Effects of incorporating biochar on soil quality and barley yield in microplastics-contaminated soils

Biochar has been recognized for its potential to improve the fertility soils by reducing the reliance on chemical fertilizers, mitigating carbon emissions, and fostering soil microbial growth. This study aimed to evaluate the impact of biochar addition on the physicochemical properties of arid and semi-arid soils containing microplastics, while also assessing its effect on Barley (Hordeum vulgare) yield under drought stress. The experiment was conducted in a glass greenhouse. Plastic pots containing 3 kg of soil were each planted with 6 barley grains. Biochar was applied at three doses (B0 = 0 g biochar/kg soil, B1 = 6 g biochar/kg soil, B2 = 10 g biochar/kg soil), while microplastics were added at three levels (M0 = Control without microplastics, M1 = 0.5 g/kg soil, and M2 = 1 g/kg soil) on the same sowing date. Water stress was induced when the plants reached the four-leaf stage. ANOVAs and Tukey post-hoc tests were employed for multiple mean comparisons of soil and plant parameters. Drought stress and microplastics negatively influenced soil parameters namely soil moisture, organic carbon, and nitrates, while also affecting electrical conductivity and pH. Biochar exhibited minimal effect on soil properties but significantly altered pH, nitrates, and total CaCO₃. Plant chlorophyll levels decreased under stress, particularly with microplastic dose M1. However, biochar and microplastics enhanced chlorophyll a content, except for dose B1 of biochar, which leads to a decrease in chlorophyll b (0.91 ± 0.138 μg/g FM). Microplastics, at dose M2, improved chlorophyll b content (1.11 ± 0.090 μg/g FM). Aboveground biomass, leaf area, and yield were generally unaffected by tested stresses. Nonetheless, barley grain yield decreased in biochar and microplastic dose M1 (0.47 ± 0.108 g/plant), while it improved with microplastic dose M2 (0.65 ± 0.168 g/plant). Leaf relative water content increased under water stress and microplastics but not with biochar alone. Interaction between microplastics and biochar enhanced plant water content. Drought stress and microplastics diminished soil parameters, whereas biochar lowered nitrates and pH without significantly affecting soil organic carbon. Plant productivity parameters generally exhibited no significant change under water stress, microplastics, or biochar, except for yield and chlorophyll pigments.