Abstract
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°CThis article is part of the theme issue ‘The role of soils in delivering Nature's Contributions to People’.
Highlights
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
Forests and woodlands store a disproportionate share of the global soil organic carbon (SOC) stock: they represent slightly less than 40% of global land area, but at approximately 400 Pg SOC, they store more than 45% of the SOC stock to 1 m [12,13,14]
Summary
The contribution of soils to the nature’s contribution to people (NCP) ‘Regulation of Climate’ is controlled by the emission and sequestration of greenhouse gases (GHGs), biogenic volatile organic compounds and aerosols, and through impacts on biophysical feedbacks (e.g. albedo, evapotranspiration). The amount and type (1 : 1 versus 2 : 1) of clay minerals are critical in relation to the formation of stable microaggregates that can encapsulate SOM, decrease its accessibility to microbes [76] and affect the future of SOC Another physical process of increasing MRT is the translocation of SOM from surface into the subsoil layers, and further away from the zone of intense agricultural and climatic perturbations. In nonflushing soils of dry climates, limestone is dissolved by carbonic acid (H2CO3) and produces Ca2+ and 2HCOÀ3 , which reprecipitate as pedogenic CaCO3 (figure 3) This reprecipitated CaCO3, does not sequester atmospheric C because the source of Ca2+ is from pre-existing CaCO3 and, the CO2 that was consumed in the reaction to form carbonic acid is released upon the reprecipitation of CaCO3 [52]. Judicious management of soils benefits adaptation to climate change by ‘producing more from less’, enhancing eco-efficiency and reducing losses by erosion and other degradation processes (figure 5)
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