长期施氮耦合短期玉米间作豆科作物对土壤团聚体组成及碳氮分布的影响

Effects of long-term different nitrogen application rates coupled with short-term maize-legume cover crop intercropping on soil aggregate composition and carbon-nitrogen distribution

  • 摘要: 华北平原土地复种指数高、种植结构单一、不具备休耕条件以及农业生产中长期“重用轻养”, 导致土壤生物多样性降低、养分转化受阻、有机碳和全氮含量降低、土壤结构变差等一系列耕层土壤退化问题。本研究依托中国科学院栾城农业生态系统试验站始于2003年的小麦-玉米轮作肥料定位试验, 2022年玉米季通过裂区区组开展了玉米单作和玉米-大豆(牧草绿肥兼用品种‘汾豆牧绿2号’)间作的对比试验, 研究长期不同施氮量下玉米间作豆科作物对土壤团聚体组成及其稳定性、有机碳和全氮在团聚体中分布的影响, 阐释间作体系中种间互作、根土互作对土壤碳氮物理保护作用的影响, 为发展“用养结合”的绿色种植技术提供参考。肥料试验设6个施氮水平, 每年施纯N量为0 (N0)、100 (N100)、200 (N200)、300 (N300)、400 (N400)和600 kg∙hm−2 (N600)。2024年9月玉米灌浆期采集作物根际土和非根际土, 分析其团聚体组成及有机碳和全氮含量。研究结果表明, 施肥对团聚体组成及其稳定性的影响弱于种植方式, 施肥只引起间作玉米(FM)粒级≥2 mm的粗大团聚体破碎率和稳定率产生显著变化, 大豆根际土(F)、单作玉米根际土(M)和非根际土(B)的团聚体稳定性在不同施肥处理间均无显著差异; 各施肥处理下, 与非根际土相比, 根际土粒级≥2 mm粗大团聚体破碎率降低、稳定率提高; 间作降低了玉米根际土的粗大团聚体破碎率, 以N400施肥处理下FM的粗大团聚体稳定率最高(39.3%)。表明适宜施氮有利于提高间作体系土壤团聚体稳定性。施氮可有效提升土壤有机碳和全氮含量, 但随施肥量的增加间作和单作土壤氮素提升幅度存在差异, 间作更有利于提升低氮处理土壤碳氮素含量。有机碳和全氮在大团聚体中的含量高于微团聚体和粉黏粒, 其中粒级0.25~2 mm的细大团聚体是土壤碳氮的主要贡献者, 其对土壤有机碳和全氮的贡献率分别为54.8%~77.0%和60.6%~69.3%。间作提高了大团聚体碳氮含量, 特别是对粗大团聚体碳氮影响最为显著, 说明种植方式的改变首先影响的是碳氮在大团聚体中的分布。由此可见, 玉米与豆科作物间作提高了土壤大团聚体含量, 增加了土壤团聚体稳定性及有机碳和全氮含量, 有利于促进土壤碳氮固持。

     

    Abstract: The North China Plain faces a series of topsoil degradation issues—including reduced soil biodiversity, impeded nutrient transformation, decreased organic carbon and nitrogen content, and deteriorated soil structure—due to high multiple cropping index, monoculture cropping, lack of fallow periods, and long-term emphasis on production over conservation in agricultural practices. Based on a long-term fertilization experiment initiated in 2003 in a wheat–maize rotation system at the Luancheng Agro-Ecosystem Experimental Station, Chinese Academy of Sciences, a split-plot design was implemented during the 2022 maize season to compare monoculture maize with maize intercropped with a legume (Fendou Mulv No. 2, a forage-green manure variety). This study investigated the effects of long-term nitrogen (N) application rates combined with legume intercropping on soil aggregate composition, stability, and the distribution of organic carbon (SOC) and total nitrogen (TN) within aggregates. The aim was to clarify how interspecific and root–soil interactions in the intercropping system contribute to the physical protection of soil carbon and nitrogen, thereby supporting the development of green technologies that integrate land use with soil conservation. The experiment included six N application levels: 0 (N0), 100 (N100), 200 (N200), 300 (N300), 400 (N400), and 600 kg N ha-1 (N600). During the maize grain-filling stage in September 2024, rhizosphere and non-rhizosphere soil samples were collected to analyze aggregate composition, SOC, and TN content. The results showed that fertilization had a weaker influence on aggregate composition and stability than cropping patterns. Significant changes in fragmentation and stability rates of coarse macroaggregates (≥2 mm) were observed only in the rhizosphere of intercropped maize (FM). No significant differences were detected across N treatments in the rhizosphere of the legume (F), monocropped maize (M), or bulk soil (B). Across all N levels, the rhizosphere soils (FM, F, M) showed reduced fragmentation and increased stability of coarse macroaggregates (≥2 mm) compared to non-rhizosphere soil. Intercropping reduced the fragmentation rate and increased the content of water-stable macroaggregates in the maize rhizosphere, with the highest stability (39.3%) occurring under the N400 treatment, indicating that appropriate N application improves aggregate stability in intercropping systems. Nitrogen application enhanced SOC and TN content, but the extent of increase differed between intercropping and monoculture under high N inputs. Intercropping was more beneficial for increasing soil carbon and nitrogen under low-N conditions. SOC and TN were mainly stored in macroaggregates, particularly in fine macroaggregates (0.25–2 mm), which contributed 54.8%–77.0% of SOC and 60.6%–69.3% of TN. Intercropping increased SOC and TN content within macroaggregates, most notably in coarse macroaggregates, suggesting that changes in cropping practice first affect the distribution of carbon and nitrogen in larger aggregates. In conclusion, maize-legume intercropping enhances the content and stability of macroaggregates, increases SOC and TN sequestration, and promotes the physical protection of soil organic matter.

     

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