The benefit of white clover in grassland in terms of savings in fertilizer and increased animal performance has previously been shown at a number of experiments undertaken at Teagasc Moorepark and Teagasc Clonakilty.
Currently there is increased interest in white clover as the cost of nitrogen fertiliser continues to increase, and application rates are limited under the Nitrates Directive.
Clover fixes atmospheric nitrogen and makes it available for grass growth.
Previous research has shown that clover can contribute up to 100kg N/ha/yr through nitrogen fixation, resulting in significant savings for farmers.
White clover, however, can also increase both animal and herbage production when compared to grass only swards. Recent research at Teagasc has shown increases in animal performance; milk solids production increased by between 40kg to 65kg milk solids/cow/yr, which can result in additional milk revenue of up to €180/cow/year.
The 15pc increase in animal performance is particularly in the second half of the lactation
when sward clover content is at its greatest.
Clover growth is very seasonal, and therefore its contribution to sward herbage mass varies across the year.
It is lowest in spring, peaking in late summer and declining during autumn.
When included in grass swards it has been shown to increase overall herbage production by between 900kg to 1500kg DM/ha.
overgrown meadow young white clover (Trifolium repens) as a background
As a result of the increase in farm performance there has been an increased interest in incorporating clover into the grazing system.
However, the question arises, how do you get clover into your swards?
Direct reseeding is very successful method; however, this will take a number of years to establish clover over the entire grazing area.
A simple and low cost method of introducing white clover onto your farm is to over-sow the seed into existing grass swards.
Soil Fertility
Clover will establish and persist only on high fertility soils. Rhizobia bacteria that fix nitrogen in association with clover are more productive in soils with a pH of greater than 6.3.
The phosphorus (P) content of the soil is also important when establishing a clover sward.
White clover seeds are very small and clover seedlings tend to be relatively fragile.
Seedling vigour is favoured by having plenty of P in the vicinity of the establishing seedling.
It is usually recommended that clover seed is broadcast with a fertilizer that contains P fertiliser as this will favour establishment; generally 0-7-30 or 0-10-20 is recommended.
Michael Egan works in the Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co Cork.
How to establish white clover
Clover can be established on your farm using two methods: Direct reseeding and Over-sowing.
Direct Reseeding
Key steps involved in a full reseed
Analyse a representative sample of soil for P, K and pH; if ploughing take sample subsequent to doing so;
Spray off the old pasture with a minimum of 5 litres per ha of Glyphosate; allow 7 - 10 days after spraying before cultivating;
Avoid ploughing too deep (15 cm) as it can reduce soil fertility;
Prepare a fine, firm seedbed and apply lime, phosphate and potash as per soil test results;
Avoid sowing clover seed too deep as have poor seed reserved - approx. 10mm;
Ideally cover seeds and roll well to ensure good contact between the seed and the soil.
Over-sowing
Over-sowing is a simple and low-cost method of introducing white clover onto your farm.
Success is very much dependent on weather conditions around sowing; therefore there is a certain amount of risk associated with this approach.
Key steps involved with over-sowing white clover;
When over-sowing, the clover seed can be broadcast onto the sward or stitched in using a suitable machine
Best practice is to over-sow directly after grazing (<4 cm post-grazing sward height) or as after cutting the paddock for surplus bales - it is not recommended to over-sow clover into dedicated silage paddocks;
A slightly higher seeding rate (3.5 to 5kg/ha) is recommended for over-sowing compared to a full reseed, to overcome the issues with slugs and a lower germination rate;
Sow with a fertilizer that contains P fertiliser as this will favour establishment particularly is soil fertility is poor
1 bag of 0-7-30 or 0-10-20/acre
If possible reduce N fertiliser post over-sowing;
Soil contact post sowing is one of the most crucial factors effecting germination
Roll paddocks post sowing to ensure soil contact
Apply watery slurry (if available) - ideally around 2000 gals/acre;
Ideally over-sow on well managed grassland - not suitable on old 'butty' swards with a low content of perennial ryegrass - if this is the case a full reseed is best practice.
Conclusion
White clover can play a significant role in increasing animal performance (+40kg milk solids/cow) and herbage production (+900kg DM/ha) and a potential reduction in chemical N fertiliser.
To avail of this potential benefit white clover can be established by two methods, a full reseed or over-sow.
However, for either method to be successful soil fertility must first be increased to index 3 for P and K and a soil pH of 6.3, if soils are suboptimal.
For full reseeding, white clover sowing rate should be 1 to 2 kg/ha, it is very important that seed is not buried too deep and a good soil seed contact is established.
In an over-sowing scenario the
white clover sowing rate should be 3.5 to 5kg/ha, and again, good soil seed contact is essential.
It is best to carry out over-sowing after a tight grazing or a surplus cut of silage in the months of April to early August to ensure adequate soil temperature for seed germination.
