Benefits of grass/clover swards compared to grass swards
- Can produce similar dry matter yield as a grass sward receiving 200 KG of fertiliser nitrogen per hectare (6 bags of 27 percent nitrogen per acre)
- Maintains high digestibility over longer period leading to improved intakes
- Up to 10 percent higher liveweight gain in cattle, 20 percent more milk from dairy cows and 25 percent higher liveweight gain in sheep
- Enhances lean meat gain and milk protein content
- Contains more minerals, in particular magnesium, thereby reducing the risk of animal health problems associated with mineral deficiency
- Saves on energy usage thereby indirectly reducing environmental pollution
- Evidence of reduced nitrogen loss to the environment
- Greater biodiversity
Clover is the key to organic grassland management
The provision of good levels of herbage production on organic farms depends on achieving high clover contents in swards.
The ability of clover to capture nitrogen from the air is well known but the potential value of clover-based swards is often underestimated.
However, maintaining the high clover contents in swards required to achieve satisfactory levels of production needs careful sward management.
Choice of clover varieties
White clovers are classified according to leaf size:- small, medium, large and very large.
Small leaved varieties survive best under intensive sheep grazing as they have a creeping growth habit. However, they can be expensive, and some varieties can, at times, be in short supply.
Medium leaved varieties are generally tolerant of a wide range of conditions and should always be included in mixtures intended for all grazing uses.
Large leaved varieties are for general purpose use and are best suited to rotational grazing by cattle or sheep or where some silage is taken.
Very large leaved varieties are high yielding but are least persistent under grazing and are best confined to hay or silage swards with only limited grazing use.
The best compromise is to use a mixture of clover varieties, half of which should be medium leaved. The remainder should be either small, medium or large leaved varieties depending on the intended sward use.
Varieties such as Crusader, Chieftain and Barblanca grow earlier in the spring.
The table below shows the most readily available recommended varieties in Northern Ireland.
White clover performance
|Control yield (t DM/ha) 4.3||Relative leaf size percent of Huia||Clover yield potential percent of control||Grazing persistence 0-9|
|Very large leaved|
Note: Varieties in bold type have performed best over many trials
Choice of companion grass for clover
Intermediate heading perennial ryegrasses, particularly some tetraploid varieties, are the best companion grasses for clover. Varieties need to be selected with care.
- Select erect, less aggressive types such as Foxtrot, Spelga and Portstewart. These types develop a sward structure which will help encourage the spread of clover
- Tetraploid varieties such as Dunluce, Aberglyn, Delphin and Dunloy may assist in maintaining an open sward, which should help to promote a higher clover content
- Hybrid ryegrass varieties, which combine the characteristics of perennial and Italian ryegrasses, should encourage clover development due to their more open structure
When reseeding on heavy soils, it may be worth replacing 2-3kg/Ha of perennial ryegrass with Timothy such as Comer, Comtal or Motim
The inclusion of herbs, such as Chicory, Ribgrass (Ribwort plantain) or Bird’s Foot Trefoil, can also be considered on organic farms. Although many herbs will germinate and grow quite readily in reseeds they can be difficult to maintain over time and add to the cost of seed mixtures. They are deep rooting and provide a rich source of minerals and tannins to grazing livestock. Herbs can alternatively be sown in areas of fields where grazing can be controlled.
When the primary use of a sward is silage rather than grazing the use of red clover with Italian and hybrid ryegrasses could be considered.
Establishing clover-rich swards
There are several ways of achieving clover-rich grass swards:
Direct reseeding before the end of August is the most reliable method of establishing grass/clover swards. To ensure a good establishment of clover, be generous with the clover seed and economise on the grass seed.
The best compromise is about 25 KG of perennial ryegrass with 4-5 KG of clover seed, sown at about 30 KG per hectare. The seedbed should be firm and fine and should be rolled prior to sowing the grass/clover mixture.
Undersowing can be useful for spring reseeds, using early maturing spring cereal varieties as the cover crop.
Overseeding methods can be used to place seed into an existing sward, such as direct drilling using the Vertikator, very light cultivation followed by sowing with an air seeder such as the Einbock, Guttler or discing ground and broadcasting the seed.
In all cases it is essential that competition is minimised by grazing the sward tightly (4-5 cm) in late July, or by following in immediately after a silage cut taken mid-July to late August, with soil conditions neither excessively wet nor dry.
Strip or slot seeding can also be used to upgrade existing swards but the technique has given variable results under local conditions.
Minimal cultivation represents an alternative to strip or slot seeding in that the technique does not involve ploughing. If discing, set the disc with minimum cut (coulters running straight) and add weight.
Disc the field in several directions to open up slits in the ground before sowing when soil conditions are dry. Roll after sowing to achieve good seed to soil contact, conserve moisture and ensure rapid germination.
Slurry seeding may be an option in circumstances where the existing sward has become thin and in need of rejuvenation.
Pasture management to encourage clover can have a significant impact provided clover is well distributed throughout the field at the outset.
Key factors in reseeding
All the basic principles for any reseeding operation must be considered as part of an overall sward improvement programme, for example, adequate drainage, pH, fertility, weed and pest control.
Soil analysis to keep a check on soil fertility is worthwhile every three to five years.
