Shade seminar findings at Twickenham
By David Saltman
This was the second conference that I have attended this year on shade problems associated with Stadium environments.
The first was held courtesy of PSD (NW) Ltd at the Reebok stadium back in March and showed the effects of shade on grass growth and some of the possible solutions to the problems. We have already seen the advent of moving pitches in Japan, Holland and Germany, and there is even talk of lifting pitches hydraulically to the roof of the stadium to provide the necessary light for growth and in effect creating an indoor arena during non match days. The Millennium stadium's turf tray system allows the turf modules to be moved in and out of the stadium on fork lifts. Greentech have developed a similar successful system of interlocking turf modules that are very portable. There is also research on going using huge mirrors on stand roofs that will follow the sun movement and deflect direct sunlight onto the shaded areas of the ground.
This seminar arranged by Greentech cemented our views of the difficulties involved and it was interesting to hear the views, research and findings of our American counterparts who are also trying to resolve this ever increasing problem.
The day started with an introduction from Keith Kent in his newly appointed role as Grounds Manager at Twickenham RFU and Simon Jacob, the ex-West Ham Head Groundsman, now the UK Technical Director for Greentech.
Seminar proceedings kicked off with Dr Martyn Jones talking about Climate and Turfgrass Management.
Many facts and figures were related to the audience about the varying weather patterns that we face in different areas of the UK. On a general note, the fact that our winters are cool and wet in Britain but that the average rainfall will differ considerably from the North West to the South East of the country. The NW, in particular, is wetter than the rest of the UK with an average rainfall of more than 100mm per month.
The North of Scotland receives around 1208mm precipitation a year, whereas the east of the country receives less than half this average at around 600mm per year.
Dr Jones continued saying that in Lancashire, on open field sites, 'field capacity' (waterlogged state) was generally reached by October and remained at field capacity or wetter, in a state of ready compaction, until the following April. By contrast, in Norfolk, field capacity was only reached in January and remained until March.
As the ground was only considered to be in a 'dry' workable state in Lancashire for five months of the year there were obvious difficulties arising for turf management.
Purely from a wear factor the areas further north have to cope with far more problems.
These wet days during the growing season lead to very favourable growing and germination conditions for poa annua above other cool climate grasses. Therefore the drier areas of the country noticed far less germination of poa because of the improved soil conditions.
In Lancashire, there are, on average, less than five days subject to drought in a year. In Dyfed Wales, 70% of the year is deemed as 'ground at field capacity' (water logged).
So, the potential germination days for poa in the North West, is 240 days a year compared to just 110 days in Norfolk.
Because of these conditions, the ability to aerate mechanically to compensate against water compaction is greatly minimised because of general soil conditions.
Dr Jones then went on to talk about particle size distribution in soils and root zones and their water conductivity in relation to drainage rates. The largest pores found are called Macropores and are usually found in a soil or sand based mix of even sized particles. Macropores offer large air space or voids between the particles, which allow for quick drainage (conductivity).
In unevenly mixed particle sized soils/root zones, Micropores are found. These are much smaller air spaces, which offer a far greater surface area to hold onto water molecules slowing down the conductivity of water (drainage).
A soil or root zone with a Micropore structure will hold water against the force of gravity and create a medium that will hold water back from draining away. The use of finer sands in construction or the build up of organic matter will help to form this type of soil structure.
He talked about the properties of single sized sands and how their use can be combined effectively with the depth of construction as outlined below. In other words, the finer the sand used the deeper the construction needs to be to be able to allow water through the profile.
1, Medium sands 0.25mm-0.5mm will need a minimum construction depth of 220mm to provide good conductivity (drainage).
2, Fine sands 0.125mm-0.25mm will require 400mm depth of material.
3, Very fine sands 0.06mm-0.125mm then a minimum depth of construction to 900mm is required.
He added that evapo-transpiration doesn't vary greatly across the UK as we populate only a small island.
Science proves that if the air filled porosity in the ground is less than 10% then black layer (anaerobic conditions) occurs within 24 hours.
To ensure adequate soil aeration there must be an extensive and continuous network of Macropores so spiking and solid tining, while beneficial, are nowhere as good as maintaining a natural Macropore network in the ground.
He also said that wetting agents do not cure problems of poor soil structure. Water has moved through the planet for millions of years without the need for chemical additives. His view is that the particle size distribution needs to be correct from the start.
In the south east the problems associated with weather are different, so root zone materials need to be carefully considered. In drier conditions the surface may dry too quickly and become unstable, so there needs to be a balance for every situation.
We should be lobbying architects and employers to make them understand many of the local ground and climatic problems that we have and how we intend to resolve them.
He ended saying that, 'We shouldn't be blinkered by what we think is right. If there were no problems then we would have perfect pitches already. If we are passionate about natural grass then we have to fight to keep ahead of the synthetics-otherwise we could lose our grass playing surfaces altogether'.
Our next speaker was Andy Newell from the STRI whose subject was the general problems of shade in stadia.
He started his speech by highlighting the fact that, over the last 100 years, stadia have gone from open venues to, in many cases, virtually indoor arenas.
The reason for this was to improve spectator safety, comfort and to get more backsides on seats!
Shade, as we are already aware, causes poor growth, grass cover loss, more stress and more incidence of leaf disease.
To compensate for poorer light levels, the plant tries to grow bigger, by swelling with water to increase its surface area. This weakens the plant considerably making it vulnerable to wear and disease.
