STAGE 4: SELECTING THE RIGHT TECHNIQUE AND MACHINERY

Having identified the problem, you can now identify the solution. The key here is to understand that there is no such thing as the ‘Wonder Aeration Tool’ that addresses all problems at once. We need to match the right tool to the problem identified and if there is more than one problem, more than one tool might be required. This stage identifies which machines do what and how to select the right machine to use.

There are two main machinery types:

· Machines for treating thatch problems

· Machines for treating rooting / layering problems

Deep scarification machines help to reduce thatch but little to encourage deep root growth or gas exchange at 150 mm deep in the profile (and vice-versa with the solid tine aerator).

Machinery Selection Summary

This table will help you match aeration equipment to the problems identified in Stage 3. The machines are detailed in the following section.

machines are detailed in the following section.

	Square									Outfield
	Thatch					Shallow rooting	Root break
Depth	Limit-ation	<10 mm	10-20 mm	20-50 mm	>50 mm	<20 mm	20-60 mm	>60 mm
Scarifier	y	y	-	-	-	-	-	-	-	m1
Deep scarifier	y	y	y	m	-	-	-	-	-	y
Fraise mower	x	m 2	y	-	-	-	-	-	-	-
Surface planer	x	-	-	y	-	y	y	y	-	-
Solid tine aerator	-	-	-	-	-	y	y	y	m 3	y
Hollow tine aerator	x	x	x	x	x	x	x	x	x	m 4
Deep Drill	-	-	-	-	-	y	y	y	m 5	m 6
Drill and Fill	-	-	-	-	-	-	-	y	m 5	x
Surface reconstruction	N/A	x	m 7	m 7	y	y	x	m 7	y	N/A

Key: y Suitable, m possibly suitable, x unsuitable – do not use, - no or little effect, N/A not applicable.

Notes:

1. Tractor mounted equipment only due to work rates.

2. Fraise mowing can be used to reduce near-surface thatch but the costs of topdressing and overseeding could be relatively high, this approach is more suited to higher level cricket venues.

3. The effect of the solid tine aerator on deep root breaks will depend on the working depth relative to the depth of the root break.

4. The hollow tine aerator can help limit thatch development in high sand content drained outfields found in international venues but for the majority of grounds, outfield aeration is best achieved with a solid tine aerator.

5. The effect of the deep drill / drill and fill will depend on the depth of the root break, however deep (>60 m) root breaks will have less of an effect on pitch performance than shallow root breaks.

6. The deep drill work rate is relatively low and will limit the cost effectiveness of this strategy at a whole-outfield scale but use of the deep drill in targeted areas could be beneficial.

7. Quality surface reconstruction can control thatch and root breaks but is relatively costly compared to other methods. There is an effectiveness-cost trade-off.

Machinery types

Scarifiers and Deep Scarifiers

Scarifiers can be as simple as a rake used to lift surface thatch, trampled grass, horizontal grass and stolons. Motorised pedestrian scarifiers use wire tines or blades to provide more aggressive grass and thatch removal but are limited to the top 5 mm of the profile. Routine use of scarifiers in pitch preparation and following the use of a pitch in-season will help to reduce thatch accumulation and maintain pitch performance.

Deeper scarifiers, sometimes called ‘Linear Aerators’ have steel blades driven by a larger engine designed to work at a greater depth in the profile (up to 15-18 mm depending on soil conditions – note working depth is rarely the maximum working depth quoted by the manufacturer when working on dry compacted cricket soils). These are more effective at removing thatch than standard scarifiers and will remove large quantities of thatch from the surface to the working depth. These machines are best suited to end of season renovation work.

Note that scarifiers will slow the rate of thatch accumulation but are unlikely to reduce it to zero. Also they are limited to their actual working depth – they will not remove thatch that is deeper than the working depth. The depth of thatch can be measured from the core sample (see Stage 3). The working depth can be measured by inserting a thin blade or screwdriver into the channels cut by the scarifier. Always measure working depth in this way – do not rely on depth gauges on the machine. A scarifier cannot remove all thatch within the working depth in a single pass and a number of passes in different directions (usually up to three) might be required, but this still not remove all the thatch and so routine pre-season / end of season thatch removal is advised if you have a persistent thatch problem. Excessive use of the deep scarifier on a single occasion can cause the surface to become unstable.

