A Comprehensive Review of the Biochar-Mediated Alleviation of Salt Stress

Salt stress remains a major global stress factor among abiotic stresses limiting crop production. Salt stress is a major nutritional challenge, with poor agricultural production characterized by high soil sodium (Na⁺) levels in soil and plants. Soil salinity negatively affects plants through both osmotic effects and ionic toxicity. Hence, one of the main aims of agricultural scientists is to develop eco-friendly, sustainable solutions to alleviate soil salinity. Over the past decades, several studies have recommended biochar as a vital sustainable soil amendment to alleviate the negative consequences of soil salinity. Thus, this review builds on the literature on biochar-mediated alleviation of salt stress. Biochar is a carbon-rich material produced from biomass and feedstock via pyrolysis under little or no oxygen conditions. Due to its unique characteristics, such as high carbon, high surface area with porous and aromatic structure, high pH, high stability, cation exchange capacity, and water and nutrient retention capacity, it is considered an alternative for salt stress alleviation. Moreover, biochar facilitates sodium ion (Na⁺) adsorption, reduces Na⁺ uptake, and increases potassium ion (K⁺) uptake, enhancing nutrient cycling, helping plants maintain ionic balance and osmotic regulation. This, in turn, significantly increased the activity and diversity of soil microorganisms, enhanced their adhesion, and promoted their growth, thereby strengthening the plant's salt resistance. Moreover, biochar-mediated improvements in microbial community dynamics and changes in the physical and biological properties of soil contribute to overall plant and soil health under salt stress. Hence, the present review aims to decipher the holistic patterns of biochar on soil and plant health, changes in physiological and defense mechanisms, plant hormones and signaling mechanisms, and the status of modified biochar under salt stress. Thus, the present review will pave the way for the production of salt-resilient crops with enhanced salinity tolerance. In conclusion, the use of biochar-based fertilizers and modified biochar enhanced microbial community dynamics in soil health homeostasis and soil fertility for agricultural production and food security.