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The best way to reseed grassland

Avoid reseeding problems and get more from grass.

Introduction

Well managed grassland containing modern ryegrass varieties can produce over 14 t DM/ha.

The Benefits of Reseeding

  • Increased total DM production
  • Improved spring and autumn grass supply
  • Produce better quality feed and digestibility meaning increased animal performance
  • Better response to fertiliser, increasing efficiency
  • Increased farm productivity and profitability
  • Access to new breeding genetics
  • Grassland can control blackgrass in arable rotations.

Successful reseeding depends on several factors;

  • field characteristics
  • cultivation techniques
  • soil fertility
  • timing of seeding
  • mixture or seed selection
  • stocking rate
  • grazing and cutting management.

If all of these factors are considered and managed, then your pasture forage can provide the majority of your animal feed requirements.

A healthy pasture will produce a greater quantity of high quality grass meaning better animal performance and reduced feed costs.

Guide

1. Identify fields to be reseeded and plan in advance

How to choose

You need to consider reseeding if you answer yes to some of these questions:–

  • Is the DM yield dropping?
  • Are there fewer grazings taken or less silage from the fields?
  • Are the fields badly poached?
  • Are weeds and weed grass percentages increasing in the fields?

Selecting swards: Aim to reseed 10%–15% of the farm per year.

When to reseed

Spring / Early Summer

Spring or early summer reseeding is preferable in northern and colder areas due to improving soil and air temperatures and ground conditions compared to the autumn.

Improving temperatures in spring along with longer days will help achieve good germination and establishment of the new seed.

Improving ground conditions will enable frequent grazing of the new reseed which is critical to the tillering process, while also allowing more time for use of post–emergence spray, compared to an autumn reseed.

Autumn

Autumn reseeding suits from a feed budget perspective and in arable rotations. The ideal time is during August. Leys with clover should be sown before mid–August. Delaying reseeding into September means possible lower temperatures which can reduce seed germination. Also, more rainfall can result in poor ground conditions, making it difficult to graze which is crucial for tillering of the new sward and reduces the opportunity to use a post–emergence spray.

2. Soil test

Why test?

  • Small cost
  • Valid for 3– 5 years
  • Helps you to save money when you apply correct fertiliser for growing crops
  • Greatly increases your chance of success

What a standard soil test will tell you:–

  • Soil pH –
  • Lime requirement
  • Soil phosphorous (P)Soil potassium (K)
  • It will also provide individual advice on lime, P and K requirements

A more detailed soil analysis can be requested which will provide information on the micro nutrients in the soil.

How to take a soil sample

Divide farm into 2–4 ha areas that can be managed individually for a specific fertiliser application program.

Take samples from different areas based on:

  • soil type
  • cropping history
  • slope
  • drainage
  • persistent poor yields

TIP – avoid odd spots like old fences, water troughs, ditches or dung patches.

Do not sample a field for P and K until 3 – 6 months after last application of fertiliser P and K (late autumn is a good time to sample).

Where lime has been applied allow a time lag of 2 years before sampling for lime requirements.

  • Follow a ‘W’ soil sampling pattern to ensure that the sample is representative of the entire field.
  • Take approximately 20 cores. Ensure that all soil cores are taken to the full 100mm depth.
  • Place the 20 cores in the soil box to make up the soil sample.
  • Write the field number and sample number on the soil box.

3. Spray off old sward with glyphosate

Before reseeding it is necessary to kill off the old sward. Always follow product guidelines for spray and water rates.

Ensure old sward is growing actively and perennial weeds such as docks are growing well but not too strongly.

After spraying–

Approximately 7–10 days after spraying you should graze / cut as tightly as possible. This is important to ensure a relatively clean seed bed at sowing.

Allow a minimum of 10 days before ploughing, or 16 days for minimum cultivation to allow spray to work properly.

4. Choose the right method of seeding

Each method will differ in cost and also their suitability to different situations and conditions.

Adding Lime–

Apply lime to rectify deficiencies to ground regardless of method of reseeding. The recommendation for reseeding is 5 t lime/ha (2 t lime / acre).
If ploughing apply lime after ploughing and levelling to avoid burying the lime.

Regardless of which method you use – you must prepare a fine, firm seedbed before sowing. The reasons for this are:

  • Ensures good seed to soil contact for germination
  • Firmness is important to avoid seed getting buried too deep
  • With a fine, firm seed bed moisture will be better retained within the soil which is critical for the new plant
  • A level even seedbed helps the sward establish.

Ploughing

Ploughing is widely considered the most consistent and reliable method of establishing a new sward.

Ploughing has the advantage of minimising competition from the existing sward while also burying the weed seeds and removing debris from the surface.

Avoid deep ploughing, as the more fertile top layer of soil will be buried too deep. Ploughing will bring stones to the surface, larger ones will have to be removed before sowing.

