Calcium lignosulfonate, biochar, and bioorganic fertiliser synergistically improve soil quality and wheat productivity under deficit irrigation

To improve wheat productivity in water-scarce environments, soil management must enhance carbon dynamics and sustain plant processes under limited irrigation. This study examined the combined and individual effects of calcium lignosulfonate (CL), biochar (B), and bio-organic fertiliser (BOF) at two deficit irrigation levels (DI90 and DI60). The combination CL+B+BOF outperformed single or dual treatments at both levels. Compared to control, CL+B+BOF increased oxidizable carbon (EOC), total organic carbon (TOC), and dissolved organic carbon (DOC) to nearly 8 g kg⁻¹, 18 g kg⁻¹, and 350 mg kg⁻¹, respectively, showing the highest carbon content. These changes were linked to greater microbial richness (Chao1, 2,829; Shannon, 8.79) and a reshaped bacterial community with less Proteobacteria and more Actinobacteria and Bacteroidota. The best soil conditions supported high plant performance, especially under DI60. Net photosynthesis rose to 20.84 µmol m⁻²s⁻¹, and malondialdehyde levels fell to 5-6 µmol g⁻¹, indicating reduced oxidative stress. These reactions resulted in higher plant biomass, with dry and total biomass per plant of 13.86 ± 1.18 g and 32.20 ± 1.51 g, significantly above controls. SEM-EDX revealed more nitrogen and phosphorus in leaves with amendments. Multivariate analysis showed that soil carbon, microbial traits, and photosynthesis explained about 93% of the variation in plant performance. Overall, using CL, biochar, and BOF together improves wheat productivity and water-use efficiency under severe water deficits. • Lignin amendments under deficit irrigation elevated soil pH and organic carbon level of acidic soil. • Lignin amendments increased bacterial community structure. • Microscopy/SEM–EDX showed better wheat growth and improved plant nutrition with combined amendments. • Lignin amendments boosted photosynthesis, and antioxidants, improving drought tolerance of wheat.