Sports Turf

Science, construction and maintenance

V.I. Stewart

• Publisher: Routledge
• Year: 2004
• ISBN:
  9781135833718
• Edition: 1
• Topic: Arquitectura
• Subtopic: Arquitectura general

A detailed, practical guide (with the backing of the main UK authorities) to the construction and maintenance of sports grounds.

Part One

General Principles

Chapter one

Identifying the problems

1.1
The needs of sport

Turf surfaces used for sport must be moist enough to sustain the grass, but not so moist as to affect adversely the quality of play. They will vary in character according to the special requirements of different games and the standard of provision that can be afforded. For instance, the artificial drainage system which a first-division soccer club might feel was essential to ensure play in all but the worst weather conditions could not normally be afforded or justified by the average sports club, or by a local authority responsible for the provision and maintenance of playing fields out of public funds.

Those involved in new constructions are very frequently asked to specify the usage that can be expected from the final turf surface. Such a request seems reasonable, especially from a club or educational establishment for which use has to be matched to a fixture list or integrated into a fixed timetable. In this respect, however, grass pitches can be a problem. Although grass is ideal as a playing surface when fit for play, it is not so reliably programmable as the more expensive synthetic surfaces.

An improvement in the quality of a surface, suiting it better to the skills of the game, can often be quite easy to assess. For example, the pace of a cricket pitch can be determined by the rebound of a cricket ball dropped dead onto the playing surface from a height of 4.88 m (16 ft). A bounce height of less than 508 mm (20 in) is slow, 508–635 mm (20–25 in) easy paced, 635–726 mm (25–30 in) fast, and so on. The time a perfectly weighted bowl will take to roll to a stop over a standard distance of 30 yards (27.42 m) can be used to assess objectively the pace of a bowling green. A slow green will require a weighty, robust delivery to achieve the distance but will rapidly decelerate as it reaches the mark, rolling to a halt in only 8–10 seconds after release. This compares with 14–18 seconds for a fast green where the bowl can be delivered with much less weight, or the 21 seconds that can be achieved on New Zealand's Cotula greens.

Improved performance in terms of the number of games a surface will take in a given period, though often asked for, is difficult to specify. Intensive use probably begins at two adult games a week and accumulative damage can become critical at three games a week, even if play is avoided when the surface is squelchy. One game played on a squelchy surface, at any time in the winter, may so damage the sward as to affect performance for the rest of the season.

If play is confined to the summer period or to children of 12 or under, these criteria change dramatically. Five games per week, avoiding squelchy conditions, might represent intensive use by children, but here the quality of play can be a problem, concentrating damage down the centre of the pitch and especially in the goal areas.

These conclusions on wear are supported by evidence of the following type.

1. A senior club playing first and second team games on their main home pitch may well average two games per week each season. By the end of the season most of these pitches are badly in need of far more renovation work than the average school or parks pitch would expect to get.

2. An extensive vegetation and soil survey of league soccer pitches at the end of one season revealed how frequently pitch deterioration was blamed by the groundsman on the one game that was played when it should not have been (Thornton, 1978). The trouble is that once the sward has been broken there is virtually no chance of recovery during the winter. Instead, bared areas tend to extend because of the low shear strength of the non-root-bound surface.

3. Tear wear begins when a stud or heel breaks into the surface. This is most likely to happen when the surface is wet. A well-drained soil, though moist, will often feel firm underfoot. Under these conditions the weight of a child is scarcely sufficient to cause studs to penetrate but, with adults, stud penetration may be readily achieved. This explains the big difference in the effect of child and adult use, a point not always taken into account by those who advocate the dual use of school playing fields by children and adults.

4. A qualitative scale used in agriculture to monitor surface wetness after drainage makes use of the following hierarchy of categories:

(a) hard and cracked;

(b) firm and dry but not cracked;

(c) firm and moist;

(d) moist and soft;

(e) squelchy in patches;

(f) squelchy all over;

(g) pools of standing water;

(h) surface awash.

If we could persuade referees, who are the only people officially sanctioned to cancel a game, to cancel all games when at least one third of the surface is squelchy, and to allow games only exceptionally, i.e. no more than one game in a week, when the surface remains moist and soft, the staying power of our swards would be greatly enhanced.

5. Even with the same soil and the same general intensity of use, effects determined by climate, shading and standard of maintenance may also modify performance, as in the following examples.

