15年保护性耕作对黄土坡耕地区土壤及团聚体固碳效应的影响

【目的】保护性耕作是提高土壤有机碳（SOC）含量、促进土壤团聚体形成的重要措施。论文旨在揭示保护性耕作对土壤表层（0-10 cm）有机碳含量及储量的影响，探讨不同级别团聚体的固碳特征，为阐明土壤固碳机理和筛选黄土坡耕地区农田土壤增碳耕作措施提供理论依据。【方法】长期试验位于黄土高原坡耕地区，开始于1999年，共设4个处理：少耕（RT）、免耕覆盖（NT）、深松覆盖（SM）和传统翻耕（CT）。利用15年长期试验的作物产量和0-10 cm 土层土壤有机碳数据分析农田碳投入和土壤固碳量；通过湿筛法筛分＞2、1-2、0.25-1、0.053-0.25和＜0.053 mm粒级团聚体，分析不同团聚体的固碳特征。【结果】15年长期免耕覆盖和深松覆盖处理显著提高了土壤0-10 cm表层有机碳含量及储量，同传统翻耕处理相比，有机碳含量分别提高了22.9%和21.8%，有机碳储量分别提高了21.8%和16.7%，固碳速率分别为0.09和0.06 t C?hm^-2?a^-1。微团聚体（＜0.25 mm）存储了大部分的有机碳，占总团聚体有机碳储量的65%，但其有机碳含量较低。大团聚体（＞0.25 mm）有机碳含量较高，约为微团聚体的3-8倍，且对不同耕作措施反应敏感，可作为评价长期不同耕作措施对土壤有机碳含量影响的指标。土壤固碳量随着累积碳投入量的增加而显著增加，要维持土壤有机碳储量稳定，每年最低需投入外源碳2.4 t C?hm^-2。【结论】长期保护性耕作（包括免耕覆盖和深松覆盖）提高了黄土坡耕地区土壤及团聚体有机碳储量，是有利于该地区土壤增碳的管理措施。

Effects of 15-Year Conservation Tillage on Soil and Aggregate Organic Carbon Sequestration in the Loess Hilly Region of China

【Objective】Conservation tillage is an essential measure as its function in improving the soil organic carbon (SOC) contents and the stabilization of soil aggregation. The objectives of this study are to (i) reveal the SOC sequestration under 15-year tillage systems and (ii) evaluate the contributions of different sizes of aggregates on carbon sequestration in the Loess Hilly region of China. 【Method】A long-term tillage experiment, started in 1999, was used for the study. The tillage treatments included: reduced tillage (RT), no-tillage (NT), sub-soiling with mulch (SM), and conventional tillage (CT). Recorded winter wheat yields and SOC contents at depths of 0-10 cm during the 15 years were used to estimate C input and SOC stocks, and soil samples collected in 2013 were separated into＞2, 1-2, 0.25-1, 0.053-0.25, and＜0.053 mm using a wet sieving method and the content of organic carbon in these aggregates were analyzed. 【Result】SOC stocks in the 0-10 cm soil layer of NT and SM were 10.9 and 10.6 t C?hm^-2, and were significantly larger than RT and NT. SOC sequestration rates of NT and SM were 0.09 and 0.06 t C?hm^-2?a^-1. Microaggregate stored most of the organic carbon, accounting for 65% of the total organic carbon stock of the aggregate, implying that microaggregate plays an important role in SOC stock. But the organic carbon contents of microaggregates were not sensitive to tillage, indicating a C saturation in the microaggregate. Macroaggregates had higher organic carbon contents, which were about 3-8 times that of the microaggregates, and the organic carbon contents of macroaggregates were sensitive to tillage. Organic carbon stocks of macroaggregate responded positively to cumulative C input, and that means macroaggregates had a high carbon sequestration potential. SOC sequestration significantly increased with the increase of cumulative carbon inputs. To maintain the soil organic carbon stock at a stable level, the minimum annual need for C input amount was 2.4 t C?hm^-2. 【Conclusion】The long-term conservation tillage (included no-tillage and sub-soiling and mulch management), is a sustainable soil carbon enhancement method for these dryland soils for the Loess Hilly region of China, it significantly promoted C sequestration and the newly organic C was mainly accumulated in the macroaggregates.