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Salinity and acidity have affected several hundred million hectares of land throughout the globe which poses a major threat to global food security and biodiversity. Application of organic amendments for salt-affected soils has been identified as one of the most effective ways to mitigate salinity-induced problems and considered as a green technique offering twin benefits of waste load reduction and land reclamation. However, studies on reclaiming acidic-salt affected soils are limited. Therefore, this study aimed to determine the reclamation potential of biochars and organic amendments involving Gliricidia sepium biochar produced at 300 °C, 500 °C, and 700 °C, green waste compost, and municipal sewage sludge at three different amendment ratios, 1.0%, 2.5% and 5.0%. The incubation experiment was conducted for a 4-month period with different amendment ratios applied to the coastal acidic-salt affected soil. Subsamples were extracted from incubation pots after 1 and 4 months and analyzed for soil chemical parameters (pH, EC, NO 3 − , PO 4 3− , total organic carbon, cation exchange capacity, sodium adsorption ratio, exchangeable sodium percentage) and microbial enzyme activity (catalase activity, and acid-and alkaline phosphatase activity). All organic amendments demonstrated enhancement of the soil properties in a significant manner. However, increasing incubation time and amendment ratio increase the changes of soil parameters by a great percentage. Therefore, the maximum amendment ratio of 5.0% and 4 months of incubation period rendered a significant improvement in the reclamation of acidic-salt affected soil. However, the biochar produced at 500 °C contributed the maximum towards the improved physicochemical and biochemical profile of acidic-salt affected soil, making it the most promising organic amendment for the reclamation of acidic-salt affected soil. The overall reclamation efficiency of organic amendments registered the following order of variation: 700 BC < Sludge < 300 BC < Compost < 500 BC.

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Kinetic aspects of metal release were investigated to understand the effects of synthetic chelating agents (EDTA, EDDS and NTA) and low molecular weight (LMW) organic acids (oxalic and citric acids) on the release kinetics of Cr, Cu and As in chromated copper arsenate (CCA)-contaminated soil, as well as their uptake by maize (Zea mays L.). The results showed that the release of metals from soil was better described by parabolic diffusion, power function or simple Elovich model than by the first- and second-order models, indicating a heterogeneous diffusion of metals. Synthetic chelating agents afforded a higher release of Cu than that of LMW organic acids, whereas citric acid was the most effective chelating agent for Cr and As release. The most effective treatments for stimulating metal uptake in plant shoots were EDDS for Cu, EDTA for Cr, and citric acid for As, as indicated by the removal efficiencies of 0.046%, 0.036%, and 0.004%, respectively. However, Zea mays is not an attractive species for chelate-enhanced phytoremediation of CCA-contaminated soils due to its low phytoextraction rate, even in the presence of chelating agents and ligands.

Availability of water for food production is a global concern; thus, increasing water productivity has been become a necessary. Deficit irrigation is a good strategy to increase water use efficiency, but it may affect negatively on plant physiology and crop productivity. Little is known about the effect of marine algae extracts on water stress resistance and yield of onion grown on semiarid regions. Therefore, field experiments were conducted in 2018 and 2019 growing seasons to study the effect of foliar application of marine alga (Amphora ovalis) extracts (at rate of 0, 3, 6 or 9%) on onion grown under normal irrigation (80% of available soil water) or water stress (50% of available soil water). The field experiments were laid out in a split-plot design with four replicates. The highest dose of algal extract sprayed on onion grown under water stress significantly (P < 0.05) increased N, P, and K uptake by 116, 113, and 93% compared to the unsprayed plants. The application of 9% algal extract for onion grown under water stress significantly (P < 0.05) increased the bulb yield by 67 and 102%, respectively, in 2018 and 2019 growing seasons. Water stress reduced the chlorophyll production as a result of directing most of plant's energy to produce water-resistant materials such as proline and phenols. Algal extract reduced the negative effects of water stress and caused significant increases in onion growth and yield.