• Energy Research

Soil carbon sequestration (enhanced sinks) is the mechanism responsible for most of the greenhouse gas (GHG) mitigation potential in the agriculture sector. Carbon sequestration in grasslands can be determined directly by measuring changes in soil organic carbon (SOC) stocks and indirectly by measuring the net balance of C fluxes. A literature search shows that grassland C sequestration reaches on average 5 ± 30 g C/m2 per year according to inventories of SOC stocks and -231 and 77 g C/m2 per year for drained organic and mineral soils, respectively, according to C flux balance. Off-site C sequestration occurs whenever more manure C is produced by than returned to a grassland plot. The sum of on- and off-site C sequestration reaches 129, 98 and 71 g C/m2 per year for grazed, cut and mixed European grasslands on mineral soils, respectively, however with high uncertainty. A range of management practices reduce C losses and increase C sequestration: (i) avoiding soil tillage and the conversion of grasslands to arable use, (ii) moderately intensifying nutrient-poor permanent grasslands, (iii) using light grazing instead of heavy grazing, (iv) increasing the duration of grass leys; (v) converting grass leys to grass-legume mixtures or to permanent grasslands. With nine European sites, direct emissions of N2O from soil and of CH4 from enteric fermentation at grazing, expressed in CO2 equivalents, compensated 10% and 34% of the on-site grassland C sequestration, respectively. Digestion inside the barn of the harvested herbage leads to further emissions of CH4 and N2O by the production systems, which were estimated at 130 g CO2 equivalents/m2 per year. The net balance of on- and off-site C sequestration, CH4 and N2O emissions reached 38 g CO2 equivalents/m2 per year, indicating a non-significant net sink activity. This net balance was, however, negative for intensively managed cut sites indicating a source to the atmosphere. In conclusion, this review confirms that grassland C sequestration has a strong potential to partly mitigate the GHG balance of ruminant production systems. However, as soil C sequestration is both reversible and vulnerable to disturbance, biodiversity loss and climate change, CH4 and N2O emissions from the livestock sector need to be reduced and current SOC stocks preserved.

AbstractAmazonian forests continuously accumulate carbon (C) in biomass and in soil, representing a carbon sink of 0.42–0.65 GtC yr−1. In recent decades, more than 15% of Amazonian forests have been converted into pastures, resulting in net C emissions (~200 tC ha−1) due to biomass burning and litter mineralization in the first years after deforestation. However, little is known about the capacity of tropical pastures to restore a C sink. Our study shows in French Amazonia that the C storage observed in native forest can be partly restored in old (≥24 year) tropical pastures managed with a low stocking rate (±1 LSU ha−1) and without the use of fire since their establishment. A unique combination of a large chronosequence study and eddy covariance measurements showed that pastures stored between −1.27 ± 0.37 and −5.31 ± 2.08 tC ha−1 yr−1while the nearby native forest stored −3.31 ± 0.44 tC ha−1 yr−1. This carbon is mainly sequestered in the humus of deep soil layers (20–100 cm), whereas no C storage was observed in the 0‐ to 20‐cm layer. C storage in C4 tropical pasture is associated with the installation and development of C3 species, which increase either the input of N to the ecosystem or the C:N ratio of soil organic matter. Efforts to curb deforestation remain an obvious priority to preserve forest C stocks and biodiversity. However, our results show that if sustainable management is applied in tropical pastures coming from deforestation (avoiding fires and overgrazing, using a grazing rotation plan and a mixture of C3 and C4 species), they can ensure a continuous C storage, thereby adding to the current C sink of Amazonian forests.

The Paris Climate Agreements and Sustainable Development Goals, signed by 197 countries, present agendas and address key issues for implementing multi-scale responses for sustainable development under climate change—an effort that must involve local, regional, national, and supra-national stakeholders. In that regard, Continental Carbon Sequestration (CoCS) and conservation of carbon sinks are recognized increasingly as having potentially important roles in mitigating climate change and adapting to it. Making that potential a reality will require indicators of success for various stakeholders from multidisciplinary backgrounds, plus promotion of long-term implementation of strategic action towards civil society (e.g., law and policy makers, economists, and farmers). To help meet those challenges, this discussion paper summarizes the state of the art and uncertainties regarding CoCS, taking an interdisciplinary, holistic approach toward understanding these complex issues. The first part of the paper discusses the carbon cycle’s bio-geophysical processes, while the second introduces the plurality of geographical scales to be addressed when dealing with landscape management for CoCS. The third part addresses systemic viability, vulnerability, and resilience in CoCS practices, before concluding with the need to develop inter-disciplinarity in sustainable science, participative research, and the societal implications of sustainable CoCS actions.

In Benin, adaptation to climate change in the livestock sector has led cattle farmers to develop different livestock practices. Most research has focused on evaluating the effects of these practices on livestock productivity. However, information on the effect of these practices on carbon (C) sequestration in farmland soils is lacking. Soil C sequestration has been identified as a potential strategy to offset greenhouse gas emissions. Thus, the present study aimed at filling this gap. The calculation was one hand based on inventory data obtained from literature sources (excrement production of each cattle category, moisture content of each crop, ratio of crop residue to main product, and C content of the main product and excrement) and on the other hand on activity data (cattle herd size, manure applied, land use area, crop yield, and crop residues management) obtained from surveys carried out among 360 cattle farmers belonging to 3 cattle farming types. The results revealed that whatever the cattle farming type, annual C input from manure was higher (p˂0.05) than C input from crop residues. Annual C sequestration in farmland soil of farms integrating livestock with cereal-legume and forage crops was significantly higher (Type 2: 158.07 ± 1.79 kg C ha-1 year-1) followed by farms integrating livestock with cereal-legume crops (Type 1: 99.51 ± 0.95 kg C ha-1 year-1), which in turn had a higher value than farms practicing pastoral mobility (Type 3: 78.46 ± 0.70 kg C ha-1 year-1). These results highlight the potential for climate change mitigation through these farming practices. This is justified because the quantity of C sequestered in farmland soil of all cattle farming types was significant. Thus, for future research, it is necessary to include soil C sequestration in the calculations of farms' carbon footprint.

DATA4C+ is a thesaurus classifying and defining land management practices in agriculture and forestry for soil carbon storage. DATA4C+ thesaurus is focussed on land management practices identified in the scientific literature as drivers of soil organic carbon (SOC) changes. DATA4C+ thesaurus aim was to fill the gap of lack of a comprehensive thesaurus for land management practices which directly or indirectly affect SOC dynamics.