Soil samples should be taken from any fields to be reseeded. Aim to maintain a soil pH status of 6.0-6.5, using lime to correct it.
In addition to manure and slurry, some natural sources of phosphate and potash, such as ground rock phosphate and rock potash, can be used to maintain soil fertility. If applying rock phosphate, evidence of need is required under the Phosphate regulations.
For successful clover establishment, by any method, there are some principles that must be adhered to:
- Correct timing - Late summer (August) is best for seed germination and full plant development before winter
- Proper soil fertility - Soil phosphate and potash status should both be at least index 2 and soil pH should be between 6.0 and 6.5
- Good seed/soil contact - Seeds need to be placed into a firm, shallow (1-2 cm) seedbed
- Control grass competition - The existing grass sward cover must be kept low before and after seed sowing, otherwise the young seedlings will not survive
Encouraging clover in existing swards
Provided clover is well distributed throughout the field, even though it may not be contributing much to sward productivity, it may be possible to encourage the development of a productive clover rich sward without the need to reseed.
To determine the suitability of a field for rejuvenation there must be a high proportion of productive grass species present and a clover assessment should be carried out.
As you walk across a field you must see clover within 0.5 m of your foot in 8 out of every 10 inspections, preferably carried out every 20 paces over the entire area of the field.
If there is an even distribution of clover throughout the sward, adopt the management guidelines given below:
- Graze hard (3-5 cm) with sheep or light cattle during November/December
- Avoid under-grazing during spring/early summer
- Rest for three to four weeks during July or closing off for silage
- Avoid poaching
- Avoid smothering with slurry
- Avoid spreading silage effluent
- Control broad leaved weeds
In direct sown swards, or swards undersown in an arable silage crop, topping or forage harvesting can control many weeds.
Grazing with sheep whenever the grass is 10 cm tall can provide a useful degree of control of annual weeds like chickweed, hempnettle and redshank. This can also help control ragwort in established swards.
However, care must be taken to avoid overgrazing and poaching, especially when soil conditions are wet. Periods of frost can provide an opportunity to graze with minimal damage.
Thistles do not survive long if repeatedly topped before flowering. Docks are the most difficult weed to control in an organic system and regular topping to prevent flowering is recommended.
Pest and disease control
Clover is even more susceptible to leatherjackets than grasses, although clover will eventually recover after most attacks.
Although a number of diseases can affect both white and red clover there are no routine recommendations for their control.
Bloat can occur in both beef and dairy cattle grazed on lush, clover-rich swards. However, the condition can also occur on all-grass swards.
As part of normal rumen function the large volumes of gas normally produced are belched and the animals suffer no discomfort.
However, when bloat occurs a stable froth is produced which inhibits both normal belching of the gas and rumen contractions.
Sub-clinical and clinical bloat can affect productivity, while in severe cases death can result from heart failure and from asphyxia.
- Feed roughage, such as straw or hay, before turning out and, if necessary, during grazing
- Sheep selectively graze clover and are not prone to bloat. Grazing sheep ahead of cattle reduces the risk
- Never allow hungry cattle to gorge themselves on clover-rich pasture
- Cattle moved onto dry rather than wet pasture are at less risk
- Affected animals may be treated with antifoaming agents
- In severe cases remove animals from clover swards and seek veterinary advice
Fluctuations in production
The productivity of grass/clover swards can be more variable, both within and between seasons, when compared to grass swards dependent on artificial nitrogen fertiliser.
Clover-based swards are slow to start growing in the spring. Early growth can be encouraged through strategic use of slurry and farmyard manure. It is important that the resultant flush of grass is grazed down efficiently to allow subsequent growth and development of clover within the sward.
Target clover content
In most situations the clover content of swards is at its peak from late July to mid-August. The spring target should be 30 percent ground cover, indicating that adequate clover has survived the winter and that it will be able to compete with grasses that grow more quickly than clover in spring. Ground cover is the proportion of the ground covered with clover leaves.
By mid-June, clover ground cover should be increasing to about 40 percent. A peak of 50-60 percent clover ground cover is required by early August. This results in the best compromise between the quantity of herbage produced per hectare and the nutritional value of the herbage.
If the clover content is very high, overall yield decreases, since there is not enough grass to utilise the nitrogen fixed by clover. While the nutritional value of the available herbage rises, the risk of bloat in cattle is also increased. However, too little clover will eventually result in poor production.
The proportion of clover required to improve individual animal performance depends on the type of stock and the grazing system adopted.
For example, sheep in rotationally grazed swards can show enhanced performance with an average clover cover of 20-30 percent over the season. This is due to their ability to selectively graze clover.
In set-stocked systems sheep performance has benefited from the presence of a lower content of clover (less than 20 percent cover) over the season.
In cattle systems, swards need to contain 4055 percent average cover in order to enhance individual animal performance.
All seed sown on organic farms should be certified as organic. Organically produced seed can be in short supply, so if sufficient suitable organic seed cannot be sourced producers must request a derogation from their sector body to use untreated non-organic seed.
However, the proportion of non-organic seed allowed is reducing year by year.
Further Reading (DARD booklets)
'Grass and Clover–Recommended Varieties for Northern Ireland'
‘Clover – good for …’
© CAFRE - October 2010