Pyrolysis temperature regulates biochar-soil interactions to enhance cation exchange capacity, plant growth, and photosynthetic performance

Poor nutrient retention in agricultural soils limits crop productivity and fertilizer use efficiency. Enhancing the soil capacity to retain cations such as Ca 2 ⁺, Mg 2 ⁺, and K⁺ is critical for sustaining plant nutrition, yet strategies that simultaneously improve cation availability and crop performance remain underexplored. This study investigated a pyrolysis temperature dependent biochar strategy to improve nutrient retention and plant performance by integrating urea with biochar produced at 300, 500, and 700 °C. The effects of urea alone (UA) and biochar produced at 300, 500, and 700 °C, blended with urea (BB300, BB500, BB700), and impregnated with urea (IB300, IB500, IB700), were evaluated in a soil–plant system of water spinach. Among all treatments, IB500 was the most effective, significantly improving key soil properties, including cation exchange capacity (CEC), and the availability of Ca 2 ⁺, Mg 2 ⁺, and K⁺, while increasing microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). These soil improvements promoted substantial enhancements in root system architecture; IB500 resulted in a 56% increase in root length, an 81% increase in surface area, and a 91% increase in root tip formation compared to urea alone. The robust root system facilitated more vigorous shoot development, including a 33% increase in leaf number, a 59% increase in leaf area index, and a 44% increase in chlorophyll content. Physiologically, IB500 treated plants exhibited a 12% higher photosynthetic rate, a 13% increase in stomatal conductance, and a 79% increase in nitrogen uptake. Biochar pyrolyzed at 500 °C and impregnated with urea showed strong potential as a multifunctional soil amendment, enhancing nutrient retention, soil fertility, and plant physiological performance. These findings identify pyrolysis temperature as a key regulator of biochar, soil, and nutrient interactions, offering a mechanistic and sustainable strategy to improve crop productivity through rhizosphere optimization. Pyrolysis modified biochar integrated with urea enhances soil cation exchange capacity (CEC), retaining essential cations (Ca²⁺, Mg²⁺, and K⁺). This improved soil environment promotes root development, microbial activity, and ultimately increases shoot biomass, chlorophyll content (SPAD), and net photosynthesis rate (Pₙ) compared to urea alone.