Elias Dafydd M O, Mason Kelly E, Howell Katherine, Mitschunas Nadine, Hulmes Lucy, Hulmes Sarah, Lebron Inma, Pywell Richard F, McNamara Niall P
UK Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, LA1 4AP, United Kingdom.
UK Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster, LA1 4AP, United Kingdom.
J Environ Manage. 2023 May 15;334:117465. doi: 10.1016/j.jenvman.2023.117465. Epub 2023 Feb 11.
Grasslands account for ∼30% of global terrestrial carbon (C), of which most is stored in soils and provide important ecosystem services including livestock and forage production. Reseeding of temporary grasslands on a 5-year cycle is a common management practice to rejuvenate sward productivity and reduce soil compaction, but is physically disruptive and may reduce soil organic carbon (SOC) stocks. However, research to date is limited, which impacts on the ability to optimise grassland management for climate change mitigation. To determine whether extending the time interval up to 20 years between grassland reseeding can increase stable SOC stocks, a soil survey was conducted across three UK grassland chrono-sequences comprising 24 fields on contrasting soil types. We found that grassland SOC stocks (39.8-114.8 Mg C ha) were higher than co-located fields in arable rotations (29.3-83.2 Mg C ha) and the relationship with grassland age followed a curvilinear relationship with rapid SOC stock accumulation in the year following reseeding (2.69-18.3 Mg C ha yr) followed by progressively slower SOC accumulation up to 20 years. Contrary to expectation, all grasslands had similar soil bulk densities and sward composition questioning the need for traditional 5-year reseeding cycles. Fractionation of soils into stable mineral associated fractions revealed that coarse textured grassland topsoils (0-15 cm) were near-saturated in C irrespective of grassland age whilst loam soils reached saturation ∼10 years after reseeding. Fine-textured topsoils and subsoils (15-30 cm) of all textures were under saturated and thus appear to hold the most potential to accrue additional stable C. However, the lack of a relationship between C saturation deficit and grassland age in subsoils suggests that more innovative management to promote SOC redistribution to depth, such as a switch to diverse leys or full inversion tillage may be required to maximise subsoil SOC stocks. Taken together our findings suggest that extending the time between grassland reseeding could temporarily increase SOC stocks without compromising sward composition or soil structure. However, detailed monitoring of the trade-offs with grassland productivity are required. Fine textured soils and subsoils (15-30 cm) have the greatest potential to accrue additional stable C due to under saturation of fine mineral pools.
草原约占全球陆地碳（C）的30%，其中大部分碳储存在土壤中，并提供重要的生态系统服务，包括畜牧和草料生产。以5年为周期对临时草地进行重新播种是恢复草地生产力和减少土壤压实的常见管理措施，但这会对土壤造成物理干扰，可能会减少土壤有机碳（SOC）储量。然而，迄今为止的研究有限，这影响了为缓解气候变化而优化草地管理的能力。为了确定将草地重新播种的时间间隔延长至20年是否能增加稳定的SOC储量，我们对英国三个草地时间序列进行了土壤调查，这些序列包括24块不同土壤类型的田地。我们发现，草地的SOC储量（39.8 - 114.8 Mg C/ha）高于轮作耕地中同位置的田地（29.3 - 83.2 Mg C/ha），且与草地年龄的关系呈曲线关系，重新播种后的第一年SOC储量迅速积累（2.69 - 18.3 Mg C/ha·yr），之后直至20年SOC积累逐渐减缓。与预期相反，所有草地的土壤容重和草皮组成相似，这对传统的5年重新播种周期的必要性提出了质疑。将土壤分离为与稳定矿物相关的组分表明，无论草地年龄如何，质地较粗的草地表层土壤（0 - 15厘米）的碳含量接近饱和，而壤土在重新播种后约10年达到饱和。所有质地的细质地表层土壤和亚表层土壤（15 - 30厘米）的碳含量不饱和，因此似乎最有潜力积累额外的稳定碳。然而，亚表层土壤中碳饱和度亏缺与草地年龄之间缺乏相关性，这表明可能需要采取更具创新性的管理措施来促进SOC向深层重新分配，例如改用多样化轮作或全面翻耕，以最大限度地提高亚表层土壤的SOC储量。综合来看，我们的研究结果表明，延长草地重新播种的时间间隔可以暂时增加SOC储量，而不会影响草皮组成或土壤结构。然而，需要详细监测与草地生产力之间的权衡。由于细矿物库不饱和，细质地土壤和亚表层土壤（15 - 30厘米）积累额外稳定碳的潜力最大。
