添加稻稈於土壤生態瓶、土壤管柱以及現地不同深度的土壤碳降解變化

Abstract

面對氣候變遷挑戰，農業應用上有許多方式來對抗，例如含碳農業剩餘物還田、不整地栽培以及輪作等，如何巧妙應用農業技術進行土壤儲碳已成為提升土壤品質與永續利用的重要課題。臺灣目前對農餘物還田多採表層還田方式 (0-30 cm)，但在表層微生物活性旺盛與環境變動頻繁的條件下，農餘物常迅速分解，釋出大量溫室氣體 (Greenhouse Gases, GHGs)，不利於長期土壤有機碳 (Soil Organic Carbon, SOC) 累積與形成穩定碳。相較之下，深層土壤因氧氣供應較少、微生物活性較低等特性，有潛力延緩分解，使農餘物得以在土壤中存留更久。本研究方向以稻稈作為還田資材，觀察生態瓶添加硫化鐵 (FeS) 後GHGs的排放以及模擬管柱、現地試驗之稻稈於不同深度 (表層至深層) 埋設後的分解速率差異。 在生態瓶試驗中，分別添加不同比例的FeS以探討其在土壤碳穩定與GHGs排放控制上的潛力。FeS具有良好的氧化還原能力，可在厭氧條件下作為電子受體。試驗結果顯示，越高比例FeS的添加抑制了甲烷 (CH4) 的生成，顯示 FeS 可有效地競爭電子，減緩溫室氣體排放，進而降低碳損失。 管柱試驗中，稻稈分別埋設於30-50、80-100與140-160 cm深度，並定期分析稻稈碳含量變化，應用一階動力學模型估算分解速率常數 (k值)。結果顯示，稻稈在表層 30 cm 處的分解速率最高，k值為0.088 month-1；中層80-100 cm處為0.030 month-1；最深層140-160 cm處則為0.025 month-1，顯示深層處理能有效減緩有機質分解。此一分解速率差異與土壤環境因子密切相關。表層處理 (30-50 cm) 具有較高的氧化還原電位 (Oxidation-Reduction Potential, ORP) 伴隨著較高GHGs排放與Shannon多樣性指數，顯示此處具較強的好氧微生物活性，促進稻稈的快速分解。相對地，較深層的兩個處理 (80-100 cm、140-160 cm) 中，ORP顯著下降、土壤含水量 (Soil water content, SWC) 升高，反映出更強的還原性環境，有助於厭氧菌生長，但整體GHGs排放量與Shannon指數下降，這些環境條件共同限制了深層土壤對稻稈的分解效率，使其有機碳得以在土壤中保存較長期 。 在現地試驗部分，將稻稈分別埋設於 30、60 及90 cm 深度，並持續觀察稻稈碳變化。結果顯示，30 cm處理之分解速率最高為0.33 month-1，而60 cm與90 cm處理之速率常數皆為0.04 month-1，與管柱試驗結果一致，進一步驗證深層埋入可有效延緩有機質分解並提升碳封存潛力。各處理土壤性質亦呈現差異，深層埋設處理相較於淺層具有較高之SOC與SWC，而表層處理則與較高的GHGs排放有關，顯示稻稈埋設深度對碳循環與土壤環境條件具有顯著影響。 在微生物群落分析方面，管柱中30-50cm埋入處理中以Bacillus、Ruminiclostridium與Anaerocolumna為優勢菌屬，屬於具纖維素分解能力之需氧或兼性厭氧菌，反映表層稻稈易被分解的特性。相對地，80-100 cm 及 140-160 cm 深層處理則以厭氧發酵菌Caproiciproducens為主，且群落組成展現出更強烈的厭氧代謝特徵，顯示不同深度調控了微生物多樣性與功能性表現。現地試驗結果亦佐證深層稻稈埋入可顯著提升微生物多樣性，有助於形成具穩定性的微生物碳循環系統。 綜合以上所述，將稻稈掩埋於土壤深層，能有效延緩其分解速率，深層掩埋不僅能提升土壤碳的滯留時間與穩定性，更能減緩溫室氣體排放風險，值得進一步推廣與深入研究。

Facing the challenges of climate change, various agricultural practices—such as the incorporation of crop residues, no-tillage, and crop rotation—have been adopted to mitigate greenhouse gas (GHG) emissions. Among these, enhancing soil carbon sequestration has become critical for improving soil quality and sustainability. In Taiwan, surface incorporation of crop residues (0-30 cm) is common; however, due to active microbial processes and environmental fluctuations at the surface, residues rapidly decompose, releasing GHGs and hindering long-term soil organic carbon (SOC) accumulation. In contrast, deeper soil layers—with lower oxygen and microbial activity—may delay decomposition and prolong carbon retention. This study investigated rice straw carbon mineralization dynamics at different soil depths through microcosm, column, and field experiments, including the use of iron sulfide (FeS) as a potential GHG mitigation agent. In microcosms, increasing FeS addition suppressed methane (CH4) emissions, indicating FeS effectively acts as a competitive electron acceptor under anaerobic conditions, reducing carbon losses. In soil column trials, rice straw was buried at 30-50, 80-100, and 140-160 cm. First-order kinetic modeling revealed the highest decomposition rate at 30-50 cm (k = 0.088 month-1), followed by 80-100 cm (k = 0.030 month-1) and 140-160 cm (k = 0.025 month-1). Surface soils exhibited higher oxidation-reduction potential (ORP), greater GHG emissions, and higher microbial diversity (Shannon index), reflecting aerobic conditions favorable for rapid decomposition. In contrast, deeper soils showed reduced ORP and increased soil water content (SWC), indicating more reductive environments conducive to anaerobic conditions and slower decomposition. Field trials supported these results. Rice straw was buried at 30, 60, and 90 cm, and decomposition rates were highest at 30 cm (k = 0.33 month-1), while both 60 and 90 cm depths showed significantly lower rates (k=0.04 month-1).Deep burial treatments also exhibited higher SOC and SWC, while surface treatments were associated with greater GHG emissions, underscoring the environmental impact of burial depth. Microbial community analysis from the column experiment revealed that surface soils (30-50 cm) were dominated by cellulolytic aerobic and facultative anaerobic genera such as Bacillus, Ruminiclostridium, and Anaerocolumna. In contrast, deeper layers were dominated by the anaerobic fermentative genus Caproiciproducens, with microbial profiles indicating more pronounced anaerobic metabolic functions. Field results further confirmed that deep burial enhances microbial diversity and contributes to more stable microbial carbon cycling. In conclusion, deep burial of rice straw effectively slows decomposition, prolongs SOC residence time, and reduces GHG emissions. This approach offers significant potential for carbon sequestration and merits broader application in sustainable agriculture.