(a) Features of climate such as rainfall and temperature vary significantly across Britain. Thus, in Wales, there is a risk of ‘puddling’ or ‘poaching’ because of excess soil moisture from September onwards, whereas in East Anglia, the same conditions are not to be expected until the beginning of December. In the north they have more frequently to face the dual hazards of rain and frost.

(b) Shading by grandstands can weaken growth through reduction in light intensity, reduced evaporation and increased persistence of frost.

(c) Height of cut, frequency of cutting, regular over-seeding with the stronger-growing grasses, proper fertilizing, pest control, special treatment and care of goal areas, the immediate treading back of turf torn out during play: all these features, in addition to good drainage, distinguish good maintenance from bad and affect the survival of a sward through the winter.

(d) Park pitches or school pitches cannot always be patrolled out of hours to stop boys ruining the goal areas by ‘kicking in’. Children would rather have the alternatives of mini-goals and a mini-pitch of their own but too few of these are provided.

With so many factors contributing to the fate of a sward in use through the winter it would be foolhardy at present to predict the consequences of any particular pattern of usage defined solely in terms of hours of play. What can be said is that sound construction, good maintenance, a dry climate and discretion in use will all contribute favourably.

1.2
Effects of poor drainage

Poor drainage quickly becomes apparent as soon as too much play is permitted in wet weather. It may then be too late to remedy the situation until the winter is over and meantime, poor playing conditions, cancellations and disruption of fixture lists will probably be difficult to avoid. It is, however, the long-term effects which are likely to be most damaging. Excess surface moisture over a long period will generally lead to:

• greatly reduced aeration of the soil;
• reduced root development;
• less resistance to tear wear;
• less resistance to drought;
• inefficient use of plant nutrients;
• late and slow growth in the spring;
• increased susceptibility to disease.

The end result is a grass cover insufficiently durable to support the amount of use normally expected from a winter games pitch.

Most of our sports-field drainage problems are not to be attributed to the ill effects of too high a ground watertable. More typically, water from a shower of rain fails to penetrate below the immediate surface even though the soil beneath is quite dry. The problem, in fact, is one of free water perched over trapped air.

Though air appears to be empty space available for filling by water, air must be able to escape before water can move in to take over the space that the air occupied. The problem becomes clear when water is poured too rapidly into a narrow-necked bottle. The water cannot get in if it blocks the only passage through which the air can get out. This is very similar to the situation in soil when a period of intense rain floods the surface and the infiltration of water is then impeded by water obstructing the upward escape routes for air. Thus drainage can become as much a matter of the movement of air as the movement of water.

The problem of the competition for pore space between water and air becomes worse the more uniform the pore size. Given a range of pore sizes the capillary forces will ensure that eventually the water is preferentially drawn into the smallest pores. This leaves the air to coalesce into progressively larger bubbles in the larger pore spaces, making escape even more difficult unless the large pores form part of a continuous channel linked through to the surface. Here is one benefit that earthworms, old root runs, cracks and soil granulation can confer to the mature soil, but this structure may be lost during disturbance and stockpiling. It explains why the click of air bubbles bursting can often be heard if one jumps to shudder the soil round a temporary pool of surface ponded water.

Only where the soil is well endowed with large pores and is closely underlaid by a drained gravel bed is air likely to be pushed down through the soil and cleared along with the drainage water. In all other circumstances it has probably to be cleared back up to the surface, a possibility more likely to occur in response to light rain that fails to flood the whole surface. The gentle fine rain that the farmer prefers can be safely absorbed by a well-structured soil into the small pores within soil aggregates, leaving the large pores between aggregates free for the simultaneous escape of the displaced air. However, on the ‘poached’, de-structured surface of an abused sports field the whole soil is small-pore in character and a false surface water table can be rapidly established over a drier layer of air-locked pores.

This is the classic situation that requires drainage water to be by-passed through specially installed, freely permeable, vertical slits, linking the surface directly though to the underdrains.

1.3
Climate

Climatic effects of importance to sports turf are not to be summarized simply by reference to temperature and rainfall considered separately. Frequently, it is an evaporative effect caused by the interaction of rainfall and temperature that more clearly d...

Table of contents

• Cover
• Half Title
• Full Title
• Copyright
• Contents
• Preface
• Acknowledgements
• Introduction
• About the NPFA
• Part One General Principles
• Part Two Specific Constructions
• Part Three Appendices
• References
• Index