Grow cover crops
System: Arable crops
Mainly applicable for: Cover crops can be established in various intercropping periods, with species selected according to objectives, crop rotation, soil, and climate.
Not applicable or effective for: More difficult to apply for short intercropping periods.
Description
Cover crops are plants grown during the fallow period between two main (cash) arable crops. They may be sown as single species or as multi-species mixtures, including legumes (which fix atmospheric nitrogen), non-legumes such as grasses or broadleaf species, or combinations of both. The choice of species, establishment methods, and management and termination strategies depend on local conditions and the farmer’s objectives. Cover crops should be sown early to maximise biomass without hindering the next crop. They can be managed on-site, by incorporation into the soil or as surface mulch, or harvested and utilized off-site, for example as forage or for bioenergy production.
Cover crops are widely used to increase soil organic matter and favour carbon storage on the long term, protect and improve soil health (as cover crops), and capture soil inorganic nitrogen after harvest (as catch crops), thereby reducing erosion, enhancing soil structure, and limiting nitrogen leaching.
Effects of bio-energy cover crops are not covered in this factsheet.
Mechanism of effect
Compared with bare soil, cover crops are primarily valued for their positive effects on soil carbon storage. By producing additional biomass both above- and below-ground, they supply additional organic matter, thereby enhancing soil organic carbon (SOC) stocks. In addition, cover crops improve soil structure and contribute to long-term soil fertility. Most SOC changes occur in the topsoil, where residues accumulate (0-15cm topsoil).
Their effects on GHG emissions are more variable. Cover crops can reduce indirect N₂O emissions by limiting nitrogen leaching, but direct N₂O emissions may increase depending on biomass quantity, C/N ratio, and anaerobic conditions. Fertilization practices can also play a role in GHG emissions (see explanation of variable effect). Also, there is a small increase in CO₂ emissions linked to fuel use for sowing and termination of the cover crop, but in most cases a reduction in CO2 from fertilizer inputs. Because N₂O emissions are highly sensitive to factors such as biomass production, C/N ratio, soil type, climate, and fertilization practices, the overall GHG emissions linked to cover crops can highly vary and are therefore difficult to assess. In most cases, the net effect is positive, but it ultimately depends on the balance between SOC sequestration and GHG emissions, mainly N₂O.
Compared with bare soil, cover crops also modify the surface energy balance, specifically by increasing the surface albedo (the share of sunlight reflected) and influencing thermal infrared radiation (linked to surface temperature). These biogeophysical effects can provide an additional cooling effect comparable in magnitude to carbon storage.
Reference situation
No cover crop (bare soil)
Legend
| ● – Small effect (<5%) | o – No effect | o – no effect |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | N/A – unknown effect |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) |
Effect on total greenhouse gas (GHG) emissions (kg CO2-eq)
| per ha | Level of evidence | |||
| Mean | min-max | |||
| Cover crops (all types) | ? | ●● – ●● | High | |
Effect per emission source
| Soil | Inputs | Energy use | ||||
| N2O | min-max | CO2 | min-max | CO2 | min-max | |
| Cover crops (all types) | ● | ●● – ● | ● | o – ● | ● | ● – ● |
Effect on soil organic carbon (SOC) stocks
| Relative change (%) in SOC%: | ||||
| Mean | (min-max) | Level of evidence | ||
| Cover crops (all types) | ● ● | ● – ●●● | High | |
| ● – small increase (<10%) | ● – small decrease (<5%) | o – no effect |
| ●● – medium increase (10-25%) | ●●– large decrease (≥5%) | ? – unknown effect |
| ●●● – large increase (>25%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) |
Explanation of variable effect
Cover crops (all types)
- GHG emissions: N₂O emissions differ widely among systems because they are shaped by the type of cover crop, the amount of biomass left to decompose, and the biochemical properties of that biomass (particularly its C/N ratio and degradability). These factors determine how quickly nitrogen is released and how easily microbes produce N₂O. Soil moisture, temperature, and residue management interact with these effects, creating further variability. Fertilization practices add another layer: reducing mineral fertilizer use thanks to nitrogen supplied by a cover crop can lower overall emissions, but fertilizing the cover crop itself, if excessive or poorly timed, can raise N₂O emissions.
