Why it always pays to reseed old pasture

THERE is huge variation in grass production on Irish farms. There are many reasons for this variation such as soil type, rainfall, drainage problems but the most common cause is poor sward quality and lack of perennial ryegrass in grassland.

It’s difficult to get good animal performance from old pasture with some old pasture only producing 50 per cent of the grass dry matter of recent well managed reseeds. Research indicates that successfully reseeding these old pastures will increase production by 3t grass dry matter/ha/year.

Before reseeding any drainage problems should be identified and any drainage required should be addressed if possible. Perennial ryegrass does not survive well in very wet soils. Soil fertility should also be assessed by soil testing and any lime, phosphate and potash applied. This can be done during the reseeding process.

Reseeding can be done from now on until September but spring can give more reliable results and can result in no drop in overall production of grass dry matter for the year. Reseeding can be done with conventional ploughing and harrowing or with a variety of surface cultivation methods. The benefit of surface seeding is that there is minimal burying of surface fertile soil and little or no stones will need to be picked. Surface seeding also can be carried out relatively quickly. A popular system of surface cultivation is one pass of a disc harrow combined with one pass of a power harrow. The top 2 inches is harrowed and this ensures quick germination of grass seeds. The grass seed can be sown in conjunction with the power harrow. It is important to roll the seedbed after sowing. Ploughing also has its place on land that has poor drainage or pan formation in the soil profile.

Some thought should be given to choice of grass varieties to be used. Production and persistency qualities are the two most important traits in grass varieties. Heavy soil mixtures should be made up of predominately late diploids while on better soils some intermediates diploids can be used. Tetraploids should not exceed 30-40% of the grass seed mixture. 3-4 different grass varieties are sufficient in any grass seed mixture. A clover inclusion rate of 0.5 kg should be incorporated in most mixes. Recommended seeding rates are 14 kgs per acre. Consideration should also be given to land use – grazing or silage or both?

Lime at 2-3 tonnes per acre is generally applied at sowing. Bag lime is a worthwhile alternative to ground limestone at reseeding. Standard fertilizer recommendations are 2-3 bags of 18-6-12 or 10-10-20 per acre at sowing but account should be taken of soil tests and nitrates restrictions.

When reseeding always spray with glyphosate a minimum 6-7 days before cultivating. It’s also advised to apply a post-emergent herbicide 30-35 days after sowing to control broad leaved weeds. Grass reseeds can usually be grazed 60-70 days after sowing.

Small cattle or sheep are ideal for the 1st grazing. It’s very important to graze new reseeds at least once before the winter as this encourages tillering and ensures a dense sward the following year. If possible reseeds should not be used for silage on the year of sowing though this is not always practical.