Chapter six
For detailed instructions on specific maintenance programmes refer to sections 10.5 and 11.13, and Appendix 6.
Interrelationships of sward biology, construction, maintenance and use
6.1
Establishment and immediate after-care prior to allowing play
While the soil is still relatively loose the juvenile roots of the grass may be encouragingly long, but the sward will not be firmly established until the root system develops into a fibrous, much-branched, intertwined tangle.
The introduction of sand or sand/gravel slits, to complete the job of surface water interception, may well be delayed until a sward has been established. This will make it easier to excavate narrow, stable-sided trenches. Thus establishment of a sward may have to proceed in two stages: first by an initial seeding prior to slitting, and then by over-seeding to repair damage following slitting. This can provide the opportunity to establish, at the initial phase, a sward of the slower-germinating, lower-growing, bottom grasses, such as the browntops and smooth-stalked meadow grasses. The more easily established, more vigorous growing rye grasses can be introduced later, e.g. by slit seeding.
Immediate after-care usually involves cleaning up, re-truing and firming down the soil surface, over-seeding to repair damage and fill gaps in the original sward; also fertilizing, irrigating and sand topdressing, nursing the sward through to a firmly anchored, dense, uniform covering of vigorously growing grass.
6.1.1
The soil surface
It is assumed that the bulk of the work required to achieve a true surface will have been carried out before grassing up. However, if more drainage operations are carried out through the initial grassed surface, this may require further time to be spent on more stone picking, surface truing and light rolling. After this final construction stage further surface truing will have to be by repeated cycles of sand topdressing, co-ordinated with over-seeding.
6.1.2
The sward
Sward maintenance in the early stages of establishment should aim at vigorous growth and deep rooting. This is largely a matter of adequate moisture, good aeration, proper fertilizing, and correct frequency and height of cut.
No play should be allowed until the whole surface is grass covered, including the sandy surfaces of pipe trenches and/or slits.
6.1.3
Fertilizing
Compensating for accelerated leaching losses
Constructions giving priority to drainage must inevitably risk continuous loss of readily soluble nutrients by leaching. This can be further aggravated by the fact that improved drainage is usually dependent on the liberal use of sand which is a poor medium for nutrient retention. The approach to nutrition should aim, therefore, either at slow release, or little-and-often application. Slow release is inevitable with phosphate fertilizers as phosphate is so insoluble. The problem materials are the nitrate, ammonium and potassium fertilizers which are generally highly soluble.
Sward establishment on the sand surface of slits or pipe trenches is bound to be difficult. Successful germination and establishment requires frequent re-wetting and this increases the risk of nitrogen and potassium loss by leaching. Therefore, special attention must be given to the regular replenishment of these nutrients until sideways rooting can be established into the adjacent soil. This is a factor to be considered when contemplating the installation of trenches more than 50 mm (2 in) in width. It also stresses the importance of the effort to try and include some nutrient and moisture-retaining organic component in the top 150 mm (6 in) of the sand backfill.
Any yellowing of the grass along the line of the slits and pipe trenches should be taken as a warning of a need for nitrogen, and possibly also potassium.
Stimulation of root branching
It has been known for years that root density is very much influenced by the distribution of organic matter. If the organic matter accumulates on the surface we have what might be described in soil terms as the ‘Mor’ condition, referred to in Table 8.1. Here, rooting is also concentrated at the surface, whereas with organic matter deeply incorporated, as in the ‘Mull’ condition, roots are distributed throughout the soil. The reason for this relationship has been explained by experimental evidence (Drew, 1975) showing that root branching is a response to the presence in solution of available forms of nitrogen and phosphorus. This does not affect the behaviour of the primary, exploring roots; they seem to be adapted to explore the soil in depth, controlled only by their need for adequate aeration. Thus a medium providing for satisfactory rooting must allow for the exploitation of a large volume of soil by branch root proliferation in response to incorporated sources of available nitrogen and phosphorus. If the primary root can carry this process deep into the soil then the plant will not only be well equipped to secure its nutrient requirement, but also well anchored and buffered against drought.
