Recycled wheat straw biochar enhances nutrient-poor soil: Enzymatic kinetics of carbon, nitrogen, and phosphorus...

The recycling of waste wheat straw into biochar for soil improvement is a promising, sustainable strategy to enhancing nutrient-poor soils. Biochar application to soil has been shown to enhances the activity of key enzymes involved in nutrient cycling, such as invertase (INV), urease (URE), and alkaline phosphatase (ALP), which play roles in carbon (C), nitrogen (N), and phosphorus (P) cycling, as well as catalase (CAT), an enzyme with redox properties. However, the kinetic behavior of these enzymes remains largely unexplored. A 36-week laboratory study was conducted to evaluate the effects of biochar on enzyme kinetics in grey desert and aeolian soils including Michaelis-Menten constant (K_m), maximum reaction velocity (V_max), and catalytic efficiency (V_max/K_m). Results indicated that biochar application significantly increased soil pH, available phosphorus (AP), ammonium nitrogen (NH₄⁺-N), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) while reducing nitrate nitrogen (NO₃^--N), which were identified as dominant factors influencing enzyme kinetic parameters. Enzyme activities related to C, N, and P cycling (excluding catalase) increased significantly at a biochar application rate of 4 % by mass. Changes in K_m and V_max for URE, INV, ALP, and CAT suggest that biochar influences enzyme kinetics through mechanisms such as adsorption, microenvironmental shifts, and allosteric modulation. An economic assessment identified 4 % biochar application as the optimal rate, yielding soil quality index (SQI) values of 0.53 and 0.65 for grey desert and aeolian soils, respectively. These findings suggest that biochar-amended soils exhibit improved fertility, highlighting the potential of biochar to enhance soil health.