The disposal of coal fly ash (CFA) generated from coal-fired power stations has serious impact on the ecosystem, by converting large pieces of land to barren ash dams with the potential to contaminate groundwater, surface water, air and soil. The aim of this study was to clarify the potential of phytoremediation using Helichrysum splendidum (Thunb.) Less. in areas polluted by CFA through conduction of pot trial experiments for 14 weeks. Plants of the same age were cultivated in CFA to assess their growth, photosynthetic rate and tolerance towards metal toxicity. This study revealed that the CFA was moderately polluted with heavy metals, and a lower photosynthetic rate was recorded for the CFA plants in comparison to the controls (plants grown in soil). Although the CO₂ assimilation rate was lower for the CFA plants, increased growth was recorded for all the plants tested. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the amount of trace elements in samples and parameters including translocation factor (TF) and bioconcentration factor (BCF) were used to evaluate the phytoremediation potential of H. splendidum (Thunb.) Less. The results revealed that higher concentrations of Cd, Co, Cr, Cu, Mn and Pb were accumulated in the roots, while As, Ni and Zn were found in the shoots. Elements including As, Cr and Zn reported TF values above 1, indicating the plants’ phytoextraction potential. The BCF values for As, Cu and Zn were 1.22, 1.19 and 1.03, indicating effectiveness in the phytostabilization processes. A removal rate efficiency ranging from 18.0 to 56.7% was recorded confirming that, H. splendidum (Thunb.) Less. can be employed for restoration of CFA dams.

The benefits of legume-nitrogen-fixing bacteria symbioses are vital in agricultural systems globally. Cross-infectivity studies are important for identifying rhizobial strains with potential for use as inoculants. The native rhizobial isolates inoculated on different legume species are the first step to determining host range and ecological adaptive traits. This study reports on the water-use efficiency and mineral nutrition of diverse legume species cross-inoculated by native rhizobial isolates from Eswatini, Ghana and South Africa under glasshouse conditions. A portable infrared red gas analyzer was used for water use efficiency. Data from a gas exchange study shows that rhizobial strains can significantly influence the photosynthetic functioning of their host plants. As a result, photosynthetic rates differed depending on bacterial compatibility with the host plant, as well as its symbiotic efficacy. Isolate TUTGmGH2 induced greater accumulation of P, K, Mg, Zn, Cu and Mn in soybean and Winged bean, clearly suggesting that rhizobia do have an influence on the mineral nutrition of their host plants. Therefore, these findings further show that native rhizobial isolates can be manipulated to enhance mineral nutrient uptake, promote growth and development and also produce nutrient-dense food with a low environmental impact globally since rhizobia do have an influence on the mineral nutrition of their host plants.

Legume crops, such as the common bean (Phaseolus vulgaris L.), are significant in many Sub-Saharan African (SSA) countries, including Eswatini, due to their numerous health benefits, including high protein, fiber, vitamins, and mineral content. Common beans are a staple food in many parts of the world and play a crucial role in nitrogen fixation, thereby improving soil fertility. A field experiment was conducted at Malkerns research station, Eswatini, using 27 common bean genotypes to assess their ability for N-fixation and water relations using the ¹⁵N and ¹³C natural abundance techniques. The data revealed significant differences among the common bean genotypes. Genotypes Cim-Rm-36 and Mwctz20a-Rm19 recorded an increase in plant growth by (6% and 5.74%), N content (5.69% and 5.97%) and greater C content (6.1% and 5.67%) while genotype Mwctz20a-Rm19 also showed an increase in N-fixation (155.73 kg.ha⁻¹). Genotype Mwctz20a-Rm-4 had the highest grain yield (1747.39 kg.ha⁻¹), while genotype Cim-Rm-14-Als61 had the highest N concentration (3.50%), indicating efficient N uptake. The genotypes with the lowest δ¹³C values (−27.38‰ to −28.06‰) suggested similar water use efficiency among the genotypes. The findings of this study revealed that common beans can make a significant contribution to N fertility under drought conditions. Genotypes Cim-Rm-36, Mwctz20a-Rm19, and Mwctz20a-Rm-4 showed desirable characteristics and can be good candidates for possible inclusion in breeding programs. These results have implications for improving common bean production in drought-prone areas and promoting sustainable agriculture practices.

