John Reynolds looks at the benefits of linear decompaction and aeration on clay soils…


FEETofCLAY


WHEN Terry Pritchett wrote his best selling novel Feet of Clay he certainly wasn’t thinking of Football or Rugby pitches in the UK that's for sure! However, the title would have been particularly appropriate to our industry, as thousands of Course Managers, Green Keepers, Groundsmen and players can testify.


Many of our winter sports pitches, and golf courses too for that matter, are constructed on clay soils which are very susceptible to soil compaction. This can present particular problems when it comes to drainage throughout the playing season and also when it comes to end of season renovation work. Clay soil is regarded as inherently


problematical by most turf managers - wet, soggy and often unplayable in winter - rock hard and unforgiving as a playing surface in summer.


Soil is a combination of varying sized particles, consisting of sand, silt, clay, minerals and organic matter. Air and water are retained and circulated within the air pockets between soil particles known as ‘pore space’. In ideal conditions the ratio of air to soil particles would be 50:50. The reality of course is very different, especially in soils supporting sports turf. Clay is the smallest of the present soil particles, with 1,000 times the surface area in a given volume of soil when compared with larger sandy soil particles. What this means, is that clay packs


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together tightly under pressure of play and binds water within the soil profile by surface tension preventing water percolation and drainage. If the clay content is more than 30- 40%, it would be considered as heavy clay with the typical sticky and smeared gluey characteristics we all witness every winter on heavily used areas of sports turf. Clay tends to swell when wet and if compacted will remain saturated, cold and undrained for long periods. As a result the soil will freeze to considerable depths in cold winters, causing root damage and suppressing beneficial microbial activity long after sandy soils have dried out and warmed enough to create good growing conditions. As spring arrives, water evaporates slowly, preventing early recovery from the ravages of hard winter play. The following summer sunshine rapidly converts compacted clay soils into ‘concrete’, preventing penetration of roots and also moisture from rainwater or by irrigation due to ‘run off ’. In these conditions, newly sown grass plants will burn off rapidly, leaving bare cracked areas for weed invasion and presenting poor playing surfaces for the new season. Establishing whether you have clay soil or not is very easy; first take a handful of soil and gently squeeze it, clay soil is sticky and plastic-like and will roll into a fairly solid ball readily without breaking up, whereas sandy soil will crumble easily. Rubbing the soil gently between


your fingers will also create a polished finish to the clay.


Not that clay is all bad news - clay soils


are usually very rich in nutrients and established grass generally survives drought periods far better than on lighter soils.


CHOICE of machinery to relieve compaction, and for use during renovation, is critical with clay soils, as is timing. The use of heavy machinery should be avoided at all costs especially in wet conditions. Any machine using tines is potentially damaging to clay soils and should be used with caution. There are some excellent high speed and very efficient tined products on the market from Weidemann and Redexim - Charterhouse with their latest Verti-Drain models. The very promising Gwazae Ground Probe system from Keith Kensett, which uses compressed air is very fast and effective. Problem is, they all have limitations when operating in clay.


Let me explain the rationale behind this statement with the following case history: Recently I was asked to visit a well- known rugby club near Bristol where the pitch had been virtually unplayable for almost two months. Next-door was an equally established football club with the same problem. The Groundsman explained that despite “applying 50 tonnes of silica sand for seven years, in


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