Soil carbon change in intensive agriculture after 25 years of conservation management

• Published in: Geoderma 2025-01, Vol.453 (C), p.117133, Article 117133
• Main Authors: Córdova, S. Carolina, Kravchenko, Alexandra N., Miesel, Jessica R., Robertson, G. Philip
• Format: Article
• Language: English
• Subjects: Agriculture; Cover crops; Ecological succession; Forest soils; No-till; Pyrogenic carbon; Soil organic matter
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2024.117133

•We examined long-term soil carbon change in 10 replicated ecosystems over 25 years.•Whole profile soil carbon gain was greater in diverse perennial systems.•We found no evidence of subsurface carbon loss in no-till or other systems.•Soil carbon did not change in conventional row crops nor in late successional forest.•Pyrogenic carbon comprised ∼15 % of soil organic carbon to 50 cm depth in all systems and ∼ 40 % below that. 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 seques