All sources of phosphate applied to a soil are rapidly immobilized by association with calcium, iron or aluminium, whereas ammonium and nitrate sources of nitrogen remain freely soluble. It must frequently be the location of the applied phosphatic fertilizer, therefore, that will effectively control the distribution of the mass of plant feeding roots. With this in mind we should take advantage of the opportunity during construction to build sources of phosphate into the soil within rooting depth and, during subsequent maintenance, take steps to only apply phosphate when it can be fed down into spike holes or incorporated by a subsequent topdressing of sand or loam.
6.1.4
Fine sand topdressing
Topdressing with fine sand (e.g. a topsoil sand such as SN 12–15 in Table 7.1) is an important feature of the maintenance of any sward used for sport but, with new constructions involving surface slitting, it is particularly important to topdress generously before the first season of winter play. This general topdressing is necessary to help true the whole surface and protect the slits from being capped by soil. The minimum cover that should be achieved before allowing play is of the order of 80 tonne/ hectare (30 tons/acre), i.e. a covering of 5 mm in) overall. To avoid any risk of smothering the sward this should be applied in two increments, allowing adequate time for sward recovery after each application has been thoroughly worked into the base of the sward. Purpose-made machinery is now available to ensure an even spread at a rate that will achieve the necessary application in each pass. Provided the sand can be kept dry, an alternative, DIY procedure involving a tractor-drawn, rigid, metal lute, some 2 m wide, can be used to spread the sand from pre-placed heaps or regularly spaced bands, levelling the surface simultaneously. If the grass is not to be smothered, both the sand and the surface must be dry enough for the sand to fall freely into the base of the sward, exposing the leaf tips to sunlight.
In order that all the foregoing operations can be performed in the right conditions, eg. fertilizing and seeding when conditions are likely to remain moist and topdressing with fine sand when the surface is dry, it is essential to make adequate preparations in advance.
6.2
Considerations for the long-term maintenance of new constructions
6.2.1
Surface sanding
A sand-slit top cannot hope to retain its trueness and drainage efficiency permanently without continuous, careful maintenance. The differential response of sand and soil to the swelling and shrinking effects of wetting and drying leads to the slit surface sinking relative to the surrounding soil (Figure 6.1). The resulting washboard effect can be off-putting and dangerous for the players. If allowed to persist, or if corrected by heavy rolling in wet conditions, the end result will be drainage deterioration because of soil capping the slits.
This trend must be anticipated and counteracted by an annual topdressing of fine sand (topsoil sand) applied during a dry spell in the late summer before the playing season starts. The method of application must ensure that the sand can be drag-brushed or luted into depressions, particularly the depressions along the line of the slits. After a 5 mm (1/5sin) application of sand before the first season of play, the minimum annual rate of application thereafter should be of the order of 40 t/ha, or 2.5 mm overall (16 tons/acre or 1/10in).
More than one such topdressing annually could well be beneficial but cost, and the practical possibilities of achieving this, make it very unlikely. The other alternative of increasing the amount of sand applied in a single topdressing carries with it the risk of sward damage by smothering. However, a single application of 25 mm (1 in) was successfully applied in a single application onto a vigorous ryegrass sward at Cardiff Arms Park in the summer of 1972.
6.2.2
Surface response
Choice of sand for construction or topdressing affects not only drainage but some of the
FIGURE 6.1 Essential maintenance to overcome the problem of progressive settlement within slits, (a), (b), (c), and (d) illustrate how slits may be affected by seasonal variations in soil moisture conditions because the soil and sand/gravel fill will respond differently. Whereas the sand and gravel will neither shrink nor swell significantly they will readily settle down into any extra volume made available within the slit. The soil, however will shrink in depth and contract horizontally in response to desiccation (a-c), then swell back to its former volume, though not necessarily its former shape, in response to thorough re-wetting (d). (e) Topdressing and re-truing the surface with sand, when the soil is fully desiccated, cases (b) and (c), will avoid any adverse effect on the efficiency of the slit system by ensuring that surface water continues to have free access into the slits.
playing characteristics of thesurface and itstractive efficiency.
For the bounce-deadening response of golf greens we need uniform, rounded particles that will ‘hold’ by yielding rather than becoming dense, rigid and potentially ‘fiery’.
On a bowling green there is no need to make provision for bounce. Priority instead can be given to trueness and the pace of the roll of the bowl. For these qualities to be achieved with a quick-draining sand soil, roundness and uniformity of particle size have not the same priority.
