Dairy notes August 2008

Grazing Management

With excellent growing conditions and after-grass coming into the grazing system, grass supplies will have to be carefully monitored to ensure they don’t become too strong for grazing. Good quality August/September grazing is capable of producing 15-17 litres of milk. Swards should be grazed with a cover of 3300-3500 KG DM/ha (16-18 cm. high).

To ensure good quality regrowth throughout the rest of the season, swards need to be well grazed out, down to a residual cover of 1600-1800 KG DM/ha.

If necessary use a group of dry cows or young-stock as followers to the milking cows to ensure swards are well grazed without penalising yield. On heavily dung-patted areas use the grass topper.

Sward Improvement

With straight nitrogen prices predicted to be over £400 /tonne next spring some thought should be given to the value of establishing and managing clover in at least some of your grass swards. White clover based swards are capable of producing the same amount of forage as a sward receiving up to 200 KGs of nitrogen / ha (14 bags of 27.5 percent N/ha). Are the fields grazed by heifers receiving as much fertiliser as this? By establishing white clover swards, you should be able to cut out mid and late season fertiliser applications. On farms with an arable rotation the use of red clover in silage swards could also be considered.

With a total seeding rate of 30KGs seed/ ha grazing mixtures should include 4-5 KGs of white clover seed. For cattle grazing a mixture of medium (Aberdai, Crusader, Chieftain) and large leafed (Alice, Barblanca) clover varieties should be used. Intermediate and late heading perennial ryegrasses are the best companion grasses for the clover. Use more erect growing less aggressive diploid varieties such as Aberavon, Aberstar, Foxtrot and Pastour along with some of the less dense tetraploid varieties such as Greengold, Garibaldi, Delphin and Navan to establish a sward structure which will encourage the clover to spread.

Soil fertility is crucial in establishing and maintaining clover in swards – soil pH should be 6.0 - 6.5 and phosphate and potash levels index 2. Carry out soil analysis to identify what lime and fertiliser treatments are required.

Clover swards should be sown by mid-August. Poorly established clover seedlings in late sowings are at greater risk of winter kill than grass plants. There are several methods of establishing clover rich swards :

Direct Reseeding

The most reliable method of sward establishment but the highest cost option.
Where docks and bents are a particular problem, the old sward needs to be burnt off use a glyphosate spray 10 – 14 days before ploughing.
Use two runs with a power harrow to prepare the seed bed, roll, sow and then roll again. Rolling before sowing ensures the tiny clover seed is not buried too deep.

Minimal cultivation

Can be used on shallow soils or stony ground where ploughing is not an option.
Burn off the old sward with glyphosate. After seven days prepare the seed bed with two runs of the power harrow. The bed can also be prepared using a disc harrow with the discs set with minimum cut (coulters running straight) and weight added.
Roll after sowing to ensure good soil to seed contact.

Overseeding

Can be used to establish clover in an existing good quality perennial ryegrass based sward.
A number of techniques can be used – light cultivation followed by sowing with an air seeder such as the Einbock; direct drilling using a Vertikator; discing and broadcasting the seed; slurry seeding thin swards.
With all methods it is essential that competition from established grasses is minimised by either grazing the sward tightly (4-5cm) before treatment or following immediately after a silage cut.