The development of new approaches for sustaining soil quality, leaf health, and maize productivity are imperative in light of water deficit and soil salinity. Plant growth-promoting rhizobacteria (PGPR) and silica nanoparticles (SiNP) are expected to improve soil chemistry leading to improved plant performance and productivity. In this field experiment, water deficit is imposed by three irrigation intervals—12 (I₁), 15 (I₂), and 18 (I₃) days. Plants are also treated with foliar and soil applications (control, PGPR, SiNP, and PGPR + SiNP) to assess soil enzymatic activity, soil physicochemical properties, plant physiological traits, biochemical analysis, nutrient uptake, and productivity of maize (Zea mays L.) plants grown under salt-affected soil during the 2019 and 2020 seasons. With longer irrigation intervals, soil application of PGPR relieves the deleterious impacts of water shortage and improves yield-related traits and maize productivity. This is attributed to the improvement in soil enzymatic activity (dehydrogenase and alkaline phosphatase) and soil physicochemical characteristics, which enhances the plants’ health and growth under longer irrigation intervals (i.e., I₂ and I₃). Foliar spraying of SiNP shows an improvement in the physiological traits in maize plants grown under water shortage. This is mainly owing to the decline in oxidative stress by improving the enzymatic activity (CAT, SOD, and POD) and ion balance (K⁺/Na⁺), resulting in higher photosynthetic rate, relative water content, photosynthetic pigments, and stomatal conductance, alongside reduced proline content, electrolyte leakage, lipid peroxidase, and sodium content under salt-affected soil. The co-treatment of SiNP with PGPR confirms greater improvement in yield-related traits, maize productivity, as well as nutrient uptake (N, P, and K). Accordingly, their combination is a good strategy for relieving the detrimental impacts of water shortage and soil salinity on maize production.

Plant growth and crop productivity under unfavorable environmental challenges require a unique strategy to scavenge the severely negative impacts of these challenges such as soil salinity and water stress. Compost and plant growth-promoting rhizobacteria (PGPR) have many beneficial impacts, particularly in plants exposed to different types of stress. Therefore, a field experiment during two successive seasons was conducted to investigate the impact of compost and PGPR either separately or in a combination on exchangeable sodium percentage (ESP), soil enzymes (urease and dehydrogenase), wheat physiology, antioxidant defense system, growth, and productivity under deficient irrigation and soil salinity conditions. Our findings showed that exposure of wheat plants to deficit irrigation in salt-affected soil inhibited wheat growth and development, and eventually reduced crop productivity. However, these injurious impacts were diminished after soil amendment using the combined application of compost and PGPR. This combined application enhanced soil urease and dehydrogenase, ion selectivity, chlorophylls, carotenoids, stomatal conductance, and the relative water content (RWC) whilst reducing ESP, proline content, which eventually increased the yield-related traits of wheat plants under deficient irrigation conditions. Moreover, the coupled application of compost and PGPR reduced the uptake of Na and resulted in an increment in superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) activities that lessened oxidative damage and improved the nutrient uptake (N, P, and K) of deficiently irrigated wheat plants under soil salinity. It was concluded that to protect wheat plants from environmental stressors, such as water stress and soil salinity, co-application of compost with PGPR was found to be effective.

Water deficit stress can negatively affect oil quality, crop yields and soil infertility. Thus, we investigated the effects of rice-straw biochar, foliar silicon and their combination on quality, yield and physiological traits of sunflower grown under three water deficit stress treatments. Water stress treatments were 50% (WS₀; no stress), 70% (WS₁; moderate stress) and 90% (WS₂; severe stress) depletion of the available soil moisture. The results showed that WS₁ and WS₂ negatively affected oil quality, mycorrhizal spores, yield and physiological traits of the sunflower; however, biochar, silicon and their combination significantly (p ≤ 0.05) improved most of those traits. Oil and oleic acid contents of sunflower grown under WS₂ were decreased by 18% and 25.8% compared to those grown under WS₀, respectively. Nevertheless, the biochar and silicon combination resulted in higher oil (10.2%) and oleic acid (12.2%) in plants grown under WS₂ than those grown in untreated plots. Also, a significant increase (182% and 277%) in mycorrhizal spores was obtained in soil treated combination of biochar and silicon under WS₁ and WS₂ in comparison to untreated soil, respectively. On the other hand, plants grown under WS₁ and WS₂ exhibited reduced seed yield ha⁻¹ by 16.5% and 53.5% compared to those grown under WS_0, respectively. However, seed yield ha⁻¹ were increased by 26.8% and 27.1% in plots treated with combined treatment compared to untreated plants, respectively. In addition, the biochar and silicon combination significantly increased stomatal conductance by 21.4% and 12.1%, reduced proline by 56.6% and 51.2% and reduced catalase activity by 13.4% and 17.3% under WS₁ and WS₂ compared to those grown in untreated plots, respectively. Therefore, the combined treatment of biochar and silicon can minimize and alleviate the negative effects of WS₁ and WS₂, improve oil quality, physiological traits, microbial activity and seed yield ha⁻¹ in sunflower plants.