For vigorous winter games tractive efficiency depends on the dryness of the surface and the grip achieved by a studded boot. Players require the surface to give sufficiently to allow the studs to penetrate, but not to shear. To ‘give a stud’ without having to be wet, the sand forming the surface should have the same uniform roundness that is required on a golf green, but no sand of this type will provide any significant tractive strength when dry. This means that, for the most part, the tractive efficiency of such a surface, when dry, depends primarily on the root-binding strength of the sward.
However, such surfaces are seldom dust dry in winter and any moisture present can contribute significantly to tractive efficiency, even without the assistance of grass. With the addition of water, tractive strength increases as particle size decreases, reaching a satisfactory level for play when water-bound, like fine sand in the inter-tidal zone of a beach.
To have maximum effect for the improvement of soil permeability a sand topdressing should be carefully chosen. It should not only work on its own to readily transmit water, but when worked into the soil, should rapidly ameliorate the particle-size spectrum to peak at over 75% in the medium-to-fine sand categories. Using a sand of a wide, particle-size range tends to lead to a hard, dense, slow-draining soil because of the inter-packing possibilities presented.
In practice this means: (a) we should topdress with a very narrow particle-size-range sand, like dune sand which has 95% of its particles in the medium-fine sand range (topsoil sands like SN12, 14 and 15 in Table 7.1); (b) we should aim to match the dominant particle size in the top-dressing sand to the dominant particle size in the medium-to-fine sand categories in the soil (Appendix C).
The soil brought to the top by burrowing earthworms may not be identical in texture to the original topsoil. There seems to be a limit of about 0.5 mm to the diameter of particles ingested by worms so that, in time, their activities can effect a small shift in soil texture at the surface. One practical application of this knowledge is to use sand with a coarse sand matrix in slits and pipe trenches where worm activity might be expected to threaten the survival of the permeable link through the topsoil to the surface.
6.2.3
Deciding a policy about earthworms
The decision that should not be deferred
To base one's thoughts on construction and maintenance on the consequences that flow naturally from earthworms being present or absent may appear to be too abstruse and theoretical to have practical significance. However, in pasture, earthworms may number some 2 500 000 per hectare (1 000 000 per acre or 200 per square yard), weighing around 5 t/ha (2 tons/acre or 1 lb/sq yd) fresh weight. They turn over some 50 t/ha (20 tons/acre or 9 lb/sq yd) of fine soil annually, corresponding to some 25 mm (1 in) of fine soil placed onto the surface in the course of 10 years. They are well able to consume and bury all the grass clippings from a well-maintained sward in the course of a year. The influence of earthworms on soil is so fundamental that to fail to take their presence or absence into account would be like ignoring the influence of man when viewing the environment around us.
On sports turf a long-term decision has to be made on whether maintenance should encourage or discourage earthworms. It is particularly important that this subject is brought up for consideration early, ideally prior to construction. As farmers who have inherited land disturbed for opencast mining have good reason to lament, once lost, an earthworm population can take a generation or more to recover by natural colonization (Stewart et al, 1988).
To assist in the preservation of an existing earthworm population thought should be given to how any stockpiling of topsoil can be avoided. The aim should be to achieve transfer without any intervening period of temporary storage. Once in its new location, the topsoil should be worked through mechanically as little as possible because earthworms can be maimed and suffocated when their living space collapses around them. It is one thing to repopulate a soil from a viable residual population, but quite another to recover from complete annihilation.
Thus, unless prior thought has been given to this problem at the construction stage, a groundsman may find that the decision whether to work with or without earthworms has
TABLE 6.1 Plant adaptation to the soil development dichotomy, conditioned by the presence or absence of burrowing earthworms
High, pH typically above 6—Lime—Low, pH typically below 5
Succulent, palatable, plentiful—Organic matter—Fibrous, unpalatable, insufficient
Physically and chemical benign—Human intervention—Physically and chemically
hazardous
Adapted from Stewart and Scullion, 1989.
already been taken for him. If he does take over a soil with a viable earthworm population then he should review his proposed maintenance procedures for their likely impact on the population and the consequences for the playing surface should they be eliminated.
Encouraging the right worms
The importance of worm burrowing as an aid to infiltration, drainage, air circulation and rooting is now generally recognized but less so their beneficial effects in counteracting the build-up of thatch and in initiating the development of a granular soil structure (Stewart and Salih, 1981; Stewart, 1985).
