关键词: 团聚体, 有机碳, δ¹³C, 土壤酶, 添加秸秆, 耕作措施

Abstract:

【Objective】Straw addition is an effective means to increase soil organic carbon, which is significant to ensure the sustainability of the organic carbon in the farmland system. This study aimed at investigating the effect of straw addition on soil organic carbon (SOC) and related factors under different tillage treatments, so as to provide a theoretical basis for the management of carbon sequestration and yield increase in northern dry farmland. 【Method】The field soil samples from long-term conventional tillage (CT) and no-tillage (NT) for in-lab incubation experiment were collected. Four treatments were set up, namely, conventional tillage soil without straw (CT), no tillage soil without straw (NT), conventional tillage soil with straw (CTS), and no-till soil with straw (NTS), respectively. Each treatment owned 15 repetitions. The incubation experiment was conducted in a constant temperature incubator at 25 ℃ for 180 days, and the soil samples were periodically taken to determine the content of SOC, aggregate composition, microbial biomass carbon and the activity of related enzymes. 【Result】(1) Straw addition significantly increased the content of soil organic carbon and large aggregates. Compared with CT, CTS increased SOC by 15%-46%; compared with NT, NTS increased SOC 12%-21%; compared to the initial organic carbon content, at the end of cultivation, CTS and NTS increased by 26.8% and 7.0%, respectively. CTS and NTS had the highest particle size of 2 000-250 μm, accounting for 41%-50% of all aggregates. Compared with CT, CTS increased the proportion of aggregates >250 μm by 235%-310%, and NTS increased the proportion of aggregates >250 μm by 96%-149%. (2) The addition of straw significantly increased the δ¹³C value of soil organic carbon. The CTS treatment was 80.93‰-115.22‰, NTS was 48.92‰-80.49‰; CTS straw-derived carbon was significantly higher than NTS by 13%-66%. (3) The addition of straw significantly increased the microbial biomass carbon (MBC) content, β-glucosidase (BG), β-cellobiosidase (CBH) and β-xylosidase (BXYL) activities. Compared with CT, CTS increased MBC content by 239%-623%, and increased BG, CBH and BXYL activity by 58%-170%, 52%-337% and 117%-170%, respectively; compared to NT, NTS increased MBC content by 124%-555%, and increased BG, CBH and BXYL activities by 28%-181%, 4%-304% and 13%-118%. (4) Soil organic carbon was significantly positively correlated with BG, CBH, BXYL activity, MBC and the proportion of >2 000 μm, 2 000-250 μm aggregates, and negatively correlated with the proportion of 250-53 μm and ＜53 μm aggregates. The activities of BG, CBH and BXYL showed a very significant positive correlation with each other, and were significantly positively correlated with MBC, >2 000 μm aggregates, 2 000-250 μm aggregates, and extremely negative with ＜53 μm aggregates. Linear correlation analysis results showed that water-stable macroaggregates (>250 μm) could explain 48% of organic carbon changes, MBC could explain 45% of organic carbon changes, and BG, CBH and BXYL enzyme activities could explain 66%, 44% and 53% of organic carbon changes, respectively. 【Conclusion】The addition of straw could significantly increase the content of soil organic carbon and macroaggregates, increase the number of microorganisms, and promote the soil enzyme activity. The impact on soil organic carbon and its related factors was greater in conventional tillage soils. In addition to the physical protection of aggregates, the sequestration of straw carbon in soil also depended on the role of microorganisms in the soil.

Key words: aggregate, soil organic carbon, δ¹³C, soil enzyme, straw addition, tillage practices