Environmental stressors negatively affect crop growth and yield. Limited information is available about the synergistic use of biochar and plant growth-promoting rhizobacteria (PGPR). A field study was conducted to evaluate the effect of biochar in combination with PGPR (Pseudomonas koreensis and Bacillus coagulans) for alleviating water deficit and saline soil in rice (Oryza sativa L.). Two growing seasons, 2017 and 2018, were examined using twelve combinations of three irrigation intervals every 6 days (I₁), 8 days (I₂), and 10 days (I₃) and four soil treatments (control, PGPR, biochar, and combination of PGPR + biochar) in salt-affected soil. The findings exhibited that synergistic use of biochar and PGPR alleviated the negative effect of these stressors. The integrative use of biochar and PGPR caused an increment in soil moisture content and physicochemical properties. Significant increasing in chlorophyll content, relative water content, stomatal conductance, K⁺ and K⁺/Na⁺ contents occurred with decreasing proline content and Na⁺ content, which confirmed the efficacy of this approach. As a result, the highest yield and its related traits were attained when biochar and PGPR were added together under irrigation interval I₁, which was on par with I₂. We concluded that increased nutrients uptake (N, P, and K) were the cause of the superior rice productivity resulting from co-PGPR biochar. Synergistic use of biochar and PGPR could be an effective strategy for improving plant growth and productivity under stressors.

The utilization of low-quality water or slightly saline water in sodic-saline soil is a major global conundrum that severely impacts agricultural productivity and sustainability, particularly in arid and semiarid regions with limited freshwater resources. Herein, we proposed an integrated amendment strategy for sodic-saline soil using biochar and/or plant growth-promoting rhizobacteria (PGPR; Azotobacter chroococcum SARS 10 and Pseudomonas koreensis MG209738) to alleviate the adverse impacts of saline water on the growth, physiology, and productivity of maize (Zea mays L.), as well as the soil properties and nutrient uptake during two successive seasons (2018 and 2019). Our field experiments revealed that the combined application of PGPR and biochar (PGPR + biochar) significantly improved the soil ecosystem and physicochemical properties and K⁺, Ca₂⁺, and Mg₂⁺ contents but reduced the soil exchangeable sodium percentage and Na⁺ content. Likewise, it significantly increased the activity of soil urease (158.14 ± 2.37 and 165.51 ± 3.05 mg NH₄⁺ g⁻¹ dry soil d⁻¹) and dehydrogenase (117.89 ± 1.86 and 121.44 ± 1.00 mg TPF g⁻¹ dry soil d⁻¹) in 2018 and 2019, respectively, upon irrigation with saline water compared with non-treated control. PGPR + biochar supplementation mitigated the hazardous impacts of saline water on maize plants grown in sodic-saline soil better than biochar or PGPR individually (PGPR + biochar > biochar > PGPR). The highest values of leaf area index, total chlorophyll, carotenoids, total soluble sugar (TSS), relative water content, K⁺ and K⁺/Na⁺ of maize plants corresponded to PGPR + biochar treatment. These findings could be guidelines for cultivating not only maize but other cereal crops particularly in salt-affected soil and sodic-saline soil.

The continuity of traditional planting systems in the last few decades has encountered its most significant challenge in the harsh changes in the global climate, leading to frustration in the plant growth and productivity, especially in the arid and semi-arid regions cultivated with moderate or sensitive crops to abiotic stresses. Faba bean, like most legume crops, is considered a moderately sensitive crop to saline soil and/or saline water. In this connection, a field experiment was conducted during the successive winter seasons 2018/2019 and 2019/2020 in a salt-affected soil to explore the combined effects of plant growth-promoting rhizobacteria (PGPR) and potassium (K) silicate on maintaining the soil quality, performance, and productivity of faba bean plants irrigated with either fresh water or saline water. Our findings indicated that the coupled use of PGPR and K silicate under the saline water irrigation treatment had the capability to reduce the levels of exchangeable sodium percentage (ESP) in the soil and to promote the activity of some soil enzymes (urease and dehydrogenase), which recorded nearly non-significant differences compared with fresh water (control) treatment, leading to reinstating the soil quality. Consequently, under salinity stress, the combined application motivated the faba bean vegetative growth, e.g., root length and nodulation, which reinstated the K⁺/Na⁺ ions homeostasis, leading to the lessening or equalizing of the activity level of enzymatic antioxidants (CAT, POD, and SOD) compared with the controls of both saline water and fresh water treatments, respectively. Although the irrigation with saline water significantly increased the osmolytes concentration (free amino acids and proline) in faba bean plants compared with fresh water treatment, application of PGPR or K-silicate notably reduced the osmolyte levels below the control treatment, either under stress or non-stress conditions. On the contrary, the concentrations of soluble assimilates (total soluble proteins and total soluble sugars) recorded pronounced increases under tested treatments, which enriched the plant growth, the nutrients (N, P, and K) uptake and translocation to the sink organs, which lastly improved the yield attributes (number of pods plant⁻¹, number of seeds pod⁻¹, 100-seed weight). It was concluded that the combined application of PGPR and K-silicate is considered a profitable strategy that is able to alleviate the harmful impact of salt stress alongside increasing plant growth and productivity.