Cost-Effective Maize Stover Biochar Production for Enhanced Soil Carbon Sequestration

Biochar, a stable carbon(C)-rich material produced via biomass pyrolysis under oxygen-limited conditions, has become a topic of increasing scientific interest for its potential to improve soil health and sequester carbon, thereby contributing to climate change mitigation. Maize stover, a globally abundant and often underutilized agricultural byproduct, represents a promising feedstock for biochar production, facilitating waste reduction and soil improvement. However, a deeper understanding of the dynamics of maize-based biochar in soil, including its C storage potential, stability, and effect on nutrient cycling, is crucial for optimizing its application in sustainable agricultural practices. This study aimed to develop a cost-effective, highly C-efficient and accessible laboratory-scale biochar production method using readily available porcelain crucibles and a high-temperature muffle oven, with the goal of applying it to ¹³C-labelled maize stover for the creation of ¹³C-labelled biochar.

Maize stover was pyrolyzed at temperatures ranging from 250 °C to 550 °C (in 50 °C increments) for 1 hour. The impact of temperature on biochar recovery rate, pH, electrical conductivity, and molecular stability via mid-infrared spectroscopy (MIRS) was investigated. Results showed that the biochar recovery rate decreased with increasing temperature, stabilizing at ~30% at higher temperatures (>500 °C). Biochar pH increased with temperature, reaching pH ~11 and  suggesting potential implications for soil acidity amelioration. MIRS analysis indicated optimal biochar stability at around 500 °C, crucial for long-term C sequestration, based on maximized aryl-C (C=C) absorption at 1620–1540 cm⁻¹, minimized aliphatic C (C-H), and reductions in C=O stretching (1650–1800 cm⁻¹) and O-H stretching (3000–3200 cm⁻¹). Minimal variation among replicates highlights the method's high reproducibility and reliability for standardized lab-scale biochar production and comparative studies of biochar stability and soil interaction.

Further analysis, including elemental composition (C, N, H, and O), is underway to characterize the produced biochar and validate these findings. Based on these findings, the Soil and Water Management and Crop Nutrition (SWMCN) Laboratory team prepared a stable C isotope-labelled (¹³C) maize stover for biochar production. Utilizing ¹³C-labelled maize stover as feedstock will enable precise tracking of biochar-derived C in the soil, offering valuable insights into its fate and role in soil C dynamics. This isotopic labelling approach will enhance the understanding of biochar’s role in soil C cycling and support the development of evidence-based sustainable and climate-smart agricultural practices.