Changes in soil organic carbon (SOC) and nitrogen (SON) are strongly affected by land management but few long-term comparative studies have surveyed changes throughout the whole soil profile. We quantified 25-year SOC and SON changes to 1 m in 10 replicate ecosystems at an Upper Midwest, USA site. We compared four annual cropping systems in maize (Zea mays)-soybean (Glycine max)-winter wheat (Triticum aestivum) rotations, each managed differently (Conventional, No-till, Reduced input, and Biologically based); in three managed perennial systems (hybrid Poplar (Populus × euramericana), Alfalfa (Medicago sativa), and Conifer (Pinus spp.); and in three successional systems (Early, Mid- and Late succession undergoing a gradual change in species composition and structure over time). Both Reduced input and Biologically based systems included winter cover crops. Neither SOC nor SON changed significantly in the Conventional or Late successional systems over 25 years. All other systems gained SOC and SON to different degrees. SOC accrual was fastest in the Early successional system (0.8 ± 0.1 Mg C ha−1 y−1) followed by Alfalfa and Conifer (avg. 0.7 ± 0.1 Mg C ha−1 y−1), Poplar, Reduced input, and Biologically based systems (avg. 0.4 ± 0.1 Mg C ha−1 y−1), and Mid-successional and No-till systems (0.3 and 0.2 Mg C ha−1 y−1, respectively). Over the most recent 12 years, rates of SOC accrual slowed in all systems except Reduced input and Mid-successional. There was no evidence of SOC loss at depth in any system, including No-till. Rates of SON accrual ranged from 64.7 to 0.8 kg N ha−1 y−1 in the order Alfalfa ≥ Early successional > Reduced input and Biologically based ≥ Poplar > No-till and Conifer > Mid-successional systems. Pyrogenic C levels in the Conventional, Early, and Late successional systems were similar despite 17 years of annual burning in the Early successional system (∼ 15 % of SOC to 50 cm, on average, and ∼40 % of SOC from 50 to 100 cm). Results underscore the importance of cover crops, perennial crops, and no-till options for sequestering whole profile C in intensively managed croplands.

中文翻译：

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25 年保护管理后集约化农业土壤碳变化


土壤有机碳 （SOC） 和氮 （SON） 的变化受土地管理的强烈影响，但很少有长期比较研究调查整个土壤剖面的变化。我们在美国上中西部的一个站点量化了 25 年 SOC 和 SON 的变化，即 10 个复制生态系统中的 1 米。我们比较了玉米 （Zea mays）-大豆 （Glycine max）-冬小麦 （Triticum aestivum） 轮作的四种一年生种植系统，每种系统的管理方式不同（常规、免耕、减少投入和基于生物）;在三个管理的多年生系统中（杂交杨 （Populus × euramericana）、紫花苜蓿 （Medicago sativa） 和针叶树 （Pinus spp.）;在三个演替系统中（早期、中期和晚期演替随着时间的推移，物种组成和结构逐渐发生变化）。减投和生物系统都包括冬季覆盖作物。在 25 年的时间里，SOC 和 SON 在常规或晚期演替系统中均未发生显著变化。所有其他系统都在不同程度上获得了 SOC 和 SON。早期演替系统（0.8 ± 0.1 Mg C ha-1 y-1）的SOC积累最快，其次是紫花苜蓿和针叶树（平均0.7 ± 0.1 Mg C ha-1 y-1）、杨树、减少投入和生物系统（平均0.4 ± 0.1 Mg C ha-1 y-1），以及中期演替和免耕系统（分别为0.3和0.2 Mg C ha-1 y-1）。在最近的 12 年中，除减少投入和中期演替外，所有系统的 SOC 应计率均有所放缓。没有证据表明任何系统（包括免耕系统）的深度 SOC 损失。SON 的累积率范围为 64.7 至 0.8 kg N ha-1 y-1 顺序为紫花苜蓿 ≥ 早期演替 > 投入减少和基于生物学≥杨 > 免耕和针叶树 > 中期演替系统。 尽管早期演替系统每年燃烧 17 年（平均 15 % 的 SOC 到 50 厘米，和 ∼ 40 的 SOC 从 50 到 100 厘米），但常规、早期和晚期演替系统中的产热 C 水平相似。结果强调了覆盖作物、多年生作物和免耕选择对于在集约化管理农田中封存整个剖面 C 的重要性。