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1. The Future of Soils in the Midwestern United States

   https://doi.org/10.1029/2022EF003104  

   Kwang, J S; Thaler, E A; Larsen, I J (May 2023, Earth's Future)

   Abstract Soil is the source of the vast majority of food consumed on Earth, and soils constitute the largest terrestrial carbon pool. Soil erosion associated with agriculture reduces crop productivity, and the redistribution of soil organic carbon (SOC) by erosion has potential to influence the global carbon cycle. Tillage strongly influences the erosion and redistribution of soil and SOC. However, tillage is rarely considered in predictions of soil erosion in the U.S.; hence regionwide estimates of both the current magnitude and future trends of soil redistribution by tillage are unknown. Here we use a landscape evolution model to forecast soil and SOC redistribution in the Midwestern United States over centennial timescales. We predict that present‐day rates of soil and SOC erosion are 1.1 ± 0.4 kg ⋅ m^−‐2 ⋅ yr^−‐1and 12 ± 4 g ⋅ m⁻² ⋅ yr⁻¹, respectively, but these rates will rapidly decelerate due to diffusive evolution of topography and the progressive depletion of SOC in eroding soil profiles. After 100 years, we forecast that 8.8 (+1.9/−2.1) Pg of soil and 0.17 (+0.03/−0.04) Pg of SOC will have eroded, causing the surface concentration of SOC to decrease by 4.4% (+0.9/−1.1%). Model simulations that include more widespread adoption of low‐intensity tillage (i.e., no‐till farming) determine that soil redistribution, SOC redistribution, and surficial SOC loss after 100 years would decrease by ∼95% if low‐intensity tillage is fully adopted. Our findings indicate that low‐intensity tillage could greatly decrease soil degradation and that the potential for agricultural soil erosion to influence the global carbon cycle will diminish with time due to a reduction in SOC burial. 

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2. Reduced Erosion Augments Soil Carbon Storage Under Cover Crops

   https://doi.org/10.1111/gcb.70133  

   Huang, Wenjuan; Jiang, Lifen; Zhou, Jian; Kim, Hyung‐Sub; Xiao, Jingfeng; Luo, Yiqi (March 2025, Global Change Biology)

   ABSTRACT Cover crops, a promising strategy to increase soil organic carbon (SOC) storage in croplands and mitigate climate change, have typically been shown to benefit soil carbon (C) storage from increased plant C inputs. However, input‐driven C benefits may be augmented by the reduction of C outputs induced by cover crops, a process that has been tested by individual studies but has not yet been synthesized. Here we quantified the impact of cover crops on organic C loss via soil erosion (SOC erosion) and revealed the geographical variability at the global scale. We analyzed the field data from 152 paired control and cover crop treatments from 57 published studies worldwide using meta‐analysis and machine learning. The meta‐analysis results showed that cover crops widely reduced SOC erosion by an average of 68% on an annual basis, while they increased SOC stock by 14% (0–15 cm). The absolute SOC erosion reduction ranged from 0 to 18.0 Mg C⁻¹ ha⁻¹ year⁻¹and showed no correlation with the SOC stock change that varied from −8.07 to 22.6 Mg C⁻¹ ha⁻¹ year⁻¹at 0–15 cm depth, indicating the latter more likely related to plant C inputs. The magnitude of SOC erosion reduction was dominantly determined by topographic slope. The global map generated by machine learning showed the relative effectiveness of SOC erosion reduction mainly occurred in temperate regions, including central Europe, central‐east China, and Southern South America. Our results highlight that cover crop‐induced erosion reduction can augment SOC stock to provide additive C benefits, especially in sloping and temperate croplands, for mitigating climate change. 

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3. How moisture availability Across climate zones, landscapes, and pedons governs soil organic C spatial heterogeneity and transport to deep horizons.