Minimal Cultivation

Widely used where ploughing is unsuitable or undesirable, this method involves the cultivation of a shallow seedbed, with a power harrow, rotavator or similar machine. For successful results, ensure the old sward and weeds have been fully destroyed. Minimise the surface thrash by grazing or cutting the dead sward prior to cultivation, apply 5 t lime/ ha (2 t/acre) and ensure adequate rolling to consolidate the seed bed.

Disc and one pass

Aim for 2 to 3 passes of the disc harrow. The second run should be at an angle different to the first run to ensure break of the sod and sufficient soil is turned up. Avoid excessive forward speeds as this can result in uneven seedbeds.

Direct drilling

Specialised drilling machines are used which have a disc or tine to cut a slot in the soil into which the seed is dropped.

Spray off the old sward well in advance of direct drilling and apply lime to counteract acidity as the old sward decays. Rolling afterwards will help maintain moisture in the soil. 
Results can be very variable with this method. The weather following sowing is important – a dry spell can result in failure with this method of reseed.

Slugs are also a major risk with this method of sowing as the slot provides a channel for slugs to move along and feed on the new seedling.

Overseeding

Used to rejuvenate an old sward where full reseeding is not deemed necessary. Results can be variable and are dependent on numerous factors. Good seed–soil contact is essential, therefore this will not work if there is a thatch of grass in the existing sward.

Slot seeding with an appropriate direct drill e.g., Atchinson or Moore UniDrill is the most common method used.

Graze the old sward hard or ideally use this method after taking a heavy cut of silage.
Use a seed rate of 20–25 kg/ha (8 – 10 kg/acre) and graze the sward frequently at light covers to avoid the existing sward shading out the new seeds.

5. Prepare a fine firm seed bed

6. Sow grass seed

Sow at 35–40 kg/ha (14kg–16 kg/acre).

Use the National Recommended List of Grass Varieties to identify varieties with high seasonal and total DM yield, and high quality (DMD or D–value).

Grasses with higher quality have been shown to significantly improve animal performance.

For grazing use diploid and tetraploid perennial ryegrass with high quality and high sugar content. For specialist short term cutting 1–3 years use Italian or Hybrid Ryegrass.

Consider white clover in grazing and dual purpose leys and red clover in cutting leys.

7. Apply fertiliser

It is important to apply Nitrogen (N), Phosphorous (P) and Potassium (K) at sowing.

N is important to provide the seedling with energy for growth.

P and K are important to help the plant with root and tiller development. Both P and K should be applied based on requirements from your soil test results. An additional 15 kg P/ha is permitted in addition to normal allowances for reseeded grassland on index 1, 2 and 3 soils.

The table below shows the permitted P and K rates for pasture establishment

 Soil Index P application rate (kg/ha) K application rate (kg/ha)
 1 60 110
 2 40 75
 3 30 50
 4 0 30 

Before choosing your fertiliser products (especially N and P) please consult your local advisor to ensure that you do not exceed the limits for your farm as determined by the Nitrates Directive.

A further 40 kg N/ha should be applied 3 to 4 weeks after sowing to give the plant adequate energy to keep growing.

8. Roll adequately

WHY?

Rolling helps consolidate the soil to give better germination.

Inadequate rolling may result in poor / patchy establishment of the new grass.

Often it is noticed that the grass grows quickest on the headlands where the machine was turning or along the tram lines in the field, this indicates that the field has been inadequately rolled. Do not roll once plants start to emerge as you will damage the seedling. Adequate rolling should take place at sowing to ensure good soil/seed contact.

9. Check for pests

Always monitor a new reseed for signs of pest attack.

Slugs, leatherjackets, frit–fly and rabbits are the most common problems.

There are now limited options for control of frit–fly or leatherjackets. If you suspect a problem seek further advice from your agronomist.

Direct drilling in the autumn presents the greatest risk, but attacks can happen anytime.

10. Kill weeds with post emergence spray 6 weeks after sowing

Common grassland weeds

Docks and chickweed are the most common problems in new reseeds.

Other weeds e.g. fat hen, charlock, and redshank are unlikely to cause a problem unless present in high numbers.

Weed control in new leys

Post emergence spray is generally applied about 6 weeks after sowing depending on the stage of growth of the grass, clover (if present) and weeds. Seek advice on the most appropriate spray to use from your advisor. If you have clover sown, ensure clover is at trifoliate stage before spraying and use a clover safe spray.

11. Take the first grazing once plants stand the “pull test”

The first grazing should occur at a low herbage mass.

Grazing is critical to helping the grass sward tiller out.

The pull test

Pull the grass leaves by hand as if to mimic a grazing animal. If the leaves break off, the sward is ready for a grazing. If pulling results in the plants and roots coming out in the soil, then the sward needs more time to anchor fully.

12. Graze frequently at low covers to help tillering of new sward

Frequent grazing of the new sward will help the sward tiller and result in a denser sward the following season.

Ideally avoid cutting for silage in the first year if possible.

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