Synergistic effect of biochar along with gypsum and foliar nutrient strategies on the growth, yield, metabolism and gene expression in barley under salinity stress.

Soil salinity considerably limits agricultural production, thus harming food security worldwide. To evaluate the effects on barley yield in salt-affected soil, biochar (BC) and gypsum (GS) were applied individually and in combination. These soil amendments were further supplemented with various foliar treatments, including water misting, proline (Pr), iron (Fe), and silica (Si), applied alone or in different combinations over two consecutive growing seasons. The results showed that BC + GS treatment increased the plant height (13.71 %), spike length (20.61 %), biological yield (22.14 %), and grain yield (20.07 %) of barley. The application of BC + GS to soils increased the K% levels in barley grains during both seasons (23 % and 23.3 %, respectively) as compared to the control (CK). Additionally, BC + GS treatments resulted in an elevated K/Na ratio in soil by 53.57 % and 58.62 % respectively during the two seasons. Similarly, combining foliar agents (Pr + Fe + Si) and BC + GS significantly improved the K% and K/Na ratio in the soil. Notably, our study shows that BC + GS lowered the electrical conductivity of the saturation extract (ECe) and the exchangeable sodium percentage (ESP) in post-harvest soil relative to the pre-treatment values. The reduction in ECe and ESP is a key indicator of improved conditions in salt-affected soils, signaling lower salinity and sodicity. SOD and CAT activities were significantly increased to 1.8-2.21-fold and 1.76-2.29-fold, respectively, when BC + GS was combined with Pr + Fe + Si across both the seasons. Gene-expression analysis revealed up-regulation of sodium/proton exchangers (NHX1, NHX2) and the K transporter HAK1, which help to maintain ion and pH balance under salinity stress. Additionally, transcript levels of antioxidant enzymes (HvCAT1, HvSOD1, HvAPX, HvGR1, and HvGR2) increased, further mitigating salt-induced oxidative damage. BC + GS therefore mitigates salinity stress, enriches nutrient status and improves barley yield. Long-term, IoT-assisted field monitoring and genotype × treatment (G × T) trials can be helful to validate and optimise these benefits across diverse production environments particularly in adopting the mitigating strategies in salinity stressed barley.