This article aims to explore some of the reasons why a sandy soil/rootzone may fail to drain effectively. It draws on the agronomic experiences and observations over a number of years, coupled with some basic scientific principles.
By Steve Gingell, STRI Area Manager for the South West
Layered profile on bowls green
The nett result of holding water is often an accumulation of organic matter and invasion of undesirable grasses
T
he difficulties with layering in sandy profiles are discussed, as well as the broad concept of critical tension and
problems related to particle size and pore space. Generally, this article is aimed at fine turf but the principles could be easily applied to winter sports and any sport that is developed on sandy soils.
Layering in sandy profiles
In the ideal world a soil profile would have a uniform and evenly textured content without significant abrupt variances in soil types. However, in practice, changes in topdressing, due to cutting costs or changes in management practices can lead to an accumulation of layers.
It is not uncommon to see USGA type constructions of the 1990s where a medium-coarse sand was used in the construction, but with a medium-fine or even finer topdressing used during subsequent maintenance practices. The result can be poor performance. The difficulty of having different layers 52
of sand is that any layer of finer sand over another type will, invariably, tend to hold water. This is due to critical tension (discussed later). Once the depth of accumulation reaches that of the critical tension of the sandy topdressing then, all other aspects being equal, the sand will drain. This could, however, be in excess of 300mm for medium-fine sands. The nett result of the holding of water is often an accumulation of organic matter and, ultimately, invasion of undesirable grasses leading to soft, wet surfaces. Ideally, the layer should be removed but this is often not possible and would be disruptive to play. The first step to take is to reduce the
organic matter build up ensuring removal rates are higher than accumulation. This involves a whole range of management treatments of the surface from hollow coring to fertiliser application. The presence of organic matter can also slow drainage rates, particularly if not fully broken down. This organic sponge is regularly seen in the top 15-
50mm of a fine turf surface and needs removal as described above. Where fungal breakdown of the organic material may occur it can also lead to waxy coatings of the sand grains, making them hydrophobic. This results in the classic dry patch condition. Modern wetting agents and wax removal agents can make a significant difference to the water percolation ability of a hydrophobic rootzone.
It is vital, however, to continue to use
appropriate sandy dressing unless there are other specific issues such as supply, chemical analysis or reliability issues as the gradual build up will eventually help drainage rates. Regular hollow coring and possible deep aeration with topdressing backfill to slowly ameliorate through previous layers will also assist in the process. Future changes in dressing need to be
carefully planned. It is vital that not only any sand/ameliorant ratio is examined but also the sand particle size distribution. Recommendations by your agronomist should be made following a
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