Abstract
High salt concentration in soil is a major abiotic stress, which adversely influences the growth, overall development, and productivity of crops. More than 20% of the land of the world used for crop production is adversely affected by high salt concentration. The problem of salt stress becomes a major concern when previously fertile, productive agricultural lands are salinized more profoundly as a result of anthropogenic activities along with natural causes. Therefore, this review is focused on various aspects of salt-affected soils (SAS), their effects on plants, and different approaches for reclamation of SAS to enhance the potentiality for crop production. Salt-affected soils are categorized into saline, saline-sodic, and sodic soils based on the amount of total soluble salts as expressed by electrical conductivity (EC), sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and soil pH. The inhibition of plant growth in saline soils is mainly induced by osmotic stress; reduced uptake of essential macro- and micronutrients, including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu); and specific toxicities of sodium (Na) and chloride (Cl). Sodic soils adversely affect the plant through high soil pH and poor physical condition resulting from an excessive amount of exchangeable Na. Different plants respond to salt stress in different extents. Salt-affected soils must be reclaimed to restore their productivity for increasing food production. The approaches for the management of SAS include leaching, incorporation of different organic and inorganic amendments, mulching, and development of salt-tolerant crops. The suitability of approaches depends on several considerations such as cost of reclamation, the time required, the extent of the salt stress, soil properties, availability of technology, and other environmental factors. Among different strategies, the incorporation of organic amendments is beneficial, cost-effective, environment friendly, and sustainable for amelioration of salt stress and enhancement of crop production due to the extensive roles of organic amendments in improving the soil’s physical (structural stability, porosity, and permeability), chemical [pH, EC, ESP, organic matter, cation exchange capacity (CEC), and Na leaching], and biological and/or biochemical (microbial abundance, microbial activity, biomass carbon, and enzymatic activities) properties.
Highlights
The term stress in plants is defined as the environmental constraint that leads to the inhibition of morphological, physiological, and biochemical functioning of plants adversely affecting their growth and development [1–4]
Salt-affected soils are categorized into saline, sodic, and saline-sodic groups based on the amount of total soluble salts (TSS), sodium adsorption ratio (SAR; the ratio of Na+ to Ca2+ and Mg2+ on the exchange sites of soil), exchangeable sodium percentage [ESP; the relative amount of the Na+ ion expressed as a percentage (%) to the cation exchange capacity (CEC) or the sum of exchangeable bases], and soil pH
Botella et al [67] reported that the increased concentration of NaCl in the root medium decreased the net uptake of N more profoundly in NO3− compared to the NH4+ form when their compounds were incorporated as the source of N, which was assumed to be a reason for the greater affinity for NH4+ compared to NO3− under the saline environment
Summary
The term stress in plants is defined as the environmental constraint that leads to the inhibition of morphological, physiological, and biochemical functioning of plants adversely affecting their growth and development [1–4]. Similar to K, the uptake and transport of Ca and Mg can be adversely affected by the high concentrations of Na commonly found in saline soils, resulting in lower Ca:Na and Mg:Na ratios in plants [24]. The approaches for the management of SAS include removal of salts from the root zone through leaching, incorporation of organic and inorganic amendments, mulching, maintaining groundwater table, and cultivating crops tolerant to salt stress [26, 27]. In salt-affected areas, different methods are applied to remove excess soluble salts from the root zone of plants to improve crop growth and production. Different approaches that can be practiced for the amelioration of SAS have been discussed with the aim to improve soil health and boost up crop production in sustainable ways for ensuring food security worldwide
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