Abstract:
China produces a substantial amount of crop straw annually, and improper disposal, management, and burning in fields poses significant threats to water and atmospheric environmental quality. Straw return to the field is currently the primary way for addressing the environmental risks posed by crop straw. Based on its purpose, straw return can be categorized into two types: direct in-situ return, aimed at on-site straw disposal, and crop growth barrier-eliminating relocated return, designed to mitigate crop growth constraints. However, neither approach utilizes the bioenergy potential of straw. While they may enhance soil organic matter content to some extent, their effects are limited and lack significant cumulative benefits over time. The bioenergy of straw is utilized if straw is transferred into biogas through anaerobic fermentation in biogas digester, but its implementation is challenging due to factors such as unstable gas production and difficulties in treating the residue and liquid byproducts. This study proposes a novel straw management way, termed the "Space-time Integration of Soil Improvement and Energy Production by Using Straw" (ISES), which simultaneously achieves soil improvement and energy production within the same time and spatial framework. Specifically, ISES involves applying crop straw collected around to the soils requiring remediation at a rate exceeding 5% of the soil weight, thoroughly mixing it with soil, and conducting sealed anaerobic fermentation under flooded conditions. The biogas generated from this process can be collected for household fuel or other applications. The ISES method can significantly enhance soil organic matter across fertility gradients. Its gas production and methane (CH
4) concentration are comparable to traditional biogas fermentation, without the need to handle biogas residues or slurry. It serves multiple objectives: soil improvement, bioenergy production, and carbon sequestration. Thus, further research is needed to: 1) investigate carbon transformation and methane production processes in the ISES system; 2) examine factors influencing gas yield and CH
4 concentration; 3) assess the environmental effects during and after ISES treatment. Such studies are also essential for optimizing the treatment process, identifying suitable soil types and treatment timings for ISES, mitigating environmental impacts, establishing safety measures, and evaluating economic feasibility.