The disposal of crop residues from agricultural fields is often seen as a burden due to the difficulties involved. However, this study aims to turn pigeonpea stalks into biochar, which can serve as a fuel substitute and soil amendment to sequester carbon. Different pyrolysis methods were employed to investigate the variations in yield, physicochemical characteristics, and higher heating value (HHV) of biochar produced from pigeonpea stalks. The biochar produced using a muffle furnace exhibited higher fixed carbon and ash content. These characteristics make it beneficial for restoring degraded agricultural soils by enhancing carbon sequestration. In addition, the muffle furnace biochar demonstrated a total potential carbon ranging from 262.8 to 264.3 g of carbon per kilogram of biochar, along with a CO₂ reduction potential ranging from 77.17 to 79.68 CO₂ eq per kg. Both the European Biochar Certificate and the International Biochar Initiative confirmed the agronomic abilities of the biochar and its compliance with the highest quality standards for soil carbon sequestration, with 0.11 H/C and 0.7 O/C ratios. Furthermore, biochar produced by muffle furnace from pigeonpea stalks exhibited superior fixed carbon recovery efficiency (181.66 to 184.62%), densification (5.86 to 6.83%), energy density (1.77 to 2.06%), energy retention efficiency (54.80 to 56.64%), fuel ratio (18.95 to 22.38%), and HHV (30.66 to 32.56 MJ kg⁻¹). Additionally, it had lower H/C and O/C ratios, suggesting its potential as an alternative solid fuel. The results of the characterization of biochar with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) revealed that the biochar samples prepared with both the methods had carbonyl (C=O), C=C, and aromatic C-H functional groups; however, the biochar prepared in the muffle furnace had more porosity. In summary, this study highlights the potential of using pigeonpea stalks to produce biochar, which can be utilized as a renewable fuel substitute and soil amendment to sequester carbon. The biochar derived from the muffle furnace exhibited desirable physicochemical characteristics, high carbon content, and excellent energy properties, making it a promising option for various applications.

Accurate accounting of global methane remains a critical challenge, with rice cultivation contributing significantly to uncertainties in global methane budgets. Both top-down and bottom-up approaches still largely depend on emission factors and census data. In this review, we synthesize current knowledge from global estimates made between 1963 and 2025, which range from 10 to 280 Tg/yr, with more recent estimates differing by about 4 Tg/yr and having a coefficient of variation of 13%. We examined these approaches, identified their limitations, and found that nearly 67% of available global estimates are based on bottom-up methods, while 33% use top-down approaches. We see substantial disparities among rice-producing countries, with the top ten countries by harvest area accounting for 85% of rice production (81% of global harvested area) and 83% of methane emissions, primarily in South and Southeast Asia. Although overall emissions are increasing due to the expansion of rice cultivation, emission intensity has declined in most major countries, indicating a somewhat positive outlook. Advances such as global rice inventories, improved satellite technologies and process-based models, phenology-based crop mapping, and low-methane-emitting rice varieties offer promising prospects for more accurate future estimates.