0 Managing saturated soils

2014 is set to be England's hottest in over 350 years, However, there is no doubt that the higher than average temperatures have been a factor in the heavy rains many areas have experienced.

November started with ten days of cold but reasonably sunny weather, but it will long be remembered for the floods during its fourth week. It may be hard to recall that until, 19 November, it was generally rather dry, but then the heavens opened, as slow moving and intense low pressure systems arrived and brought prolonged bouts of heavy rain falling on rapidly saturated ground.

Average rainfall in November, across England and Wales was 134mm of rain, which is 128% of the mean.

All this wet weather, with more likely to come, does not bode well for groundsmen looking after soil-based sports pitches during the winter months. We have already seen a number of football and rugby clubs at local level postponing matches due to saturated pitches.

In a lot of cases, many of these postponements could be prevented if clubs were to invest more money into their pitches, both during the construction phase and post construction, by having a robust maintenance regime in place. However, for many natural soil-based pitches it is more about the lack of maintenance and understanding about the type of pitches being managed. Understanding your soils, and how to manage them, will go a long way to producing a decent playing surface.

Some of the benefits of a having uniform soil texture and good soil structure are:-

• High drainage rates
• Increased root development
• Surface able to withstand wear
• Positive air circulation - healthy microbial population
• Reduced incidence of disease
• Drier surface

Knowledge and understanding of soil physical properties has always been important for professional turf managers, when making decisions about maintenance operations and when carrying out reconstruction works. Precise soil knowledge, including information on boundaries between soil types, should result in more efficient use of fertilisers, pesticides and improved management practices, thus ensuring that the final managed outputs result in the production of economically safe, consistent, playable natural sports turf surfaces.

Soils can vary in many ways, both physically and chemically, on a local or regional scale. Many factors, including original parent material source, climate, weathering processes, topography or history of the land use influence their properties.

This soil variability gives rise to all the different types, universally classified by soil texture composition. Soil composition (soil texture) is determined predominantly by mineral particles and organic matter content and can be classified by the percentage of sand, silt and clay mineral particle content.

The Soil Texture Triangle, as shown on the image, helps us classify the soil type, these percentages are determined by undertaking a PSD, particle size distribution analysis.

The definition of soil texture is the relative proportion of sand, silt or clay in a soil.The terms sand, silt, and clay refer to relative sizes of the soil particles - sand, being the larger soil particle, feels gritty; silt, being moderate in size, has a smooth or soapy texture; clay, being the smaller size feels sticky. Soil particles are illustrated in the table.

Soil particles are distinguished by their size. Most soils contain a mixture of different soil particles. The particles and the soil's structure determine the pore spaces. A soil with a high proportion of coarse sand will contain large pore spaces and drain quickly, whereas a soil having finer sand, silt or clay particles will contain smaller pore spaces, and therefore will drain more slowly.

particle sizes

The quantities of large and small pore spaces directly affect plant growth. On fine-texture, clay and/or compacted soils, a lack of large pore spaces restricts water and air infiltration and movement, thus limiting root growth and the activity of beneficial soil organisms. On sandy soils, the lack of small pore space limits the soil's ability to hold water and nutrients.

The strength and permeability of any soil is determined by its structure, soil type, drainage capacity and how well it is managed. Soils will perform differently, governed by the amount of water, root mass and air there is in the soil matrix.

There are three descriptive classifications (Saturation, Field Capacity, Permanent Wilting Point) that can affect the performance of the soil matrix and the way grass grows in the soil.

When saturated, a soil is said to be at its maximum retentive capacity; that is, all soil pores are filled with water. Saturation usually occurs for short periods of time, either during heavy rainfall events or when soil is being irrigated.

Field capacity (F.C.) is the amount of water that is held in soil after it has been fully wetted and all gravitational water has been drained away. At field capacity, the soil holds the maximum amount of water that can be stored and can be used by plants.

Permanent wilting point (P.W.P.) is defined as the minimum soil moisture at which a plant wilts and can no longer recover its turgidity.

Available Soil Moisture is the amount of water held between F.C. and P.W.P. It is a measure of the amount of water in the soil that is "potentially" available to plants.

Understanding, and knowing how to manage your soils when they are in a given state, such as Saturated, at Field Capacity or indeed at PWC, will ensure you are in a better position to maintain good grass cover.

Saturation Field Capacity Permanent Wilting Point

saturation

Firstly, we need to understand what problems are facing groundsmen when pitches become flooded and remain saturated for long periods of time. Once a pitch becomes saturated, that is to say all the pore (air) spaces in the soil profile remain filled with water, then we are in a situation of the pitch being in a poor state and will be prone to damage.

