Case study - The development of new natural turf facilities within the Chelsea FC training complex at Cobham

Background

TGMS is retained by Chelsea FC to provide ongoing agronomic support for the pitch at Stamford Bridge and the extensive training facilities at Cobham. This role not only involves providing technical support to the Groundstaff in respect to ongoing maintenance, but has involved a significant design input into the pitch reconstruction carried out over the summer (2005) at Stamford Bridge and the construction of a new phase of natural turf pitches at Cobham.  The work at Cobham has presented some opportunities to develop, in conjunction with the Head Groundsman Mr Jason Griffin, an approach to training ground construction that might improve the long term cost-effectiveness of turf maintenance within a training ground setting.


In the search for the ultimate natural turf playing surface there has been a deliberate focus on the need for highly efficient drainage. The result has been the creation of pitches that are based on rootzones with very high sand contents. The vast majority of higher profile stadia and training ground pitches are constructed using rootzones with sand contents in the order of 90 – 95 % and drainage rates in excess of 100 mm of water per hour. Generally, these constructions are providing free-draining playing surfaces that cope admirably with even the highest rainfall events. However the effect of high sand content rootzones on turf management is considerable. Efficient turf grass growth is reliant upon a balance between the provision of adequate supplies of light, water, air and nutrients. Maintaining a balanced supply of the latter 3 elements is affected directly by the nature of the pitch construction. It is the provision of adequate nutrition that is particularly problematic in high sand content pitches. There are three main issues that affect nutrient supply in sand rootzones;

• silica sands are inherently low in nutrients due to the mineral composition of the sand sized particles themselves and a lack of organic matter (the main source of nutrients in natural soils) occurring naturally in quarried sand products;

• nutrients applied through fertilisation are readily leached out of the rootzone because of the high drainage rate of the medium and the lack of any useful nutrient holding capacity associated with silica sand;

• silica sand based rootzones have lower microbial populations than natural soils. Many of these micro-organisms perform numerous critical functions in the soil that affect nutrient availability and supply to the grass root system. The net result is that Groundstaff must apply fertilisers at a high frequency in order to maintain sufficient turf growth and adequate colour. It is not unusual for turf managers to apply products once every 2 weeks or so during periods of peak demand. Turf grown on sand-based rootzones is often prone to disease, which is frequently linked to nutrition, either due to over-application, under application or just the presence of an unhealthy, weakly-rooted turf.

We seem to have forgotten the basics of sound plant husbandry.  Is anyone questioning the need for ultra-free draining pitches at the expense of all the benefits of natural soil?  Is it not possible to utilise the beneficial attributes of what nature has to offer on a site rather than imposing artificial, demanding restrictions on plant health and vigour?

Science and Nature

The new phase of pitch development at Chelsea’s training ground at Cobham was approached with an open mind about pitch construction. The first objective was to carry out a thorough examination of the existing site in order to evaluate the potential to use the indigenous soil. The site was scanned using TGMS's unique EMI soil variation mapping system, whilst simultaneously mapping the site for boundaries and levels (please see Figures below; results of the EMI scan on the left, topographic survey on the right).       

 

After the initial EMI scan, soil samples were selected from different parts of the site to quantify the variation shown on the scan image. The differences shown in the scan were reflected in the texture results; "yellowier" coloured areas comprised a sand content of 80%, whilst "browner" coloured areas comprised a sand content of 50%.  Generally, however, the site comprised naturally free-draining sandy loam soils with the potential to be developed without the need to import vast quantities of additional sand and gravel.

The chemical analysis of the soil showed that the soil has an acid pH in the order of 5.5. This needs to be increased by one unit in order to create conditions optimal for healthy perennial ryegrass growth. The levels of the main plant nutrients; potassium and phosphate were also on the low side, requiring some attention.

The site had been used as a college sports field for some time prior to acquisition by Chelsea FC, but the turf had become run-down and weedy and surface levels were poor. There were no reported drainage problems during this period and, therefore, a decision was taken to up-grade the site using the existing soil and rely on the natural drainage properties of the site rather than installing a potentially unnecessary drainage system. The pitches would be monitored during the first year of use to assess the requirement for drainage at a later stage.

A decision was taken to develop the site by tackling the following issues:

the nutritional and structural qualities of the soil would be improved by incorporating re-cycled green organic waste compost during cultivations. This organic matter would also improve soil structural resilience, so reducing the likelihood of severe compaction and maintaining good drainage rates;
lime would also be incorporated to raise the pH of the soil by 1 unit from 5.5 up to 6.5;
the field would be levelled within the existing grade of the land to remove the minor surface level imperfections (humps and hollows);
an automatic irrigation system would be installed;
the pitches would be seeded with a high quality perennial rye grass seed mix in line with the main stadium pitch and the other 3 phases on the site.

A detailed specification of work was prepared by TGMS and sent out to tender.  The contract was awarded to Speedcut Contractors Limited, based in Oxfordshire. 

   

This project to develop the latest phase of the training ground at Cobham has demonstrated that it is possible to utilise a natural soil providing that a thorough scientific examination of the site is conducted and the natural properties of the soil are enhanced appropriately. This will provide the basis for pitches that are more sustainable in respect to nutrient management and water management and that still provide first class surfaces for football. To achieve this, however, the role of the Groundstaff is vital. 

The role of the Groundstaff

Once the basic building blocks of correct soil moisture, structure and nutritional properties are in place, the preparation of the highest quality turf surface is completely reliant on the skill, expertise and hard work of the Groundstaff. The difficulties of this task are exemplified at Chelsea where the Groundstaff have to manage 5 different pitch construction types, all with differing requirements:

• The stadium pitch based on a high sand content rootzone with gravel raft and significant shade problems created by the stands.
• Phase 1 of the training ground (2-3 pitches), based on the same profile as Stamford Bridge.
• Phase 2 (2-3 pitches), based on a sand rootzone but without a gravel raft.
• Phase 3 (3 pitches), based on the natural soil but with a supplementary sand slit surface drainage system.
• Phase 4 (7 pitches) based on the natural soil profile.

The range of construction types and the differing environmental factors between locations means that each phase has different fertiliser and irrigation requirements. The job of controlling these variables, and at the same time preparing a surface to the very highest visual and playing quality, is down to Jason Griffin and his team at Chelsea.  The modern Groundsman is a true professional, with responsibility for managing and training a skilled workforce, keeping abreast of all the latest innovations and developments, managing a significant budget, communicating with high level management, organising the team to prepare in excess of 10 hectares of turf to the highest standards, the list is exhaustive. As sports turf consultants, we play a role in assisting with the technical requirements of managing such a complex range of turf environments, but this is just one cog in the extremely demanding life of the modern turf manager.

Into the future

The site at Cobham offers a unique opportunity to compare the performance of different construction types under similar levels of use. With sustainability becoming a key issue in respect to use of chemicals and water, the data sets gathered from the ongoing management of the pitches at this site will provide valuable information that will inform future pitch design and maintenance.