23 August 2002

PUT SOME ZIP IN YOUR GRASS

Productive pastures form the bedrock of most successful

sheep enterprises. Marianne Curtis seeks a few tips

on how to put the spice back into tired pastures

IN TIGHT times, the prospect of parting with £250/ha (£100/acre) to reseed paddocks may seem daunting and many are considering pasture renovation as an alternative this year.

But simply overseeding existing pasture and hoping grass will establish is likely to bring disappointment.

Successful pasture renovation requires careful planning, says Francis Dunne of Oliver Seeds. "Renovation using overseeding techniques often lacks reliability. When seed fails to establish, producers often ring seed merchants complaining the seed is poor. But frequently soil structure or nutrition are to blame.

"Unless these issues are addressed, buying more seed will be a waste of money. Correcting soil structure and nutrition may even make overseeding unnecessary."

The first step in pasture renovation is to analyse the soil, says Mr Dunne. "As well as NPK and pH analysis, consider a more detailed Albrecht type analysis. This measures levels of a range of trace elements and includes information on nutrient availability, relating ideal nutrient levels to soil type."

Once soil nutrient problems have been corrected, soil structure should be checked, he says. "More yield potential is probably locked up by poor soil structure than by any other issue. The roots of a plant can be compared with an animals mouth. Compacted soil is the equivalent to having your jaw wired."

Using a compaction tester or digging a hole can pinpoint compaction problems. A compaction tester comprises levels of oil in a steel tube and contains a pressure gauge, says Mr Dunne. "When pushed into the ground, it indicates tough layers of soil. When using a spade, the levels which are most difficult to dig through will be compacted.

"Compacted layers also appear as horizontal fracturing in a dry profile. Healthy soil structure is well fissured both vertically and horizontally. Looking at root depth is also an indicator of problems; shallow roots show soil penetration is poor."

Ways of improving soil structure vary depending on the depth of compacted layers (table 1).

Once soil structure has been dealt with, the next stage is to check sward composition, says Mr Dunne. "For pastures reseeded 3-4 years ago which are open, but predominantly perennial or hybrid ryegrass, overseeding is appropriate.

"However, for thick permanent pasture, it is best to take a cut of silage before seeding. This opens the sward, creating better conditions for establishment. But using a weed rake to sow seed in this situation can be problematic, as grass left from silaging becomes tangled in tines."

With swards dominated by creeping grasses, such as couch and bents, there is no point in reseeding until these are killed, says Mr Dunne. "The best approach is to cut silage, which opens pasture, then spray with glyphosate. Spray in September, while grass growth is good, so the chemical is effective. By spring a frost tilth will have developed ready for reseeding without ploughing.

"Spring reseeding will allow grass to become well established by the following winter and able to withstand any flooding which may occur in areas such as river meadows."

Seeding methods include slot seeders, direct drills or harrow combs. All work well, but certain machines are best suited to particular circumstances, he says. "Slot seeding is most appropriate for permanent pasture, as it cuts a wide slit, creating a tilth away from the sward surface.

"But this method is unsuitable for uneven surfaces, such as ridge and furrow land. Harrow combs cope better with uneven land. Contractors with experience in reseeding, should be able to advise on the most suitable machine."

Pest control is also an important aspect of any pasture renovation programme, says Mr Dunne. "Sowing grass and clover as part of a pasture renovation programme is risky. You are establishing seedlings in an environment already populated by species most likely to attack them."

There are two ways of minimising pest damage. The first, particularly important for organic producers, is to avoid sowing at times of year when pests are most likely to be a problem (table 2). "Pest populations are lowest in spring and early summer," says Mr Dunne.

When sowing at other times of year, conventional producers should consider chemical pest control, he advises. "Frit fly and sitona weevils can be a problem in the August-October period. In damp conditions, slug control is also a key issue, particularly when using slot seeders and direct drills."

Livestock can also hinder establishment. Although it is safe for them to graze pastures in the first 7-10 days after seeding, they should be removed after this period, he advises.

"This is particularly important with sheep, which will pull up what you have just planted. Ideally, shut reseeded ground up for silage at this point, returning livestock to it about three weeks after cutting." &#42

Correcting any problems in the field is vital to get a good crop when renovating pastures, says Francis Dunne.

&#8226 Check soil nutrients.

&#8226 Improve soil structure.

&#8226 Deal with pests.


Depth of problem Symptoms Action When

Surface 0-2cm Hard surface, Harrow comb Any time

sod pulling

Shallow 0-10cm Hard surface, Spike aerator Autumn/spring

poaching,

sod pulling

Medium 0-25cm Poaching/shallow Tined aerator Summer/autumn

plough pan

Deep 20-40cm Plough pan Subsoiler/flat lift Summer/autumn


Pest Main problem period Species affected

Slugs Cool, wet conditions, Clovers and grasses

particularly autumn/winter

Frit fly July-October Italian and perennial ryegrass

Sitona weevils July-October Clovers

Leatherjackets March-May Clovers and grasses