   Unruh, M. (December 2023, AGU abstract)

   Clarifying the mechanisms that control variability in the spatial distribution of soil organic carbon (SOC) is key to accurate estimates of soil C fluxes. Mobile organic C (MOC), here defined as the fraction of SOC that is not strongly bound to mineral surfaces but that can be transported hydrologically as dissolved or particulate organic C, represents the portion of SOC whose residence time can be modulated via movement down profiles and across landscapes. The relationship between the spatial arrangement and turnover time of SOC is especially evident in the widely observed correlation between soil depth and mean residence time; deeper SOC tends to persist for relatively long periods in the profile.  Moisture can promote microbial mineralization of SOC to CO2, but water also can transport MOC throughout profiles and landscapes. Controls on the movement of MOC have not been fully elucidated however, and the relationship between MOC and the spatial arrangement of SOC has not been thoroughly explored. Using data collected from five distinct ecosystem types across North America we evaluate the hypothesis that moisture dynamics throughout the soil profile as driven by seasonality, vegetation productivity, and topographical position influence the spatial distribution of MOC, and thus the observed heterogeneity of SOC and its persistence. We demonstrate that, in soils with surplus water availability and structural features that permit sufficient flow, transport drives the accumulation of disproportionately large concentrations of MOC deep in the profile and in downslope topographical positions. Our results further demonstrate that the vertical and lateral transport of MOC is also regulated by variation between energy- and water-limited systems in the amount of seasonally-available water moving through the profile: at times and in places where relatively more surplus water is available, MOC is more readily translocated. Excursions from these patterns of transport and accumulation result from soil textural and structural characteristics that immobilize organic C or inhibit flow. These findings reveal the nuances of how soil moisture dynamics regulate vertical and lateral distributions of MOC, thereby promoting the development of heterogeneous SOC stores as well as deep, relatively persistent SOC pools. 

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4. Post-fire SOC and delta-13C at different types of microsite at a grassland-shrubland ecotone

   https://doi.org/10.6073/pasta/993cd7029af115ee4508c2a688af7bf9  

   Wang, Guan (January 2018, Environmental Data Initiative)

   Woody plant encroachment of grassland ecosystems is a geographically extensive phenomenon that can lead to rapid land degradation and significantly alter global biogeochemical cycles, and this ecosystem change has been particularly well documented in the desert grassland of the southwestern United States. Fires are known to decrease vegetation cover and increase soil erodibility, and the shifts in wildfire regimes are currently occurring in Chihuahuan Desert. It is generally recognized that the invasion of woody vegetation into grasslands and savannas will increase the carbon stored in arid ecosystems. However, carbon storage may be complicated by disturbance such as wildfire, which alters the distribution and amount of C pools in the drylands. The relative distribution of each vegetation type to the soil C pool and its variability after fires are not well-understood in this ecosystem. This research will investigate the variations of SOC and its vegetation source partition at microsite scale in the woody shrub encroached grassland after the occurrence of fire, which will provide further information on wildfire’s influence on soil C pool dynamics in arid and semiarid lands. The post-fire changes of the spatial pattern of SOC and vegetation contributions in the shrub encroached grassland will be analyzed using a geostatistical method outlined in Guan et al. (2018). Overall, understanding the post-fire redistribution and sources of SOC may provide insights on the important role played by fire, aeolian processes and vegetation in the dynamics of desert grassland ecosystems. 

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5. The role of soil in regulation of climate

   https://doi.org/10.1098/rstb.2021.0084  

   Lal, Rattan; Monger, Curtis; Nave, Luke; Smith, Pete (September 2021, Philosophical Transactions of the Royal Society B: Biological Sciences)

   null (Ed.)

   The soil carbon (C) stock, comprising soil organic C (SOC) and soil inorganic C (SIC) and being the largest reservoir of the terrestrial biosphere, is a critical part of the global C cycle. Soil has been a source of greenhouse gases (GHGs) since the dawn of settled agriculture about 10 millenia ago. Soils of agricultural ecosystems are depleted of their SOC stocks and the magnitude of depletion is greater in those prone to accelerated erosion by water and wind and other degradation processes. Adoption of judicious land use and science-based management practices can lead to re-carbonization of depleted soils and make them a sink for atmospheric C. Soils in humid climates have potential to increase storage of SOC and those in arid and semiarid climates have potential to store both SOC and SIC. Payments to land managers for sequestration of C in soil, based on credible measurement of changes in soil C stocks at farm or landscape levels, are also important for promoting adoption of recommended land use and management practices. In conjunction with a rapid and aggressive reduction in GHG emissions across all sectors of the economy, sequestration of C in soil (and vegetation) can be an important negative emissions method for limiting global warming to 1.5 or 2°C This article is part of the theme issue ‘The role of soils in delivering Nature's Contributions to People’. 

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