The usage of inadequately processed industrial waste water (WW) can lead to strong soil alkalinity and soil salinization of agricultural fields with negative consequences on soil properties and biota. Gypsum as a soil amendment to saline-sodic soils is widely used in agricultural fields to improve their soil physical, chemical and hence biological properties. This study aimed at analysing the effects of intensive WW irrigation on the structure and composition of soil-dwelling arthropods on spinach fields (Spinacia oleracea L.) in a West African urban vegetable production system. We used gypsum as a soil amendment with the potential to alleviate soil chemical stress resulting in a potentially positive impact on soil arthropods. A total of 32 plots were established that showed a gradient in soil pH ranging from slight to strong soil alkalinity and that were irrigated with WW (n = 12) or clean water (CW; n = 20), including eight plots into which gypsum was incorporated. Our study revealed a high tolerance of soil-dwelling arthropods for alkaline soils, but spinach fields with increased soil electrical conductivity (EC) showed a reduced abundance of Hymenoptera, Diptera and Auchenorrhyncha. Arthropod abundance was positively related to a dense spinach cover that in turn was not affected by WW irrigation or soil properties. Gypsum application reduced soil pH but increased soil EC. WW irrigation and related soil pH affected arthropod composition in the investigated spinach fields which may lead to negative effects on agronomical important arthropod groups such as pollinators and predators.

Saline-sodic soil is considered the most important low-yield soil in arid and semi-arid regions. Flue gas desulfurization (FGD) steel slag is a kind of by-product from wet FGD process, in which steel slag powder replaces lime as sorbent of SO₂ emitted from coal-fired power plants. It could potentially be used to ameliorate saline-sodic soil. In this study, a large-scale field experiment of applying FGD steel slag as a new amendment of saline-sodic soils was conducted in the middle Yellow River, Inner Mongolia, China. The FGD steel slag was applied at a rate of 180 t/ha in 2015, 2016, and 2018, respectively. After FGD steel slag application for 1, 3, and 4 years, the soil samples were collected. The saline-sodic field without FGD steel slag amendment was used as the control treatment (CK). Compared with control, the application of FGD steel slag significantly (p < 0.05) decreased soil pH, electric conductivity (EC), salt content, sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP) of surface soil in saline-sodic soil. However, FGD steel slag increased the EC and salt content at the lower depth of soil profile because of the salt accumulation leached from surface soil. The FGD steel slag significantly increased the concentration of Ca²⁺ and reduced the concentrations of Na⁺, Cl⁻, CO₃²⁻, and HCO₃⁻ ions. FGD steel slag was beneficial for improving adverse physical properties of saline-sodic soil. The application of FGD steel slag significantly reduced the plastic index, tensile strength, and the formation of cracking in saline-sodic soil. The FGD steel slag reduced surface area density of crack (Dc) and average crack width (AW) by 49.1% and 58.7%, compared with the control. The reduction of soil cracking was contributed to the release of Ca²⁺ from FGD steel slag to exchange the Na⁺ on the soil cation exchange sites, which decrease the clay dispersion in soil. The findings of this study confirmed that FGD steel slag could effectively and rapidly remediate saline-sodic soils through decreasing soil sodicity and improving poor physical properties.

Salt-affected soils cover a wide area, limiting agricultural production worldwide. Several remediation options are available and include chemical and vegetative remediation, but several aspects of each process are not yet fully understood. Therefore, the goal of this work was to study the application of both techniques in a highly saline scenario and provide insights into the limits of the application of this technology. Two chemical amendments (CaSO₄ and CaCl₂) and two plant species (Juncus maritimus Lam. and Spartina maritima (Curtis) Fernald) were tested to remediate a non-calcareous soil with an electrical conductivity of 20 dS m⁻¹ (EC) and a sodium adsorption ratio (SAR) of 45. Vegetative bioremediation experiments were performed under non-leaching conditions. As such, salts were redistributed and increased at the surface and decreased in depth due to capillary rise. In such conditions, there was no clear positive effect of plants on soil parameters. However, tested plants grew, accumulated, and excreted salts and sodium comparably to other research in the literature. Regardless, the obtained results suggest that plant salt uptake alone may not be sufficient for soil remediation, and therefore, other mechanisms may also play a significant role. As to chemical amendments, both chemicals used proved to be effective and reduced non-calcareous saline soil parameters to below threshold values of 4 dS m⁻¹ for EC and 7 for SAR. However, CaCl₂ was more effective and faster to remediate than CaSO₄, likely due to higher solubility. Therefore, CaCl₂ may be a viable, yet less tested, option for faster remediation processes.

Many areas throughout the world, mainly arid and semi-arid regions, are simultaneously affected by salinity stress and heavy metal (HM) pollution. Phytoremediation of such environments needs suitable plants surviving under those combined stresses. In the present study, native species naturally growing under an extreme condition, around Qaleh-Zari copper mine located in the eastern part of Iran, with HM-contaminated saline–sodic soil, were identified to find suitable plant species for phytoremediation. For this purpose, the accumulation of HMs (Cu, Zn, Cd, and Pb) in the root and shoot (stem and leaf) of the plants and their surrounding soils was determined to find their main phytoremediation strategies: phytoextraction or phytostabilization. Seven native species surviving in such extreme condition were found, including Launaea arborescens (Batt.) Murb, Artemisia santolina Schrenk, Pulicaria gnaphalodes (Vent.) Boiss, Zygophyllum eurypterum Boiss. & Buhse, Peganum harmala L., Pteropyrum olivieri Jaub. & Spach, and Aerva javanica (Burm. f.) Juss. ex Schult. Evaluation of phytoremediation potential of the identified species based on the calculated HM bioconcentration in roots, HM translocation from roots to shoots, and HM accumulation in the shoots revealed that all of the species were metal phytostabilizers rather than hyperaccumulators. Therefore, these native species can be used for phytostabilization in the HM-contaminated saline soils to prevent HMs entering the uncontaminated areas and groundwater. Compared with the biennial low-biomass hyperaccumulators, some native species such as Z. eurypterum and A. javanica may have more economic value for phytoremediation because of a significant accumulation of HMs in their relatively higher biomass.

Soil salinization has become a worldwide problem that imposes restrictions on crop production and food quality. This study utilizes a soil column experiment to address the potential of using mixed solid waste (vinegar residue, fly ash, and sewage sludge) as soil amendment to ameliorate saline-sodic soil and enhance crop growth. Mixed solid waste with vinegar residue content ranging from 60-90 %, sewage sludge of 8.7–30 %, and fly ash of 1.3–10 % was added to saline-sodic soil (electrical conductivity (EC₁:₅) = 1.83 dS m⁻¹, sodium adsorption ratio (SAR₁:₅) = 129.3 (mmolc L⁻¹)¹/², pH = 9.73) at rates of 0 (control), 130, 260, and 650 kg ha⁻¹. Results showed that the application of waste amendment significantly reduced SAR, while increasing soil soluble K⁺, Ca²⁺, and Mg²⁺, at a dose of 650 kg ha⁻¹. The wet stability of macro-aggregates (>1 mm) was improved 90.7–133.7 % when the application rate of amendment was greater than 260 kg ha⁻¹. The application of this amendment significantly reduced soil pH. Germination rates and plant heights of oats were improved with the increasing rate of application. There was a positive correlation between the percentage of vinegar residue and the K/Na ratio in the soil solutions and roots. These findings suggest that applying a mixed waste amendment (vinegar residue, fly ash, and sewage sludge) could be a cost-effective method for the reclamation of saline-sodic soil and the improvement of the growth of salt-tolerant plants.