Noel Mackenzie: How to spend less on drainage

Drainage and irrigation both depend on a few similar phenomena such as gravity, hydraulic laws, the behaviour of water molecules and so on. The one area that is very critical to both these subjects and can be modified and managed in a sport’s turf situation is infiltration of water into the soil. Infiltration is the passage of water into the surface of the soil under the pull of gravity. Once in the soil the further movement of water downwards under the influence of gravity is referred to as percolation.

One of the more frequently misused terms in sport’s turf management is drainage. So often standing water is seen and someone says: ‘We have a drainage problem – let’s install drainage!’ They may have a drainage problem … or they may not! Standing water does not immediately mean that there is a problem with drainage and is not necessarily a reason to empty the club’s coffers to pay for pipes to go in the ground. Technically, poor drainage can result from:

• A high water table within the soil, leaving water ‘backed up’ to the surface or close to it

• A heavy soil through which percolation is slow

• A soil where water movement is held up by some physical barrier such as a ‘pan’.

Any one of these will impede drainage and leave the ground soggy underfoot, rendering the grass or other vegetation unable to grow optimally.

What has infiltration got to do with drainage?

Soils with high sand content or good structure usually have good drainage. However, if those soils are trampled and compacted at the surface, water may not go through them well, but they are still soils with good drainage because they are capable of allowing water to move away under gravity at depth – it is just that they have been damaged. In such a situation surface water accumulation is due to impeded infiltration.

Therefore, when someone sees the puddle, and wants to install drainage, they may be talking a club into a big bill running into tens or even hundreds of thousands of pounds when there is no drainage issue at all! In mis-diagnosed situations the benefits of installing an expensive and extensive drainage system may be barely determinable, indeed there can be negative impacts. It may be the case that the greenkeeper has all the necessary equipment in his arsenal to cure the problem in no time at all and at no extra cost.

What has infiltration got to do with irrigation?

Clearly irrigation involves applying water onto the playing surface which then, in an ideal world, infiltrates into the soil and percolates down to the grass roots. An ideal system would apply water evenly over the surface to enable homogeneous water contents within the soil so that putting uniformity and grass condition were consistent too. But we often see puddles on turf after irrigation (natural or man-made) so perhaps we can assume that infiltration is not uniform, even on flat surfaces. Perhaps there is more to this infiltration subject than first meets the eye? If water accumulates in certain areas then infiltration is not going to be the same over the whole surface and this implies that the turf does not receive the same amount of water as a neighbouring area. Consequently, there will be a loss of putting surface consistency and more unhappy members / players.

How infiltration works is very complex. Water landing on the turf is pulled by the downward force of gravity. This pulls the water through the turf onto the thatch that exists above the soil or the soil surface itself. Water molecules have to achieve contact with the soil particles and pore spaces between them in order to wet the surface – only then can infiltration can take place. This might sound obvious but we must remember that water droplets develop a skin like meniscus and this surface tension to the droplet can be difficult to overcome – hence why on thatchy turf it is often possible to see a silvery layer of air trapped under the water.

Once water has achieved contact with the soil, infiltration can occur but the rate will be contingent on factors such as:

• thatch and organic matter content at the surface

• sward density

• soil type and pore sizes – heavy clay and silt rich soils have smaller pore spaces in comparison to sandy rootzones

• the presence of water repellent (hydrophobic) factors such as waxy residues from fungal activity

• damage to the soil structure, such as soil compaction.

These factors ensure that water does not infiltrate or percolate uniformly. What tends to occur is that the water takes the path of least resistance and so ‘fingers’ of water movement tend to occur within the soil. In soils with impediment to infiltration and percolation due to any of the factors listed above, the fingers become more widely spaced and in the worst case scenario water may not penetrate at all and run-off sideways across a surface to an area where it can descend through the soil under gravity. Or it may become standing water in a low lying area.

In very free draining soils with minimal organic matter content the entry of water into the soil is more uniform than in loamy and heavy soils. However, even here there are spatial variations over the area and some water channels or fingers arise in the soil. In finer and less well-drained soils the fingers are less frequent, constrained in size and sometimes non-existent.

Impingement of infiltration and percolation is common in most sport’s turf settings. Usually the situation is worse the more traffic passes over an area because it reduces the size of pore spaces and causes the natural crumb structure of the soil to be replaced by large ‘plates’ that ‘cap’ the surface. Thatchy turf will also impede water infiltration because the material tends to be hydrophobic when it has dried out and, if present in sufficient amounts, holds water like a sponge above the soil in much the same way as a bathroom sponge holds water even though you might have lifted it clear of the bath.

The implications for sport’s turf surfaces are staggering. Common sense dictates that good infiltration equates to efficient irrigation water penetration into the soil and healthier turf as a consequence. From a drainage perspective poor infiltration means that surface water will more likely be present and this may close facilities or compromise playing quality dramatically, for example reduce putting speed and uniformity. From a technical turf management perspective, poor infiltration creates difficulties such as increasing the risk of certain diseases, for example anthracnose on meadow grass, encouraging thatch build-up, limiting oxygen presence within the soil profile thus causing rooting problems and reducing plant health and condition. From a practical turf management perspective the maintenance of surfaces can be impinged as the travel of mowers or other equipment causes damage to surface levels on the soft water logged surfaces and the turf is less able to withstand wear under such conditions.

Fortunately the modern greenkeeper has an arsenal of tools to maintain soil infiltration and percolation. The most frequently applied is the ‘spiker’. Technical advances in aeration machinery in recent years is staggering and many different types of tines can be applied to ensure soil structure is maintained and that water can contact the soil surface. Thatch reduction tools are also important, as is the regular topdressing of surfaces, both techniques helping to ensure that water quickly contacts the soil particles. Greenkeepers also have ‘wetting agents’ to aid water penetration through the soil by weakening the surface tension of the water in much the same way as washing up liquid does. By applying all these techniques the greenkeeper seeks to make the most of what his environment has to offer. Spiking takes place not to annoy the golfer when the greens are good but to ensure that the greens are as good as they can be throughout the year.

To summarise, whether considering drainage or irrigation there can be no doubt that the ability of water to penetrate the soil surface is fundamentally important. If water does not infiltrate well irrigation water is wasted and turf quality declines. Good, well-designed irrigation systems with accurate and even water coverage should aid the situation and avoid creating excessively wet areas that will be more prone to soil damage.

Drainage systems can reduce a deeper drainage problem within the soil to prevent soils being wet at the surface and help to reduce conditions that impact on infiltration. However, good drainage demands good infiltration, so if you have problems with standing water try to understand what is happening on your course. Clubs and proprietors should be mindful to watch for standing water and yet not hit the panic button if it occurs. What may seem to require a £50,000 drainage system may, in fact, simply require a bit of spiking and soil management.