Beta-Hydroxy-Beta-Methylbutyrate

The high pH of pristine biochar limits its application in saline-alkali soil remediation, as it may induce secondary salinization. To address this, modifying biochar to adjust its pH and enhance salt adsorption capacity is critical for improving its efficacy. Here, we conducted a pot experiment to investigate the mechanisms by which nitric acid-modified biochars improve saline-alkali soil and promote cotton seedling growth, using pristine rice straw (PRB) and maize straw biochars (PMB), and their nitric acid-modified counterparts (HRB and HMB). Compared to pristine biochar, acid-modified biochar exhibited significant reductions in total salinity content and pH, while introducing new functional groups such as N-O, quaternary-N, and pyridinic-N. The acid-modified biochar demonstrated significantly greater improvement effects on saline-alkali soil remediation and cotton plant growth than pristine biochar. Relative to the CK (non-biochar) treatment, HRB and HMB significantly reduced soil total salt by 11.10 % and 23.62 %, respectively, and reduced pH by 0.80 units and 0.60 units, respectively. Additionally, the acid-modified biochar significantly increased soil available nitrogen content and enhanced activities of C-, N-, and P-acquiring enzymes. Notably, HRB and HMB significantly increased the biomass of cotton seedlings by 19.69 % and 95.39 %, respectively, compared with the CK treatment. Furthermore, the application of acid-modified biochar also elevated photosynthetic pigment levels in plant leaves, regulated plant ion homeostasis (e.g., reduced Na⁺ accumulation and Na⁺/K⁺ ratio), and activated antioxidant systems. Thus, acid-modified biochar overcomes the limitations of pristine biochar in saline-alkali soil remediation and shows its potential as an eco-friendly restoration material.