White Clover and reducing chemical fertiliser usage

Researcher Michael Egan tells us why clover has an important role to play in reducing chemical fertiliser usage on grassland farms in Ireland. There is also advice on establishing a white clover sward.

Recent research in Teagasc Moorepark has shown:

• increases in milk of +30 kg milk solids/cow/year
• increase in herbage production of +1100 kg DM/ha/year
• reductions in N fertiliser by up to 100 kg N/ha from incorporating white clover into grass-swards in high stocking rate systems.

To date the uptake of meaningful inclusion of white clover in swards on commercial farms has been low. There has been an increase in white cover use on farm this current year with increasing fertiliser prices and environmental concerns. Reseeding an entire farm to introduce white clover into pastures is impractical and costly and as such there must be a two pronged approach;

1. reseeding
2. over-sowing

to introducing white clover onto grassland farms.

Establishing a white clover sward on your farm

Incorporating white clover in a full reseed is the most reliable method of establishing white clover and provides the best opportunity for weed control. Over-sowing is a simple and low cost method of introducing white clover into swards and can yield successful clover establishment; however, success is very much dependent on;

• soil fertility
• soil moisture
• post-sowing grazing management
• competition from the existing sward.

Suitable paddocks for over-sowing are those with good soil fertility, index 3 or 4 for P & K, and a soil pH of >6.5, high perennial ryegrass content and low weed content.

When selecting clover cultivars to sow, use the department recommended list. Small and medium leaved cultivars are best suited to intensive grazing systems.  Large leaf white clover and red clover are more suited to silage-based systems. White clover should be sown when soils are warm and moist – ideally in April/May. Sowing in the autumn can reduce chances of a successful establishment as soil temperatures are on the decline so it is more difficult for clover to compete with the grass. If Irish farms are to successfully establish clover as part of their grazing system, it will need to be undertaken over a period of time, 3 to 4 years and use a combination of methods.

White Clover Establishment Blueprint

A targeted multiyear approach should be used in establishing a white clover system- combination of reseeding and over-sowing

• Reseed approx. 10% per year
• Over sow approx. 20 % per year
• Yr 1- reseed 10% & over sow 20% = 30%
• Yr 2- reseed 10% & over sow 20% = 30% (60%)
• Yr 3 – reseed 10% & over sow 20% = 30% (90%)
• Yr 4 - remaining 10% + any ground that clover didn’t establish on (100%)

Paddocks for a full reseed should be identified as early as possible in the process to avoid over-sowing clover on these.

Direct Reseeding - Key steps involved in a full reseed

• Take a representative soil sample for analysis of P, K and pH; if ploughing take sample after ploughing
• Spray off the old pasture with glyphosate as per label recommendations; allow a minimum of 7 to 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, P and K as per soil test results
• Sow grass at 34 kg/ha and white clover at 2.5 to 3.5 kg/ha seed mix
• Avoid sowing white clover seed too deep; sowing depth – approx. 10 mm
• Ideally cover seeds and roll well to ensure good contact between the seed and the soil               

Over-sowing - Key steps involved with over-sowing white clover

• When over-sowing, the white 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 after cutting the paddock for surplus bales – ideally only over-sow 3 to 4 paddocks at a time
• Control weeds before you consider over-sowing clover - some herbicides have a residue of up to 4 months – always check the residual time on the label of the product or seek advice on a suitable weed control product
• A slightly higher seeding rate (5 - 6 kg/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 fertiliser that contains P as this will favour establishment particularly if 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 over-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 gallons/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
• If broadcasting with a fertiliser spreader - mix clover seed with 0:7:30 fertiliser and only add clover to the spreader when you are in the field, to avoid clover settling at the base of the spreader