So he asked 'Why is light important?'
Photosynthesis occurs in green plant tissues, takes carbon dioxide and water and uses natural sunlight to convert these molecules into sugars- oxygen for us to breathe is purely a welcome bi-product!
Without photosynthesis the world would be devoid of life and surrounded in a CO2 gas.
Sugars are used to create starch, which in turn provide the building blocks for the plant to grow.
Under the shade of the stand, there will only be about 20% of the natural light that you would expect to see in an open field. This light is termed diffused light, not direct sunlight.
The more days of shade in a week, the more wear intolerance there is. Each additional day compounds the plants ability to recover from wear.
Andy showed photographs of a Hemiview analysis. These were 180 degree photographs taken from varying ground positions in stadia showing a detailed map of the sky and the obstruction of light from the stands.
He used these photos to assess the effects of man made and natural objects to diffuse natural light. By looking at the sun's trajectory over the stadium at different times of the day and different times of the year, it has been possible to build up a full picture of shade pattern in a stadium.
In the case of Twickenham Rugby ground the proposed new South stand will cut out all direct light (currently available) from September through to April and will reduce by half the natural direct light in the stadium throughout the year, though it will not have a massive effect in terms of diffused light.
The new stand will reduce daily direct sunlight onto the pitch in June by four hours, from 12 hours down to eight hours. So the grass will have a third less time in peak growing season to photosynthesise.
In September the current direct light hitting the grass is found between the hours of 08:00am-2:30pm. The proposed new stand will only allow direct light onto the pitch between the hours of 11:30am and 2-30pm. This again is a significant amount of reduced light and time to photosynthesise, at a time of year when the grass is subject to games and the usual wear and tear, but about to slow down on growth and therefore recovery.
In December there are currently two hours in the middle of the day when some direct light gets on the pitch, the new stand will prevent that altogether.
Our next speaker was the first of the American duo, Dr James Crum talking about root zones for playing fields.
Dr Crum, from Michigan State University, reiterated the words of Martyn Jones talking about the three phases in soils. He stated that:
Air sits in Macropores, Water sits in Micropores, And then there are solids. Water runs more efficiently through Macropores, whereas Micropores hold water efficiently.
Native soils tend to have high levels of fines, i.e. silt and clay particles, and these fines tend to fill the Macropores, creating more surface area and the ability for cohesion between the water and soil particles.
A high sand content root zone will have a quality of rapid drainage. The problems are that there are so few Micropores that retaining water in the root zone for the plant is difficult.
So he asked, 'How much water will stay against gravity?'
As the particle sizes between two sands in the same mix increases, so do the water retention qualities. In other words large air spaces will have little cohesive quality and water molecules are gravity-pulled down through the profile. Without water there is little or no cohesion between the particles, and therefore the profile can become unstable.
He went on to say, ' what can we do to stabilise the root zone?`
We have to look closely at a number of issues, which include, particle size distribution, average particle size, particle shape and soil density (relative density).
The wider the distribution of sands the more stable a surface becomes, but stability means compaction and water retention which cause problems in itself. So we need to find a balance between providing a growing medium that allows water to drain sufficiently quickly without causing the profile to dry out causing stress to the plant and an unstable playing surface.
We are not forgetting nature's own little reinforcing rods -roots - which, apart from the other functions of nutrient and water uptake, help stop the surface disturbance during play.
We then watched a series of slides and graphs showing extensive testing of different sands and mixes of root zones, the results clearly showing that, by adding 10% by volume of silt and clay particles to a medium, sand increased its strength by 100%.
He went on to add that the optimum water content in a soil or root zone for strength was 9%.
One of the most important points of the day was the fact that soil strength is always optimised if the original construction of the playing surface is done when dry conditions prevail.
The second of the two American speakers was Dr Trey Rogers, his seminar subject was managing turf grass under reduced light conditions.
Dr Rogers is part of a team who have for over fifteen years been carrying out experiments at the University on the physiological change to turf grasses in shade.
They have been testing cool and warm climate grasses under a 200 square metre dome, which mimics shade in stadia. The grass trays are laid out along the floor, and the first ten feet of the dome walls are blackened to stop any outside light penetration. Above this, the dome allows only diffused natural light.
Immediate results show that the plant suffers with lower carbohydrate reserves and reduced transpiration rates. The recent research focus has been on turf grass species, plant growth regulators and exogenous carbohydrate factors.
Using growth regulators on shaded turf improved photosynthesis by 40%, the reason being that the plant produces more tillering leaves or aggressive stoloniferous growth, instead of providing cell elongation (growth to you and me). He also found that the amount of regulator used could be significantly reduced after each and every previous application. (Trinexapac-ethyl was the growth regulator in question).
We are all aware of the four environmental factors required to grow grass, light, temperature, moisture and oxygen.
Given that shade slows photosynthesis, then is it possible to give the plant the sugars that it requires to make starch? The answer is yes but it has to be in the right sugar form. Much of Dr Rogers research has been on the effect of exogenous fructose applications to grass plants under reduced light conditions.
The experiments are still ongoing but so far during extensive testing, adding fructose improved the plant leaf's chances of recovery. After six weeks of adding this particular sugar there were clear improvements.
I found the seminar very enjoyable and it was well attended with around 80 delegates. I hope to bring more conclusions on the consequences of shade to you soon.