The Fraise Mower / Surface Planer

Fraise mowers and surface planers are commonly the same machine. They are a tractor mounted, PTO driven machine that has a series of small horizontal blades on a scroll, which cut or plane the surface and then feed the planed soil onto a belt elevator that then throws the soil into a trailer towed alongside. The difference between fraise mowing and surface planning is the working depth. Fraise mowing aims to remove the grass to its crown or just below, removing surface thatch as it does so. This is an effective method for reducing the shallow rooting weed grass species Poa annua (Annual Meadow Grass) and for improving the number of desirable grass plants in the sward by re-seeding.

Setting the working depth deeper into the profile will result in surface planing as soil is removed. The surface can be removed in layers, to the target depth (defined by the thatch depth measured in Stage 3. Typically surface planing is used to remove a maximum of 50 mm from the profile. It is unlikely that a cricket pitch will have a 50 mm thatch layer but it could be affected by thatch layers buried to this depth. If you are removing large quantities of soil using this method, then it will be necessary to restore surface levels by reconstruction using imported loam of the same type used in the square construction. Suitable square levels must be maintained and the square should always be proud of the outfield and not dished like a bowl – this is to prevent ponding and water running onto the square.

By changing the blades, the surface planer can be transformed into an effective deep scarifier which is increasingly used in end of season renovations due to its larger working width.

Surface planers are often owned and operated by contractors. This is because the equipment is expensive to purchase and operate, would be used infrequently at any one cricket club and requires experienced operators. If you identify thatch layers greater than 15 mm or root breaks that are within 50 mm of the surface then speak to your County Pitch Advisor for the recommendation of a specialist cricket contractor who has experience of operating these machines on cricket squares.

Solid Tine Aerator

The solid tine aerator is now the most common aeration tool found in sports surface maintenance. It comprises a series of solid tines that are driven into the ground using a cam-action. The tines are mounted on a cam that is powered either by a petrol engine on a pedestrian machine or by the PTO on a tractor mounted machine. Generally, pedestrian machines allow greater flexibility of use as they are lighter but tractor mounted machines are wider, more powerful and heavier and as a result achieve greater working depths and work rates.

Working depth is set partly by the machine (commonly using a depth control roller) and partly by tine diameter. This is important when using solid tine aerators on cricket squares because working depth is affected by tine resistance. The amount of resistance will decrease as the tine diameter decreases, i.e. in the same soil condition a narrower tine will penetrate deeper than a wider tine. Narrower tines have less strength however and will be more likely to snap, and they also affect a smaller volume of soil. So there is a trade-off between strength and penetration depth but narrower tines are still effective as they are still much greater in diameter than the plant roots. Matching tines to soil condition is important and will be discussed more in Stage 5.

Most solid tine aerators will be able to adjust the angle at which they exit the soil – the further from vertical this is, the more the surface will be heaved. Heave on a tine will result in decompaction (it lifts the soil upwards, increasing volume and therefore decreasing density) – however it will also disrupts surface levels. For this reason it is important that solid tine aerators are not used with heave when used on squares – otherwise significant damage can be created, with high repair costs and closure of a square for months and even a whole season. On a cricket square the machine should be set so that the tine enters and exits vertically. For this reason it is also important to match forward speed to tine penetration speed. On an outfield, a small amount of heave in the right soul conditions will help relieve outfield compaction without significant surface disruption but heave should not be excessive or it will affect ball roll or require rolling of the outfield that will undo any benefit achieved by aeration.

The classic view of solid tine aeration is that insertion of the tine into the soil creates a series of cracks in the soil, radiating from the tine hole that help introduce air to the soil at depth and conduct water from the surface (Figure 1b). For this to happen the soil must be in a relatively dry and brittle state (it will crumble and fracture as it is disturbed). However this soil state is often too hard to allow tine penetration in solid tine aeration, and even with the deep drill. This brittle soil condition is likely to exist at the end of the season but aeration of this type is commonly delayed until late October – November when the soil is wetter and tine penetration is easier and results in less surface deformation.

