Incorporate legumes in grassland
System: Dairy cattle
Mainly applicable for: Grass-based systems
Not applicable or effective for: No grassland
Description
Incorporating and maintaining clover into grassland, by either reseeding or over-sowing clover into existing grassland. Clover can fix between 60-150 kg N/ha per year (dependent on sward clover content), which reduces the need for synthetic nitrogen fertilizers to maintain herbage production. Over-fertilization with nitrogen can reduce clover content as clover does not thrive with high nitrogen fertiliser application rates. In most cases manure application in spring is beneficial because temperatures are often too low for effective N fixation by clover, and the nitrogen supplied by manure can enhance yield in the first cut. White clover is generally appropriate for grazing, while red clover is often used for mowing fields (silage and hay).
In this factsheet we assumed synthetic nitrogen fertilizer is reduced or eliminated with the introduction of grass-clover swards.
Mechanism of effect
Incorporating clover into swards enables biological nitrogen fixation, which reduces the need for synthetic nitrogen fertilizer as clover can fix atmoshperic nitrogen into plant available forms of nitrogen. This reduces the nitrous oxide and carbon dioxide emissions associated with the production and transport of nitrogen fertilizers. Depending on the situation, clover may enhance herbage yields and increase milk yield and solids production, and thereby, reduce emission per unit of milk produced. Also, depending on the situation, incorporating clove may increase the sward crude protein content and reduce the need for protein-rich concentrates and associated CO2 emissions and land use change (LUC). Greater plant species richness can also have benefical effects on soil organic carbon (SOC) content and soil fertility. However, maintaining certain species in pasture (“persistence”) can be a challenge and might require more often renovation, which will reduce SOC benefits.
Reference situation
Grass-only sward (N-fertilized)
Legend
| ● – Small effect (<5%) | o – No effect | o – no effect |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | ? – unknown effect |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) |
Effect on total greenhouse gas (GHG) emissions
| Mean effect and range in kg CO2-equivalents: | per kg product | per farm | Level of evidence | ||
| Mean | (min-max) | Mean | (min-max) | ||
| Grass-clover compared to grass only | ●● | ●–●● | ● | ●–●● | Medium |
Effect per emission source
| Source | Manure storage | Animals | Feed and forage production | Barn | ||||
| Gas | CH4 | N2O | CH4 | CO2 | N2O | LUC | CO2 | |
| Grass-clover compared to grass only | ●● | ● | ● | ● | ||||
*risk of an adverse effect (see ’cause of variable or unfavourable effect’)
Effect on soil organic carbon (SOC) stocks
| Relative change (%) in SOC%: | ||||
| Mean | (min-max) | Level of evidence | ||
| Increase plant species richness | ● ● | ● – ●● | ||
| ● – 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) |
Cause of variable or unfavourable effect
Grass-clover compared to grass only
Effects depend on the initial situation regarding soil N balance and nutritional value of the feed. Nitrous oxide emissions from soils can increase if synthetic N fertilizer is not sufficiently reduced in the grass-clover swards. High nitrous oxide emissions can be expected if high N surpluses coincide with high soil carbon stocks, which is more likely in older grassland swards (Reinsch et al., 2020). Also, grass-clover mixtures produce higher quality forage compared to grass-only swards, which can increase milk production and improve the feed efficiency of dairy cows, but increase absolute methane emission due to a higher dry matter intake (Van Gastelen et al., 2018). Also, the higher crude protein in swards can increase nitrous oxide emissions from manure if there is excess nitrogen in the diet.
Increase plant species richness
The effect on SOC depends on plant species composition (species with higher rooting intensity will increase SOC) and species density; share of legumes in the composition (legumes have lower C:N ratio which might enhance decomposition); climate (smaller SOC increase in warm and dry conditions) and soil texture (higher SOC increase in fine-textured soils). Maintaining certain species in pasture (“persistence”) can be a challenge and might require more often renovation, which will reduce SOC.
| Literature references | Grass-clover compared to grass only |
|---|---|
| Herron et al., 2021 | The simulated environmental impact of incorporating white clover into pasture-based dairy production systems |
| O’Brien et al., 2024 | Environmental impact of grass-based cattle farms: A life cycle assessment of nature-based diversification scenarios |
| De Souza Congio et al., 2021 | Enteric methane mitigation strategies for ruminant livestock systems in the Latin America and Caribbean region: A meta-analysis |
| Reinsch et al., 2020 | Nitrous oxide emissions from grass–clover swards asinfluenced by sward age and biological nitrogen fixation |
| Enriquez-Hidalgo et al., 2014 | Milk production and enteric methane emissions by dairy cows grazing fertilized perennial ryegrass pasture with or without inclusion of white clover |
| Yan et al., 2013 | The carbon footprint of pasture-based milk production: Can white clover make a difference? |
| Eugene et al., 2021 | Methane mitigating options with forages fed to ruminants |
| Tamburini et al., 2020 | Agricultural diversification promotes multiple ecosystem services without compromising yield |
| Lee et al., 2004 | Methane emissions by dairy cows fed increasing proportions of white clover (Trifolium repens) in pasture |
| Dwan et al., 2025 | Evaluating the effect of white clover inclusion and dairy cow genetic merit on enteric methane emissions within rotational grazing systems |
| Literature references | Increase plant species richness |
|---|---|
| Wang et al., 2020 | Negative impacts of plant diversity loss on carbon sequestration exacerbate over time in grasslands |
| Shan et al., 2020 | Species richness promotes ecosystem carbon storage: evidence from biodiversity-ecosystem functioning experiments |
| Cong et al., 2014 | Plant species richness promotes soil carbon and nitrogen stocks in grasslands without legumes |
| Chen et al., 2019 | Effects of plant diversity on soil carbon in diverse ecosystems: a global meta-analysis |