As Table 6.1 suggests, there is much more that could be said about the possible evolutionary significance of the important dichotomous relationship between soils and vegetation developed in the presence or absence of burrowing earthworms. The general consequences for sports turf are summarized in Table 6.2.
However, not all earthworms are equally effective for soil conditioning. Of the 25–30 species of earthworm found in Britain only five are of any great importance for their beneficial effects on the incorporation of organic residues and the natural drainage of soils under grass. These are generally the worms that grow to a size longer than 75–100 mm (3–4 in) when mature. Unfortunately, the relatively large worm species most commonly available to fishermen, the Brandling (Elsenia foetida) is not an effective soil burrower. It breeds readily in wet compost and sewage, but will ingest very little mineral matter and does not survive long if introduced to a normal field soil.
TABLE 6.2 Construction options and maintenance requirements conditioned by the presence or absence of burrowing earthworms.
All that can be done at present to preserve and prosper an indigenous population of burrowing earthworms under grass is to let the clippings lie, maintain the pH above 6 and avoid the adverse effects of pesticides. Many pesticides which are sold for the control of insects, nematodes, fungi and other organisms considered to be pests, also have lethal side-effects on earthworms.
Problems that the right worms bring with them
If earthworms are encouraged for the benefits they confer, it must be recognized that the surface they create will tend to be weedy and soft. They bring buried, viable, weed seeds to the surface in their casts and, at the same time, their casts provide open sites for aerially dispersed weed seeds to invade. Casts need to be dispersed by brushing when dry and the surface periodically rolled to reconsolidate. If the rolling closes the burrow openings the earthworms will soon open them again but the surface should never be rolled when the soil is wet enough to smear and pan. The fine soil brought to the surface in casts, yearly, can amount overall to a layer 2–3 mm in) thick, enough to cap an originally sandy surface unless diluted by the addition of further topdressings of sand.
Managing without the assistance of earthworms
On fine turf areas used for ball games such as lawn tennis, bowls, putting and croquet, where surface trueness is absolutely vital, worms cannot be tolerated and positive measures may have to be taken to discourage their presence. However, that should not be considered the end of the matter. In loamy soils the elimination of worms by wormicide or acidity leads to progressive soil compaction and associated problems with drainage. On the surface, organic residues accumulate leading to surface rooting, susceptibility to drought and an increased requirement for fertilizer which, if satisfied, can lead in turn to the lush growth that encourages insect and fungal pests.
All this has implications for construction and maintenance. The soil will either have to be constructed of sand or the surface sloped to disperse accumulating water. Maintenance will have to be of a very high order, incorporating tasks that earthworms would otherwise accomplish: removal of clippings and residual organic debris, top-dressing to bury exposed roots, extra fertilizing to compensate for the organic residues removed, greater vigilance over disease, pests and drought. It would be very negligent to wait until actual problems arise as all these consequences should be predictable to anyone aware of the dynamic nature of a grassland eco-system (Appendix 6).
Practical conclusions and the search for a compromise
The decision to encourage or not to encourage earthworms varies for different games and, therefore, may vary within a single sports complex offering a range of specialist facilities. For example:
1.the beneficial effects of earthworms on drainage, soil structure and rooting are advantages that may tip the scales in their favour on areas in use throughout the winter;
2.assuming adequate provision for special maintenance, earthworms can be eliminated on small areas such as ornamental lawns, golf and crown bowling greens provided that slopes can be organized to achieve adequate surface runoff;
3.on large areas used for hockey or cricket, where a smooth surface is desirable, the situation is not so clear cut. Except for special venues these areas are too large to get the maintenance required, should earthworms be eliminated, and yet they could probably benefit from earthworm assistance with drainage.
What most groundsmen would like is a means of putting an earthworm population to sleep for the duration of a playing season, allowing them to return to full vigour for the rest of the year. This seems a tall order but recent research by Salih (1978) and Al-Bakri (1984) suggests an approach which might be developed in this direction. Their research has shown that the well-known tendency for the deep-burrowing species to retreat from the surface during drought may be part of a general reaction to anything which threatens their well-being. The sense organs of earthworms are chemo-receptors, very sensitive to changes in the chemistry of the soil solution. This probably explains why both Salih and Al-Bakri found that earthworms tend to avoid the surface of the soil when it has been treated recently with even relatively innocuous chemicals such as lime and ammonium-rich fertilizers, if these are applied in highly soluble and concentrated form. Eventually they will return but only after the concentrations have been significantly reduced by leaching. It could well be that the agro-chemical industry will take this up and develop purpose-made chemicals of this type to provide short-term relief from surface casting.
