What is it?
This is the application, and usually incorporation, of a bulky material to an area.
What does it do?
The main reason for applying top-dressing is to maintain and improve the evenness of the playing surface.
Some other reasons can include :
- To improve the moisture holding capacity of the rootzone : This is when organic matter and/or finer soil particles are included in the mixture.
- To improve surface drainage and aeration when sandy soils are applied.
- To add small amounts of plant nutrients to the rootzone, particularly when the applied top-dressing is derived from a well prepared compost heap. Sand can also provide small amounts of nutrients, especially micronutrients, even though it is often considered inert.
- By acting as a carrier for fertilisers and lawn sands.
- It can protect newly sown seeds and germinated seedlings from drying out, i.e. desiccation.
- It can dry and firm surfaces, particularly winter games pitches, when sand is applied to muddy areas.
- To dilute the density of any thatch layer. The top-dressing may increase the overall thatch depth, but the density will be reduced, making drainage easier and improving air circulation within the top-dressed zone.
- To protect the crown of grass plants during hot summers and improve their resistance to drought.
- To assist in the 'knitting in' of newly laid turf by top-dressing between the joins in the laid turf.
How should it be applied?
It is important to apply the top-dressing when both the material and the grass surface are dry, as this will ensure a rapid incorporation of the material around the base of the plant and into the rootzone where aeration holes have been made. This can prevent any smothering of the grass taking place, especially if a suitable application rate has been given and the top-dressing has been worked in by the use of a tru-lute, drag brush, drag mat or similar implement which will ensure an evenness of incorporation.
The top-dressing should be correctly incorporated into the existing rootzone otherwise rootbreaks and layering can occur, having a resultant detrimental effect on the playing quality of the turf. Incorporation of the top-dressing into a rootzone profile is achieved by carrying out aeration, particularly by the use of solid or hollow tines, and scarification prior to application.
Problems of incorrect application
1. Smothering of the grass plant will increase the humidity around the leaves, making it more susceptible to disease attack. The plant itself will also turn yellow if left smothered due to its inability to carry out photosynthesis : This in turn weakens the plant making it more susceptible to disease attack.
On fine turf areas it can be beneficial to allow the grass to be a few millimetres longer than the normal height of cut, to permit the top-dressing to be worked in amongst the grass blades that much easier.
For longer turf areas this should not be a problem and care will only have to be taken in ensuring a suitable application rate is given along with the material being worked in.
2. Annual meadow grass can readily take advantage of the exposed top-dressing surface and start to colonise the area. It is essential that any top-dressing operation is carried out when the grass plant is growing actively so that it will be able to quickly incorporate the material into the sward. This does not really apply on winter games pitches when the main criterion is for muddy areas to be firmed by the application of a sand top-dressing.
3. For fine turf areas the use of a sterilised top-dressing will help to eliminate the importation of weed and annual meadow grass seeds into the sward.
Types of top-dressing
The choice of top-dressing is very important to ensure the correct material is used for each particular area and facility. Where a suitable rootzone material already exists, it is especially important to ensure consistency of material is applied. It is also advisable to have a suitable soil analysis of the material prior to purchase and application.
Examples of typical top-dressing materials for turf areas :
Bowling / Golf greens / Ornamental lawns : Sandy soil with the main sand particles being in the range 0.250 - 0.500 mm. These types of sandy soils are sometimes referred to as being "70/30" or "80/20": This is an expression of the amount of sand mixed with a soil, although it is technically quite meaningless as no indication of the nature of the soil or the overall particle size breakdown is given.
Football pitch : Sand or sandy soil with the main sand particles being in the range 0.125 - 0.500 mm. (This size helps to give the necessary grip, or traction, required by footballers, whilst at the same time, providing for adequate permeability).
Cricket square : Clay loam with a clay content of ~ 28 - 32%.
Tennis court : Clay loam, with a clay content of ~ 25%.