The spaces between the particles of solid material are just as important to the nature of soil, as are the solids. It is in these pore spaces that air and water circulate, and help provide the plant with the necessary nutrients it requires to respire and grow. These pore spaces can vary in size and are generally classified into two sizes - macro pores (larger than 0.08mm - 80 microns) and micro pores (less than 0.08mm - 80 microns ).

Macro pores generally allow movement of air and the drainage of water, and are large enough to accommodate plant roots and micro-organisms found in the soil. The ability to retain a good balance of macro pores in soil structure is essential for maintaining grass plant health. It is when these macro pores are either reduced in size by compaction or filled with water (saturated) that we see deterioration in pitch playability and resistance to wear.

However, the main contributing factor that reduces and damages pore spaces in soil is compaction, caused by compression forces, normally associated with play and use of machinery, particularly during wet weather periods. Over time, these compression forces reduce the pore spaces so that air, water and nutrient flow through the soil profile is restricted, and leads to many problems associated with compaction.

There are two distinct types of problems on winter games surfaces; one is compaction by treading (30-60mm depth) and the other by smearing and kneading (30mm depth) when playing in the rain and on bare soil surfaces.

The heavier the soil the longer it will take for the pitch to dry out; sandy soils are more free draining than heavy loam or clay soils and, therefore, will dry out more quickly.

Bromsgrove DrainageHaving an effective pitch drainage scheme will help. Most modern pitches tend to have primary and secondary drainage systems installed. These systems aid the removal of surface water quickly and tend to keep the pitches playable in periods of wet weather.

However, the effectiveness of any drainage system can be compromised over time when the drain runs become capped; it is important to retain a link between the drains and the playing surface.

This will be achieved by regular aeration work and the application of topdressing. Ideally, clubs should be putting on at least 40-60 tonnes of sand per pitch each year. This not only keeps the playing surface free draining, but also helps to restore levels.

Playing on saturated pitches will bring disastrous results. It is often better to postpone a fixture rather than ruin the playing surface for the rest of the season. Scrummage and line out play are the main causes of damage on rugby pitches during wet weather periods. The severity of the damage will be dependent upon the soil type and the ability of the top 100mm to drain quickly.

It is important that, once the game has finished, remedial work is carried out to repair divots and stand the grass back up. Care should be taken not to further damage the pitch by trying to get machinery on when it is wet and saturated.

A rubber rake can be used to help stand the grass back up in localised wet muddy areas; if left buried, the grass will soon die. Once this has been completed, the use of harrows/brushes can be used to stand up the sward. This is often followed by rolling back the surface using a mower or, better still, a SISIS Quadraplay unit or similar type of equipment.

Undertaking a regular aeration programme will go a long way to ensuring your pitch is able to cope during wet conditions.

Gay-Hill-Aeration-day-Oct-09-103_website.jpg

When do we aerate?

Aeration should be carried out on a regular basis when weather and soil conditions allow. You may contribute to surface deterioration if you aerate during bad weather when the surface is saturated and likely to smear; timing is the key to successful aeration.

There is a wide range of professional aerators for use on winter turf pitches, available as walk-behind, ride-on, trailed or tractor mounted.

To alleviate these compacted layers, we need to consider a range of different techniques and equipment that can encompass the different types of playing surfaces (fine turf and field turf facilities). The main aim of aeration is to penetrate the soil profile to create new macro pore space. This is achieved by several methods:

• Solid tines - hand forks, pedestrian and tractor mounted vertical punch aerators
• Hollow/coring tines that remove soil cores from the soil
• Flat/star tines
• Disc/blade implements (linear aerators). A number of new machines on the market are designed to open up the ground and back fill with permeable materials
• Compressed air and water injection aerator systems
• Drill and fill techniques

It is essential to use a variety of aeration techniques to prevent pan layers being created. This usually happens if you continue to use the same aeration technique set at the same depth, resulting in a compacted layer forming at the base of the tine or core depth. Most turfgrass managers will, therefore, vary the methods of aeration by changing the depths, size and diameter of tines.

The variety and choice of implements and devices now available is excellent, providing different tine sizes, operating widths and shattering features that can meet the requirements of any facility and, more importantly, do not disturb the playing surface, allowing play to continue after use.

terrain aeration dudleyWith the demand for higher quality, all year round playing surfaces, turfgrass managers are always interested in trying out new techniques to keep playing surfaces aerated. In recent years, we have seen the development of high pressure air and water aerators that offer deeper aeration than conventional aerators.

