation of salt-affected soils, par- linity (both concentrationticularly secondary and composition salinization, of th ise expensive ions, i.e., andosmotic difficult. stress Thus, and plant specific response ion to soil effects) and irrigationsalinity management (both concentration should and ta compositionke the specific of the circumstances ions, i.e., osmotic into stress account and specific (e.g., leaching fraction,ion effects) salinity and irrigation stress, selection management of shouldcultivars take tolerant the specific to a circumstances certain salinity into account level, deterioration(e.g., of leaching soil physical fraction, quality, salinity role stress, of selectionsoil biota), of cultivarsand the tolerantinterrelationships to a certain salinity that exist amonglevel, soil properties, deterioration salt of soilcomposition, physical quality, and plant role ofspecies soil biota), [2‒6]. and the interrelationships Assessing soilthat salinity exist among is a soilcritical properties, task for salt the composition, Kur‒Araz andbasin plant (600,000 species ha) [2– 6of]. Azer- baijan, which is locatedAssessing in the soil shoreline salinity is area a critical (situated task for below the Kur–Araz sea level basin up (600,000 to 30 ha)m with of Azerbaijan, which is located in the shoreline area (situated below sea level up to 30 m with <300–400 mm <300‒400 mm annual precipitation) and has wide drainage networks. Currently, 60% of annual precipitation) and has wide drainage networks. Currently, 60% of the cultivated and the cultivated andirrigated irrigated land land of the of basin the basin has clayey has clayey soil in thesoil root in the zone root and zone is characterized and is char- by various acterized by variousdegrees degrees and types and types of salinity of salinity (Figure (Figure1)[ 7–9]. 1) The [7‒9]. problem The problem of salinity of insalinity the Kur–Araz in the Kur‒Arazbasin basin of of Azerbaijan, Azerbaijan, as wellas well as in as many in many semi-arid semi-arid and arid and regions arid regions or drylands or of the drylands of the world, isis expected expected to to increase increa withse with the ongoingthe ongoing climate climate change change and shortage and short- in fresh water. age in fresh water.Thus, Thus, frequent frequent monitoring monitoring of salinity of salinity level is level important is important for water for resources water re- allocation sources allocationand and sustainable sustainable management management of salt-affected of salt-affected soils, whichsoils, maywhich have may significant have sig- economic nificant economicramifications ramifications if ill-managed if ill-managed [10]. [10]. Figure 1.FigureSoil salinity 1. Soil map salinity of Kur-Araz map of basin Kur-Araz of Azerbaijan basin of (from Azerbaijan [9]). Salinity (from degree [9]). is Salinity given by degree total soluble is given salts by (TSS, %). 3 Salinitytotal area(10 solubleha): non-saline:salts (TSS, 495.4;%). Salinity slightly area saline: (10 381.8;3 ha):saline: non-saline: 414.6; strongly495.4; slig saline:htly 448.9;saline: extremely 381.8; saline: saline: 174.4. 414.6; strongly saline: 448.9; extremely saline: 174.4. Sustainability of the agroecosystem in salt-affected lands could be preserved by study- ing salinity related soil processes (e.g., the interactions between root–zone environment Sustainabilityand of plant the agroecosystem response to elevated in salt-a osmoticffected pressure, lands could soil–plant–salinity be preserved interaction) by stud- and in- ying salinity relatedtegrating soil processes
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