紫色土丘陵区保护性耕作下旱作农田系统碳循环规律与碳汇机制研究

Conservation tillage with straw mulching and ridge planting as a mainstay is an important approach to control soil erosion, to improve soil fertility, to guard against seasonal drought and to increase crop productivity in purple hilly regions in southwest China. The research on rules of carbon cycle and mechanism of carbon sink in farmland ecosystems under conservation tillage is of important theoretical significance and practical values for responding to global climate changes, improving agro-ecological environment and promoting sustainable land productivity. In allusion to the fragile ecological environment and low production efficiency in purple hilly regions, and being aimed at enhancing the storage capacity of soil organic carbon in farmlands, this project emphasizes on the investigation of laws of soil carbon cycle and influencing factors of soil carbon dynamics in the dry-farming system under conservation tillage of straw mulching and ridge planting, the analysis of mechanism of soil carbon sink from the perspective of soil physical, chemical and microbiological processes, and the evaluation of potential of soil carbon sequestration under different agronomic management modes in both farmland and regional scale, so as to propose the adjustment measures of soil organic carbon in dry-farming systems. The results may lay a theoretical basis for the improvement of agro-ecological environment and the high and stable output in dry farmlands in purple hilly regions, and provide a decision-making basis for the governments in building a long-term mechanism of regional agricultural carbon sequestration and realizing the reduction of greenhouse gas emissions.

以秸秆覆盖、垄作为主体的保护性耕作是西南紫色土丘陵区控制水土流失、改善土壤肥力、抗御季节性干旱、提高作物生产力的重要途径。开展保护性耕作条件下农田生态系统碳循环规律与碳汇机制研究，对于应对全球气候变化、改善农业生态环境、增进土地可持续生产能力具有十分重要的理论意义和指导价值。本项目针对西南紫色土丘陵区生态环境脆弱和生产效益低下两大难题，以提高农田土壤有机碳库容量为主要目标，重点研究秸秆覆盖、垄作保护性耕作条件下旱作农田系统碳循环规律及土壤碳动态影响因素，阐明土壤物理过程、化学过程和微生物过程的土壤碳汇机制，从农田和区域尺度上明确不同农田管理模式下的土壤固碳潜力，进而提出旱作农田土壤有机碳调控途径，为该地区农业生态环境改善与旱作农业高产、稳产提供理论依据，为国家建立区域农业固碳长效机制和实现温室气体减排奠定决策基础。

针对西南紫色土丘陵区生态环境脆弱和生产效益低下两大难题，在研究不同保护性耕作模式生产效益基础上，重点研究不同耕作方式下旱作农田系统碳循环规律及其影响因素，从土壤物理、化学和微生物过程的角度探讨土壤碳汇机制，进而探明不同农田管理模式下的固碳潜力。结果表明：.①在旱三熟种植区，与传统耕作（T）相比，垄作（R）、传统耕作+秸秆覆盖（TS）、垄作+秸秆覆盖（RS）、传统耕作+秸秆覆盖+秸秆速腐剂（TSD）、垄作+秸秆覆盖+秸秆速腐剂（RSD）处理对土壤养分、水分和农田生态环境要素都有明显改善作用，可显著提高作物产量、效益和水分利用率，其中以RSD和RS综合效果最好。.②在“麦/玉/豆”旱三熟制下，R、TS、RS、TSD、RSD的年固碳总量比对照T分别增加11.29%、21.97%、19.68%、18.33和25.95%，以垄作和秸秆覆盖为主的保护性耕作能显著提高农田土壤-作物系统的碳汇能力，增汇幅度达9.93%~30.67%。.③农田土壤有机碳氮组分之间存在一定的耦合关系，总有机碳（TOC）与总氮（TN）、水溶性有机碳（DOC）与水溶性氮（DN）、微生物生物量碳（MBC）与微生物生物量氮（MBN）之间呈极显著正相关；活性有机碳（AOC）与TOC极显著正相关，说明土壤活性有机碳在一定程度上依赖于土壤总有机碳含量。.④垄作和秸秆覆盖可提高土壤微生物数量、酶活性、有机碳含量和作物生物量；可通过改良土壤理化性状，促进根系生长，提高根系活力，从而对土壤有机碳表现出截存效应；可促进作物生长发育，并增加作物干物质积累和碳氮储量，且以垄作+秸秆全量覆盖效果最佳。.⑤通过分析重庆市农田生态系统碳源/汇特征及固碳潜力，发现全市三大经济区域农田生态系统碳吸收、碳排放、碳汇的总量和强度依次为一小时经济圈>渝东北>渝东南；从农田土壤有机碳密度看，渝西南、渝东北和渝东南较高，长江干流沿岸及附近低山丘陵区较低；全市农田土壤固碳潜力约为30.82TgC，单位面积农田土壤固碳潜力平均为6.71t/hm2。.研究结果可为农田生态系统管理措施的优化和农业节能减排政策的制定提供科学指导。.