Reseeding - sward heath check

Published 24 August 12

Reseeding

Are your swards performing as you would like them to? Do you know which are you best performing swards and which are your worst?  These are the starting points for deciding whether a reseed is the right option to take, according to DairyCo extension officer Chris Coxon.

But, he adds, before considering a full reseed or any improvement strategy for the pasture, it is essential to cost the process carefully in relation to the likely benefits and to run a sward health check.

Sward Health Check

  • The first consideration for the production of quality grass is ryegrass content. Does the sward contain less than the target minimum 50% ryegrass? The aim for is for 70% ryegrass, so clearly levels below 50% need serious attention. 
  • Next sample the soil to check the pH is at 6-6.5 or below and P and K indices are at 2. If they are not plan to remedy this with a suitable lime based product.
  • Check the soil profile for evidence of compaction, soil pans and heavy poaching. Sub-soil any suspect areas.
  • Inspect the drains to ensure they are working properly, particularly in any damp areas.


Following the assessment and correction of these points there are two main choices when looking at full reseeds, either conventional drilling or direct drilling.

Conventional Drilling

For the greatest conventional drilling value spray with glyphosate to kill perennial weeds and inferior weed grasses in particular. Allow 5-7 days, or get agronomic advice, before cultivating for a complete kill.  Then plough-under any previous grass swards or arable residues, and follow this with any required lime and fertiliser. 

Prepare a fine, firm 5-8 cm deep seedbed immediately prior to sowing and sow when soil conditions are neither too wet nor too dry, taking particular care with the timing of clover sowings.

Ensure that you calibrate the drill to the seed mixture used, as this will vary from batch to batch and year to year. Cross-drilling at half the seed
rate in each direction provides better cover, and a similar technique can be used to improve calibration if broadcasting the seed. 

The optimum drill depth for grass seed is 1.5 cm while clover mixtures are best sown with the coulters raised to just scratch the surface.  Consolidate the seedbed after sowing without compacting it, using a combination of flat and Cambridge rolls.

Direct-drilling

The aim of direct-drilling is to minimise the surface trash to give new seedlings the best chance to establish and remove the opportunity of other species to take up valuable water and nutrients from the surrounding soil environment. 

To reduce grass cover, mow the field immediately prior to drilling or graze very close to ground. Spraying with glyphosate, as with the conventional drilling technique, will lengthen the window available to new seedlings to establish. 

Apply lime after spraying, if required, and remove any compaction layers by sub-soiling to a relevant depth just below the target layer. Any deeper is adding unnecessary cost to the operation for no long term benefit.

Drill when the soil is dry and will not smear and use an appropriate drill - either a slot seeder like the Hunter Rotary Strip Seeder or Aitchison Seedmatic , or for very well-grazed swards, open and worn-out ryegrass stubbles, a direct drill such as the Moore Unidrill or Bettison 3D. Again, cross-drilling at half seed rate in each direction will maximise evenness.  Rolling at a slight angle to the slots immediately after drilling also ensures good soil contact. 

This method of establishment warrants a serious consideration of pest control, particularly slug pellets during moist conditions and sprays to kill leatherjackets and frit fly.  Agronomic advice here is valuable as a background level of pests in a compacted highly tillered grass sward will rarely show damage but the same field with young shoots and open soils will mean the odds are stacked against success.

Early Care

Whichever method of establishment is used attending to early management of new leys is important to monitor firstly how well is the crop emerging and also what is its competition. 

  • Weed seedlings should be checked within a month of emergence.  Control at this stage will be much more effective than later on, given the greater susceptibility of weed seedlings to herbicides. 
  • Herbicides should always be selected and applied to tackle specific weed problems, with clover-safe sprays chosen for mixed swards. 
  • New leys generally compete well with pests except when weather conditions limit their vigour, in which case control measures may be needed.