White Clover

White clover is the most commonly sown legume species in temperate grassland. White clover grows well in association with grass. It is tolerant of grazing and can grow over a fairly wide range of climatic conditions.

White clover can increase the tonnes dry matter grown, increase animal performance as it is a higher quality feed, and it can reduce the need for chemical nitrogen 

Recognition of the high forage quality and the nitrogen (N) fixation benefits of grass-white clover pastures has led to a resurgence of interest in its use as a means of reducing the economic and environmental costs in livestock agriculture. 

Research is being undertaken at Teagasc Moorepark, Curtins, Clonakilty and Athenry research farms on the role of white clover in our production systems. The research program to date has delivered very promising results including:

• high N use efficiency (NUE) of close to 60%
• lower N surplus
• higher animal performance.

There is, however, a clear challenge to ensure that grass-white clover swards are established and persist on commercial grassland farms.

Benefits of white clover

The benefits of white clover tend to occur from May onwards as sward white clover content increases. The main benefits of white clover inclusion in grass swards are:

• Increased herbage quality compared to grass-only swards in the summer months.
• Increased dry matter (DM) intake in summer and autumn.
• Higher milk production and liveweight gain.
• Nitrogen fixation – white clover fixes N from the atmosphere making it available for plant growth.
• Lower requirement for N fertiliser application in summer.

Nitrogen fixation

Nitrogen fixation is the process whereby white clover can fix N from the atmosphere and make it available for plant growth through a process called biological N fixation (BNF). This N is then available for uptake by white clover and other plants, mainly perennial ryegrass, in the sward. The quantity of N fixed by a grass white-clover sward depends on a number of factors including:

• Sward white clover content – N fixation increases as clover content increases.
• N fertiliser application rate – N fixation declines with increasing N application.
• Soil temperature - N fixation increases as soil temperature increases.
• Solar radiation (sun light) – more sunlight, more fixation.

Typically as N fertiliser application rate increases, N fixation decreases, as there is adequate N available for grass and white clover growth. 

Quantity of N fixed at different N application rates

How does white clover grow

There are three stages of white clover growth from germination to full establishment. These are:

1. Rosette Phase
2. Expansion Phase
3. Clonal Phase

During the rosette and expansion phases white clover relies heavily on a central taproot for growth and development. In the clonal phase the plant is fully reliant on the stolons for growth and persistence.

Rosette Phase

• Reliant on central taproot
• Few branches
• Small spread
• Rosette plant form » Small vertical primary stem surrounded by ring of short secondary branches
• Plant size – 10-20 cm
• Phase lasts approx. three months
• Clover does not fix N in this phase
• Important to graze during this phase to promote growth - without damaging plant

Expansion Phase

• Reliant on central taproot
• Rapid expansion – up to 15 branches, 25-30 cm in size
• Initially rooting is poor on the stolons and careful grazing is required to avoid damage
• Six months post-sowing roots strengthen but plant still reliant on central taproot for nutrient uptake
• 12 months post-sowing taproot begins to die – can take up to 2.5 years for all taproots in the sward to die
• 12-18 months post-sowing N fixation begins
• Good grazing management is crucial for stolon development

Clonal Phase

• No taproot - Reliant on adventitious roots which form at the nodes of the stolons
• Normal status of clover in established swards
• Clover actively fixing N
• Stolons last for 12-18 months. New stolons produced at the terminal bud
• New stolons become independent plants and this cycle continues each year
• Good grazing management helps maintain stolon production and white clover persistence in grazing swards

White clover plant in the clonal phase