添加玉米秸秆对旱作土壤团聚体及其有机碳含量的影响

【目的】研究玉米秸秆还田对不同耕作处理下旱地土壤团聚体及其有机碳的影响,旨在探究长期传统耕作土壤添加秸秆后团聚体及其有机碳的变化规律,并确定添加秸秆提高土壤有机碳的主要原因,为旱地农田固碳技术提供理论依据。【方法】采集大田长期试验地的传统耕作和免耕小区土样进行室内培养试验,设置4个处理,分别为传统耕作土壤不加秸秆（CT）、免耕土壤不加秸秆（NT）、传统耕作土壤加秸秆（CTS）和免耕土壤加秸秆（NTS）,15次重复;秸秆为传统耕作玉米植株地上部分,用量为5%烘干土质量,在25℃恒温培养箱中通气培养180 d,定期取样进行团聚体组成和有机碳含量的测定。【结果】（1）不加秸秆处理团聚体以250—53 μm为主,占全部团聚体的52%—66%;添加秸秆处理以2 000—250 μm团聚体为主,占全部团聚体的41%—50%,CTS较CT提高230%—302%,NTS较NT提高92%—134%。（2）添加秸秆处理平均重量直径（MWD）、几何平均直径（GMD）以及>0.25 mm团聚体百分比（R_0.25）显著提高,培养到180 d时,CTS较CT分别提高133%、130%和235%,NTS较NT分别提高53%、75%和87%。（3）培养至180 d时,CTS较CT分别提高250—53 μm和<53 μm团聚体有机碳70%和54%;NTS较NT分别提高250—53 μm和<53 μm团聚体有机碳30%和25%。（4）添加秸秆显著提高2 000—250 μm团聚体有机碳对土壤有机碳的贡献率,CTS和NTS分别为49%—61%和50%—60%,且受团聚体组成影响较大。【结论】添加秸秆能够有效提高旱作土壤大团聚体（>250 μm）形成并增强其稳定性,提高大团聚体有机碳对土壤有机碳的贡献率,且对传统耕作处理土壤的促进效果更明显。

Effect of Straw Addition on the Formation of Aggregates and Accumulation of Organic Carbon in Dryland Soil

【Objective】To understand the regularity of aggregation and organic carbon changes after adding straw in long-term conventional tillage soil and to explore the main reason of improved soil organic carbon, the effects of straw incorporation on soil aggregates and the organic carbon content in aggregate were determined, so as to provide theoretical basis for carbon fixation in dryland agriculture.【Method】 An in-lab incubation experiment was conducted for 180 days in a constant temperature incubator at 25℃ with the soil collected from conventional tillage and no-tillage field plot. Four treatments were set up, namely conventional soil without straw (CT), no-tillage soil without straw (NT), conventional tillage soil with straw (CTS) and no-till soil with straw (NTS). Each treatment was sampled 15 replicates periodically for aggregate and organic carbon determinations. The straw was the aboveground parts of maize collected from conventional tillage, and the dosage was 5% dry soil weight.【Result】 (1) Aggregate in CT and NT were dominated by 250-53 μm fraction, accounting for 52%-66% of total aggregates, while in CTS and NTS, the aggregates were dominated by 2 000-250 μm fraction, accounting for 41%-50% of total aggregates. CTS and NTS improved 2 000-250 μm aggregate by 230%-302% and 92%-134% relative to CT and NT, respectively. (2) Straw incorporation significantly increased the mean weight diameter (MWD), geometric mean diameter (GMD) and macro-aggregate content (R_0.25) of water-table aggregates. In the 180th day, CTS increased 133%, 130%, and 235%, respectively; compared with CT, NTS increased 53%, 75% and 87%, respectively, compared with NT. (3) In the 180th day, compared with CT, CTS increased the organic carbon content in aggregate of 250-53 μm and <53 μm by 70% and 54%, respectively, and compared with NT, NTS increased in the same aggregates by 30% and 25%, respectively. (4) The contribution of organic carbon in 2 000-250 μm aggregate to soil organic carbon was significantly increased by CTS and NTS, with improvement of 49%-61% and 50%-60%, respectively, which was more affected by aggregate composition. 【Conclusion】 The addition of straw could effectively increase the content of macroaggregates (>250 μm) in the dryland, enhance its stability and increase the contribution of macroaggregates to soil organic carbon, and had a greater effect on the conventional tillage soil.