Fortunately, it is not easy to eliminate an established earthworm population completely by one treatment of a wormicide. Much will depend on whether the worms have a chance to take avoiding action. Though the adults are particularly vulnerable, recovery can be achieved within a year from any residual stock of viable cocoons. However, three treatments over a year to eighteen months should thwart natural recovery from juveniles and cocoons.
6.3
Construction options and maintenance implications
6.3.1
Options for the maintenance of a sufficiently sandy surface
Sand capping
Throughout this book a recurrent theme within maintenance is the need to apply regular topdressings of fine sand. This has been mentioned in respect of surface truing, maintenance of effective surface infiltration into slits, burial of organic debris and surface roots when earthworms are absent, and the dilution of soil brought to the surface in earthworm casts.
An alternative to an annually topdressed, slit scheme is an ameliorated fine sand carpet, 100–125 mm (4–5 in) deep, over slits placed between one and two metres apart. The large quantity of sand used in such a sand-carpeted scheme allows ample scope for heavy rain to be absorbed and temporarily stored within the sand carpet. This avoids any risk of even slight surface ponding, and the exposed sand surfaces of the underlying slits are very well protected against soil capping.
However, on a sand carpet skill has to be used in establishing a new sward from seed. The immediate surface dries quickly and young roots need nursing through to the underlying soil. As a seedling will have no difficulty pushing its way through loose sand to the surface, germination will be improved if the seed is well buried to a centimetre or more and firmed into place by rolling. It is only prolonged drought and the attendant risk of sand loss by windblow that is liable to cause anxiety, prompting some thought of provision for surface irrigation. For this reason there is much to be said for the sand-carpeting operation being delayed until the autumn when seeding can take place in a season not normally associated with drought.
As described in Chapter 6, the dynamic nature of a grass eco-system carries with it implications for maintenance that should be appreciated before decisions are taken on choice of construction. If earthworms are still present in the buried soil under a sand-carpeted surface they will bring fine soil through to the new surface. This need cause no anxiety in the first few years, but will require monitoring by soil testing to determine when annual, sand topdressing should begin. If a complete soil cap is allowed to develop it may be necessary to undertake some form of surface cultivation or hollow-tine spiking to achieve the required amelioration with sand. And even if worms are absent, there will still be a need to monitor the condition of the surface, in this case to look for signs of superficial accumulation of organic residues. If this occurs and is not treated by periodic scarification and annual sand topdressing it may lead to reduced wear tolerance because of excessive surface rooting, and damage from disease and pests.
In fact, after many years of appropriate maintenance, the sand slit and sand-carpet approaches should converge to a similar end product. A simple slit system normally starts with the original sward established in the existing topsoil, then, by substantial initial topdressing and annual repetition, a sand-ameliorated carpet is built up and the sward keeps pace by growing through. The sand carpet approach also begins with a scarcely less intensive slit-drained surface leading to piped underdrains. But what might be described as a vast amount of sand is required to form the sand carpet, and this means that an entirely new sward has to be established under what can be drought-threatening circumstances until the young grass has rooted through to the soil beneath. In due course the sand carpet becomes progressively modified by the incorporation of soil from below and organic residues from above so that again we can have a deep, sand-ameliorated surface overlying the original soil, and all the maintenance necessary to hold this physically viable.
Micro-slitting
This form of shallow, close-centred, sand slitting, aligned at right-angles to the main slits, can be used as an alternative to topdressing, but it is more expensive. If so used it can be carried out as the final constructional operation before play is permitted and then repeated at regular intervals thereafter. Alternatively, it may be used to re-establish efficient surface interception where the original slit system has become soil capped through maintenance neglect.
6.3.2
Improving permeability of the whole soil
As explained in section 1.4, any lasting improvement in the permeability of moisture-retentive soils used for winter games can only be achieved by altering their texture. Structural improvement achieved by mechanical means is seldom likely to be more than temporary.
