长期保护性耕作对半干旱区黄绵土碳固存和碳排放的影响及机制

Soil C sequestration is a bridge across food security and climate change. Previous research showed that proper conservation tillage does not only conserve soil water and improve productivity; it can also sequestrate C and reduce C emission from soil. However, conservation tillage effects on Loess soil’s C sequestration and emission is unknown, and its underlining mechanisms remain a mystery. .In this context, on a long-term field experiment under different tillage practices (conventional tillage, no-tillage with stubble retention, no-tillage, conventional tillage with stubble incorporated) which commenced in 2001 in semiarid areas on the Loess Plateau, the integrated methods of field experiment, lab analysis and multivariate analysis will be used to analyze soil organic C and inorganic C of historical soil samples and fresh soil samples within this project and monitor CO2 emission from soil..This study integrates historical soil and crop data from the long-term experiment to explore (1) evolution of soil C sequestration responses to long-term different tillage practices, (2) quantify CO2 emission responses to long-term different tillage practices, and (3) determined physical, chemical and biological mechanisms of long-term conservation tillage practices effects on C sequestration and emission. The study aimed to ascertain the main mechanisms of long-term conservation tillage effects on C sequestration and CO2 emission of Loess soils in semiarid areas on the Loess Plateau, and thereby provides theoretical bases for the extension and adoption of conservation tillage in the research area and helps in decision-making on soil tillage and crop production under changing climate.

土壤碳固存是粮食安全和气候变化之间的桥梁和纽带。有研究表明适宜的保护性耕作技术不仅保持水土、提高产量，还可固碳减排。但保护性耕作对半干旱区黄绵土碳固存与排放的影响尚不清楚，机理更是未知。为此，本研究拟借助2001年在黄土高原半干旱区建立的不同耕作措施（传统耕作、免耕秸秆覆盖、免耕、传统耕作秸秆翻埋）长期定位试验，采用大田试验、室内分析、多元分析相结合的方法，通过对历年保存土样和本项目执行期土壤有机、无机碳的分析和CO2排放监测，结合历年作物、土壤方面的数据，研究（1）长期不同耕作措施下黄绵土碳固存的演变规律；（2）黄绵土碳排放对耕作措施的响应特征；（3）不同耕作措施影响黄绵土碳固存与排放的的土壤物理保护机制、土壤化学机制和土壤生物学机制。以期明确长期保护性耕作措施对半干旱区黄绵土碳固存和碳排放的影响及其主要机制，为该区保护性耕作的推广应用和气候变化背景下土壤耕作和作物生产决策提供理论依据。

土壤是地球最大的陆地C库，增加土壤碳固存、扩大土壤碳库，减少土壤CO2排放不仅可以缓和当前大气CO2浓度的不断增加，也可以提高土壤质量、提高土壤的抗蚀能力、生产力水平及生态系统服务功能，改善生活环境。因此，在全球尺度上，土壤碳固存是联系粮食安全和气候变化的纽带和桥梁。保护性耕作通过改变影响土壤碳固存与排放的土壤物理性质、化学性质和生物学性质作用于土壤碳库，固碳减排。本研究拟依托课题组于2001年起在黄土高原西部半干旱雨养农业区建立的不同耕作措施的长期定位试验，研究了半干旱区黄绵土碳固存对长期不同耕作措施的响应及其随时间的演变动态、黄土高原半干旱区黄绵土碳排放对长期不同耕作措施的响应特征，探讨了长期保护性耕作对半干旱区黄绵土碳固存与碳排放的影响及机制。研究表明，在陇中黄土高原半干旱雨养农业区，采取免耕秸秆覆盖的保护性耕作措施能够改良土壤物理性状、增加作物产量，增加土壤碳固存，减少碳排放。与传统耕作相比较，作物碳固存增加24-27%，作物生长季土壤碳排放量减少21-33%，提高碳排放效率也显著提高，是该区实现作物增产、土壤碳增汇减排的最合理的耕作措施。