15 Straight Talking

STRI-Topdresser.jpgWith ever-rising costs, many golf clubs are looking at ways to reduce their maintenance budgets. Topdressing is a fundamental part of producing quality putting surfaces: it firms and smoothes the surface and, by building up a layer of uniform, sand-dominated material, it maintains good drainage and air exchange, which helps prevent thatch accumulation.

Regular application is advised, aiming to apply somewhere in the region of 6 x 20 tonnes on an average 18-hole course, which represents a significant cost. This article discusses the possibility of using straight sand, both for financial reasons (it is sometimes half the cost of a traditional sand/soil mix), as well as to obtain the desirable quality and consistency from your topdressing material.

Quality supply issues

Getting a consistent, suitable topdressing supply can be difficult. I have recently studied independent particle size analyses of various topdressings and rootzones for golf course clients. Many, commonly used, sand/soil topdressing mixes failed to meet industry standard guidelines. The majority failed on particle size distribution - they contained too many fine particles (fine sand, very fine sand, silt and clay). This negatively impacts on the drainage properties of the material.

One way to address a topdressing mix that fails, would be to reduce the percentage of soil in the mix, e.g. move from an 80:20 to 90:10. However, if the sand used in the mix is largely fine in particle size, and only just passes particle size/drainage criteria, then it will likely fail as soon as soil is added. In this instance, there is a case for going over to straight sand.

Particle size analysis recommendations

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There are two main industry standards used to identify suitable topdressing material - USGA specifications, as shown in the table, and more recently produced STRI standards for the UK, as shown in the grading curve. The latter have slightly lower drainage rates to reflect the differences in our climate compared to the US, i.e. less monsoon-type rainstorms and more general grey drizzle! The UK guidelines were developed following research assessing a broad range of rootzone materials/mixes.

Consider straight sand

If a fairly coarse sand, or sand/soil mix that drains well, dominates your existing rootzone/upper profile, then moving to straight sand is unlikely to be suitable. However, if you have a soil-based profile where drainage could be improved, and your existing topdressing is on the fine end of the recommended spectrum, then straight sand is, potentially, a good option.

Provided the chosen sand is of the correct particle size range (not too coarse or with too many fines, silt and clay), compatible with your existing topdressing/rootzone and incorporated correctly, then there should not be any concerns with root breaks or overly droughty surfaces. An agronomist, supported by independent laboratory testing, should ideally verify compatibility.

Important points to note before making the change:

Particle Size Analysis - It is essential that the sand is chosen carefully, verified by laboratory testing to determine its particle size analysis. The STRI would be happy to check the suitability of sand for use.

Compatibility - If possible, it would be best to use the same sand as found in your existing topdressing. You could ask your supplier to drop the soil content so as to reduce the quantity of fine particles. The resultant material should be analysed for particle size distribution to check its suitability.

StellaRixon-STRI.jpgConsistent Use - Once the change to sand has been made, do not go back to using a sand/soil mix, otherwise drainage and root break problems could occur.

If it is felt that more nutrient/moisture holding potential is required, then perhaps apply inorganic, diatomaceous earth ceramics such as Profile, Axis or Isolite CG. These need to be applied at a generous rate, e.g. 300g/m2 once a year. Alternatively, try seaweed meal at 75-100g/m2 once or twice a year.

Integrate old with new - Ensure that the new material is well integrated with the existing rootzone. The surface should be regularly aerated to work the new material into the soil profile to avoid creating a layer at the surface. Regular light sand dressings would be best, rather than one or two heavy dressings, as this may increase the risk of layering.

Further advice - The STRI's agronomy team would be happy to give more advice specific to your site. STRI Laboratory Services are available for particle size analysis and other soil testing services. Contact: 01274 565131.
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