Improving permeability at time of construction
Subsoil and topsoil cultivation
Severe compaction of the subsoil by heavy machinery during grading operations can be minimized by the avoidance of working when wet. Structural damage to fine-textured soils resulting from wet working can be difficult to remedy. If the ground is stony, subsoil cultivation to alleviate compaction should be carried out before topsoil replacement, then again to counteract effects of equipment used to return and spread the topsoil. The subsoiling involved should always be carried out under dry conditions to ensure maximum cracking and to avoid undue wheel damage.
Where a pipe drainage system is installed, further subsoil cultivation, or mole ploughing across drains, can be beneficial as a stop-gap until biological structuring processes have had time to develop, or some sort of stabilized slit system installed. However, subsoil cultivation would have to be repeated annually and this would only be possible if the damage to the sward was tolerable.
Topsoil inversion is no longer essential to clear the surface of weeds prior to seeding; chemicals can now do this job just as effectively. However, some light soil cultivation may be necessary to re-true the surface and prepare a seed bed, e.g. by shallow chisel ploughing, spring-tine harrowing or spike-tine, rotary cultivation. Here again the benefits to surface drainage will be temporary at best but can help through the phase of seed germination and sward establishment. There is a risk, however, that merely replacing the water-shedding efficiency of a compact surface by greatly improved surface infiltration may simply result in a soft, waterlogged topsoil unless there is also an adequate link to some form of effective underdrainage.
Addition of soil ameliorants
Whether earthworms are present or not there are good reasons in the dynamic nature of a grass eco-system why a sand top-dressing should feature in maintenance annually. It will either be necessary to dilute a capping of fine soil brought to the surface by earthworm casting, or to incorporate any residual surface accumulation of organic matter and roots. However, this also provides an opportunity for re-truing the surface, helping not only the run of a ball, but also the efficiency of water movement by surface flow to slits and, on fine turf in particular, the efficiency of close mowing. Nothing is worse than the alternation of lush growth in the low spots and moss struggling to green up the scalped surfaces of high spots, clear evidence of the need for surface regrading.
There is good reason to consider how any annual increment of sand should be applied, i.e. little and often or in one large application. Guidance on this is given in the general instructions on maintenance, sections 10.5 and 11.3. In any event, the minimum amount to be applied annually should be of the order of 40 tonne/hectare or 4 kg/m2 (16 tons/acre or 71/2 lb/ sq yd). The sand should be of a type with a narrow, particle-size range (0.125— 0.500 mm, e.g. a topsoil sand like SN 12, 14 and 15 in Table 7.1), biased towards the medium or fine sand end according to whichever of these particle sizes can be most easily reinforced to achieve dominance in the existing soil. To avoid loss of particles by solution it should not be lime rich, but where earthworm activity is to be encouraged, as on a general grass area used for winter games, a 5% lime content would help keep soil pH above 6. On acid, fine turf the sand should be lime-free or the sudden rise in pH may allow the opportunist fungal disease Ophiobolus graminis (now re-named Gaeumannamyees graminis) to invade, albeit temporarily. On the other hand, if a sward has long been established on a lime-rich soil, then further additions of a lime-containing sand will leave undisturbed the established biological equilibrium that in keeping Ophiobolus at bay.
If the necessity arises for the importation of topsoil, the opportunity should never be missed of selecting soil in which the medium plus fine sand content exceeds 75%. This provides a soil with good traction potential and a useful measure of rapid drainage, even when compacted by use (Appendix C).
Techniques of routine maintenance aimed at preserving or improving surface drainage after constructional work has been completed
If no thought has been given to the problem of maintaining topsoil impermeability at the time of construction, it may be extremely difficult to deal with this satisfactorily without incurring considerable extra expenditure on new drainage and the inconvenience of pitches being out of use while work is in progress. A variety of expedients are used by groundsmen in an effort to allow play to continue, but all too frequently this involves a great deal of work for a temporary benefit and in the long run, may only further aggravate a fundamentally unsound condition.
Spiking
Spiking is a procedure which groundsmen employ with varying degrees of enthusiasm. At first glance it would appear to be an obvious means of improving aeration and surface infiltration. Unfortunately this will only be successful where the soil condition being treated is a compact surface cap over an otherwise free-draining soil. However, spiking is often pursued as if it were a universal remedy for all conditions of surface waterlogging, whether or not there is a free-draining outlet at the end of the spike hole.