Depending on the condition of the soil, you should be aerating on a monthly basis, trying to aerate to a depth between 100-200mm.

Once a year you should aim to aerate to a greater depth (200-300mm) using a larger, more powerful aerator. This will help dramatically, especially if you can topdress the pitch immediately afterwards with sand, enabling this material to go down into the aeration holes.

One of the most popular pitch management tools is the Sisis Quadraplay. The Sisis Combination Implement Frames make up a single pass maintenance system which incorporates a mounted frame. The mounted frame accepts a variety of different implements for use on both turf and hard porous surfaces.

Implements such as grooming rakes, spikers, slitters, rollers and brushes can be added to the frame, making this an exceptionally versatile piece of equipment. It can be used for fine and outfield turf to perform a range of tasks so effectively that you can aerate, brush, spring tine and roll in one pass.

Using these frames before and after matches helps keep the pitch in good condition and, above all, the spiker ensures the pitch is regularly aerated. The presentation of the pitch is important. If it looks tidy and well presented, with bands and stripes, it often inspires the players to perform and, more importantly, gives them a safe, consistent surface.

forking rugbyUnfortunately, I see far too many club pitches that become unplayable or prone to damage, mainly due to the lack of basic maintenance being carried out.

Regular aeration, particularly on training pitches, will help enormously; there is nothing worse than having to play or train on a wet, soggy pitch.

The extent of compaction is also dependent on the soil type. Clay, clay loam, silt and sandy soils will all compact, but the majority of compaction problems are associated with the heavier soils (clay and clay loams).

There are a number of methods available to measure soil compaction/hardness and infiltration rates.

These include:

• Cone penetrometers - devices that are pushed into the ground, measuring the resistance of the soil when inserting
• Taking soil samples using density rings to measure soil bulk density
• Clegg hammers that measure the impact of a weight dropped from a predetermined height
• Changes in visual appearance, performance and physical properties of the soil and surface
• Infiltration rings - can be used to measure the infiltration rate of the soils/rootzone profile - decreased water infiltration and reduced hydraulic conductivity through the profile will lead to surface waterlogging, ponding and the possibility of the soil profile remaining in a saturated state until it is able to drain

Having a saturated soil reduces soil strength, which often results in loss of groundcover and can, eventually, lead to a loss of fixtures. Once grass cover is lost, the surface is more susceptible to weed invasion. The most common weeds seen on community winter sports pitches are daisies (Bellis perennis), Dandelions (Taraxacum officinal) and Greater Plantain (Plantago major), the latter being a good early indicator of compaction problems.

Compacted or sealed surfaces can also promote anaerobic soil conditions that, once formed, reduce root growth and restrict microbial activity.

The above conditions will adversely affect a surface's performance in many ways, such as ball bounce, ball roll, reduced ball speed, player welfare and, in the long term, damage the soil structure, which may lead to expensive reconstruction costs.

So, what are the other benefits from carrying out aeration?

• Improves soil surface drainage (water infiltration)
• Helps to increase soil temperatures
• Increases soil pore space - allows gaseous exchanges in the soil (oxygen in, carbon dioxide out) that improves root growth and development
• Aids integration of topdressings into the soil profile
• Aids the breakdown of thatch/organic matter
• Promotes better surface levels that will increase ball roll /speed
• Aids surface firmness/dryness, thereby increasing ball bounce and surface grip

Without effective aeration programmes, pitches would return to the quagmires of days gone by. Using a variety of aeration techniques and machines, modern day pitches can remain playable year round.

MarbleHill FootballPitchIt goes without saying that aeration plays an important role in the management of natural turf playing surfaces and should be a key operation to aid turf grass performance, but be mindful what technique or machine you choose to use on your playing surface.

It is also important to note that damage can occur to the playing surface if the wrong type of equipment is used or the operation is carried out in the wrong conditions. Dig trial pits or take soil samples to ascertain the type of soil you are dealing with before using a large and fast operating aerator; these powerful machines are capable of doing a lot of damage in the wrong hands.

It's not just a case of 'running over the ground as fast as you can'. There's much to consider when aerating - soil type, speed of the machine, tine spacing, depth of operation and, importantly, what you are trying to achieve, all need to be considered.

Be aware of the health and safety considerations when operating aeration equipment. Do not attempt to adjust the machine when it is working, ensure you switch off the machine and any primary mover when undertaking any adjustment or repairs.

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