- Soil organic carbon (SOC): Cover crops influence SOC in various ways because they alter both carbon inputs to the soil and the biological processes that control carbon losses, and carbon inputs and decomposition rates differ across systems. The effects depend strongly on the amount and quality of biomass they produce, how that biomass is managed, and the soil–climate conditions in which they are grown. This influences how much carbon the cover crop adds to the soil, whether residues are exported or retained, and how fast they break down. Grasses and high-biomass, high-C/N cover crops tend to build more SOC than legumes or low-biomass species. Climate and soil properties strongly influence decomposition rates. Cooler climates or soils rich in clay favor carbon retention, while warm conditions or sandy soils promote faster carbon losses. SOC sometimes decreases when cover crop biomass is low, rapidly decomposes, or has a low C/N ratio. In this case, the carbon added may not be enough to compensate for the stimulation of microbial activity and soil disturbance associated with cover crop termination. High N inputs or wet soil conditions can accelerate decomposition and microbial respiration, sometimes leading to overall SOC losses. Likewise, in coarse-textured soils or warm climates, carbon may turn over too quickly for net gains to accumulate.
| Literature references | Cover crops (all types) |
|---|---|
| Han et al., 2017 | N2O emissions from grain cropping systems: a meta-analysis of the impacts of fertilizer-based and ecologically-based nutrient management strategies |
| Jian et al., 2020 | A calculator to quantify cover crop effects on soil health and productivity |
| Abdalla et al., 2019 | A critical review of the impacts of cover crops on nitrogen leaching, net greenhouse gas balance and crop productivity |
| Li et al., 2023 | The role of conservation agriculture practices in mitigating N2O emissions: A meta-analysis |
| Muhammad et al., 2019 | Regulation of soil CO2 and N2O emissions by cover crops: A meta-analysis |
| Basche et al., 2014 | Do cover crops increase or decrease nitrous oxide emissions? A meta-analysis |
| Jian et al. 2020 | A meta-analysis of global cropland soil carbon changes due to cover cropping |
| Brohoussou et al., 2022 | Management of cover crops in temperate climates influences soil organic carbon stocks: a meta-analysis |
| Shackelford et al., 2019 | Effects of cover crops on multiple ecosystem services: Ten meta-analyses of data from arable farmland in California and the Mediterranean |
| Crystal-Ornelas et al., 2021 | Soil organic carbon is affected by organic amendments, conservation tillage, and cover cropping in organic farming systems: A meta-analysis |
| Bai et al., 2020 | Strategies to mitigate nitrate leaching in vegetable production in China: a meta-analysis |
| Alvarez et al., 2017 | Cover crop effects on soils and subsequent crops in the pampas: A meta-analysis |
| Joshi et al., 2023 | A global meta-analysis of cover crop response on soil carbon storage within a corn production system |
| Blanco-Canqui et al., 2023 | Do cover crops impact labile C more than total C? Data synthesis |
| Hao et al., 2023 | Are there universal soil responses to cover cropping? A systematic review |
| Ceschia et al. 2017 | Potentiel d’atténuation des changements climatiques par les couverts intermédiaires |
| McClelland et al., 2020 | Management of cover crops in temperate climates influences soil organic carbon stocks: a meta-analysis |
| Hu et al. 2023 | Soil organic carbon fractions in response to soil, environmental and agronomic factors under cover cropping systems: A global meta-analysis |
| Villat et al. 2024 | Quantifying soil carbon sequestration from regenerative agricultural practices in crops and vineyards |
| Hu et al. 2023 | Soil organic carbon fractions in response to soil, environmental and agronomic factors under cover cropping systems: A global meta-analysis |
| Poeplau and Don 2015 | Carbon sequestration in agricultural soils via cultivation of cover crops – A meta-analysis |
| Crystal-Ornelas et al. 2021 | Soil organic carbon is affected by organic amendments, conservation tillage, and cover cropping in organic farming systems: A meta-analysis |
| Joshi et al. 2023 | A global meta-analysis of cover crop response on soil carbon storage within a corn production system |