Forcing a metal spike down into the soil will not create any extra pore space unless there is a coincidental rise in the general level of the soil. There must be extra volume before there can be extra space. All that spiking will do, without any change in overall soil volume, is squeeze out a hole at the expense of pore space elsewhere, smearing the sides of the new hole in the process. The result can be a reservoir for infiltered water that may then be poached into the soil by treading.
If a real enthusiast for spiking is let loose on a field there is a risk that the whole process will have the same effect as the rodding of concrete. It is a useful experience to rod saturated sand in a bucket and feel how the sand compacts from the bottom up, requiring the limit of rodding to be progressively raised. No wonder that layers of compaction can often be found at depths corresponding to the limit of spiking.
If spike holes are to be inserted into a water-logging surface this should only be considered as an occasional remedial treatment in situations where contact can be made with free-draining material beneath. Otherwise, any insertion procedure should aim to create a continuous slit, linked across to the permeable fill of an artificial drainage outlet such as a sand slit.
Hollow-tine spiking followed by removal of cores is a useful remedial treatment for the control of thatch, the deep placement of fertilizer or the progressive lowering of troublesome high spots. But again, when the hole is used to insert a column of sand this will only benefit drainage if the sand links through to a freely permeable medium below. On desiccating high spots, in a sandy medium, the holes can be used to insert a plug of loam that may help in the retention of moisture.
Sand filling of cracks in clay soils
In clay soils the deep cracks that appear during periods of drought can be converted to a form of natural slit drainage by filling with a free flowing, medium or fine sand (e.g. SN12, 14 and 15 in Table 7.1).
This sand infiltration procedure will only be successful if carried out under very dry conditions with the surface smooth, the grass cut short, and the sand powder dry; easier still on a bare, panned surface as might occur in the early stages of construction. The procedure can be repeated annually as part of a general, fine sand, topdressing procedure, compensating for the progressive fall of the sand level as the surrounding clay soil swells and shrinks in response to changes in moisture content. So long as the cracks remain sand-filled to the surface they will improve the infiltration of water and, when linked to a system of mole drainage or stabilized slits, should also function for lateral discharge.
As this treatment is likely to be effective only for strong clay soils, here is one good reason for learning how to distinguish such soils by the method described in Appendix A.
Subsoiling
As described in Chapter 2, page 39, subsoiling can be an effective means of relieving compaction at topsoil and subsoil levels, even after the work of construction has been completed. However, it is a procedure which must be approached with caution. The nearer to the surface soil displacement takes place, the greater the risk of severe surface disruption. Under good conditions the heave can be organized to coalesce into an even elevation of the surface overall, but major horizontal cracking can provide space into which sand can leak away sideways from a slit system, hazarding the link with the surface. If the soil is bouldery or, worse still, incorporates debris such as glass or scrap metal, the playing surface may be rendered unsafe and any potential improvement in drainage may not compensate for the cost of reinstatement after hazard removal.
Rolling
Dry, loose surfaces or surfaces made soft by earthworm activity may become easily disrupted and scored by play, making reconsolidation and re-levelling necessary. If rolling is used it should never be attempted when the soil is in a soft, squelchy condition, and should not be used to carry out what should really be a grading operation. Injudicious rolling may achieve a temporary improvement in appearance, but if in the process the surface becomes panned or slits sealed over with soil, the longterm effect may be harmful.
Rolling is best carried out when the soil surface is moist but firm, a condition under which the soil will adjust to pressure by crumbling. Large stones and potentially hazardous objects exposed by surface disruption should be removed, not rolled back in. The circumstance in which rolling is most obviously beneficial is the consolidation of loose, sandy soil around seed. With loam and clay-textured soils, beware of panning the surface and excluding air from the sealed-in seed.
On balance, treat rolling with caution unless money is available to pay for the remedial treatment that may eventually become necessary. Re-truing by luting out topsoil sand will often be a better option.
Finally, because of the importance of appropriate maintenance, it cannot be reiterated too frequently that money spent on scientifically designed schemes of construction may be wasted if the subsequent standard of maintenance is not appropriate.