Herbicide use in legume-based cropping systems raises concerns about potential disruption of the rhizobium-legume symbiosis essential for biological nitrogen fixation (BNF). This study evaluated the effect of herbicide-treated soil inoculum on plant growth, nodulation, and symbiotic nitrogen fixation in cowpea (Vigna unguiculata L. Walp.) and soybean (Glycine max L. Merr.) under glasshouse conditions. Soil samples were collected from paired herbicide-treated (≥3 years of application) and untreated (≥6 years without herbicides) fields across fifteen locations in the Upper West Region of Ghana and used as inocula for cowpea (cv. Kirkhouse) and soybean (cv. Favour) grown in sterilised sand. Results showed that herbicide-treated soils had significantly higher available phosphorus, iron, calcium, zinc, and soil organic carbon than untreated soils (p < 0.01). However, no significant overall differences (p ≥ 0.05) were detected between herbicide-treated and untreated soil inocula for nodule number, N-fixed, or whole-plant dry matter in either legume. Location was the predominant determinant of nodulation and symbiotic effectiveness (p ≤ 0.001). A significant location × soil type interaction for soybean nodulation indicated site-specific herbicide sensitivity among Bradyrhizobium populations. Herbicide type × legume interactions revealed differences in effects, with specific formulations selectively reducing symbiotic parameters in either cowpea or soybean. Cowpea exhibited consistently superior nodulation and nitrogen fixation relative to soybean across all treatments. These findings demonstrate that indigenous rhizobial populations in the study area retain functional symbiotic capacity despite prolonged herbicide exposure, though herbicide-specific and location-dependent effects warrant consideration in integrated weed management strategies for grain legumes.

Leguminous crops contribute approximately 40–60 million tonnes of biologically fixed nitrogen annually to agricultural soils through symbiotic associations with rhizobia, underpinning the sustainability of diverse cropping systems. However, rising herbicide use, driven by the adoption of herbicide-tolerant crops and intensifying weed resistance, poses significant threats to the integrity of the legume–rhizobia symbiosis, depending on the herbicide type, exposure level, soil conditions, and microbial variability. This review synthesizes possible herbicide-induced disruptions of symbiotic nitrogen fixation, including herbicide impairment of symbiosis through multiple interconnected pathways, such as cytotoxicity to rhizobia and soil microbial communities, inhibition of nod-gene-inducing flavonoid biosynthesis by the host plant, suppression of Nod factor production and signalling by rhizobial disruption of cytoskeletal functioning that enhances the progression of infection thread formation, oxidative stress induction, alterations of auxin–cytokinin homeostasis, and modification of soil physicochemical parameters that can affect rhizobial survival and competitiveness. Though still unclear, laboratory (in vitro), field and glasshouse studies suggest that symbiotic impairment is dose- and time-dependent, species-specific, and strongly influenced by the rhizobial strain and probably the host plant species variety. Mitigation strategies, such as the use of herbicide-tolerant rhizobial strains, organic soil amendments, optimized herbicide application, and integrated weed management frameworks, have shown considerable promise. However, many research gaps exist regarding tropical legume systems and the long-term consequences of herbicide use on the legume–rhizobia symbiosis. Little is known about the direct effects of herbicides on the bacterial symbionts and host plants, as well as how soil type, climate and management/agronomic practices influence herbicide exposure and the effect of herbicide degradation products on rhizobial survival, competitiveness, and symbiotic N₂-fixation. The existence of herbicide-tolerant soybean suggests that not all herbicides are lethally phytotoxic, an aspect that can be exploited for sustainable agriculture.