Figure 1 Solid tine effects on cricket pitches. It is essential to ensure that the tine enters and exits the soil on the same axis and that this axis is vertical. If the tine is rotated in the soil as shown in (a) then surface disruption will occur – machines should be set up to ensure that heave is avoided and that tines enter and exit the soil vertically. (b) shows an ideal creation of fractures as a result of using a vertical solid tine. Commonly, this does not take place because in order to create these fissures the soil needs to be dry enough to achieve brittle failure but in this condition it is too hard to achieve tine penetration to full working depth. The situation in (c) is more common where the soil is wetter to achieve penetration but then fails plastically – with localised compaction around the tine hole. This compaction must breakdown through shrink and swell action before the tine hole is fully functional.

But in October - November the soil is more plastic and it will mould like plasticine around the tine. In this state, soil is moved sideways creating compaction around the hole walls (Figure 1c). Over time this compaction is restructured by shrink and swell, allowing water and gas to move through the tine hole walls. Also, grass roots will grow down these holes and allow greater depth of root penetration in the hole.

Figure 2 Illustration of the effect of deep drill /vertical solid tine on grass rooting in a soil that is dense at depth. Roots exploit the channels created by the drill /tines, surrounding plants unable to access these channels remain rooted in the less dense upper layers.

The Deep Drill

The Deep Drill is a self-propelled machine that has an array of drill heads into which auger drill bits of different diameter can be fitted. The drill bits are then lowered into the ground and then lifted out before moving forward to reinsert the drill bits. The advantage of this method over solid tine aeration is that the drill bits cut the soil, resulting in less sidewall smearing and larger tines can be used because of the drill rather punch action. This allows larger tines to be used in drier conditions but soils still have to be moist enough to allow the drill bits to enter the soil without snapping. A snapped drill bit is difficult to recover without causing localised damage.

The equipment can be used in two ways:

· ‘Deep Drill’: narrower (10-12 mm) drill bits at close spacing, holes not filled but allowed to close over time. Excavated soil is brushed and removed. This allows gas exchange at depth and roots to grow down hole. It results in very localised decompaction in the tine hole but has a limited effect between holes. Tine diameter should not be too large otherwise localised cracking and subsidence into the hole will cause problems with surface levels and ball bounce.

· ‘Drill and Fill’: larger diameter (18 mm) drill bits at wider spacing. Excavated soil is brushed away and then the holes are manually packed using the same cricket loam used to construct the pitch. Soil is poured/brushed into the hole and then compacted by hand using a solid rod of metal or wood. Each hole has to be filled so the process is labour intensive and extremely time consuming but the aim is to provide a tie between surface layers and layers at depth where a root break has occurred.

On average it takes 4-5 days to complete the drill and fill of four pitches on a double pass of the machine using 25mm drill bits (in good weather).Drilling takes place on Day 1, along with clearance of the spoil at each pass. The remaining three to four days are spent filling the holes by hand (usually a team of three) and final clean up at the finish.

This process is sometimes called ‘nailing a pitch’. This method was not trialled in the research, reports on effectiveness when used by cricket clubs varies but it has been found to be effective in some cases. It is a lower cost technique compared to surface reconstruction, where free volunteer labour is available – where labour is paid for, then the cost of labour must also be considered.

Figure 3 The process of reinforcing a cricket pitch using the ‘Drill and Fill’ technique (sometimes called ‘nailing’ a pitch). Larger diameter holes are drilled through the root break and loam is manually compacted into each hole using a piece of doweling or similar. This is a time consuming process but is lower cost than surface reconstruction.

Hollow Tine Aerator

The hollow tine aerator is similar to the solid tine aerator but the tines are hollow so that they remove a plug of soil as they exit the soil. They are commonly used on golf greens to reduce thatch by pulling small cores of sand and thatch out – the cores are then collected and composted. The greens are topdressed and sand brushed into the tine holes. This effectively replaces the thatch with new rootzone. This procedure does not work on cricket pitches because the soils are much harder and it is difficult to brush clay loam back into the holes and achieve sufficient compaction – this results in a dimpled surface. For this reason the use of hollow tines is extremely rare on cricket pitches.

Hollow tine aeration does have a role to play in reducing thatch and improving infiltration on some cricket outfields where they have full drainage schemes in place and are routinely topdressed with sand (this is limited to a small number of international cricket grounds in England and Wales). For the majority of cricket club outfields – a simple solid tine aerator would be effective.

Sarel Rollers and Slit Tine Aerators

A number of clubs will have access to hand tools such as Sarel Rollers (rollers with solid wire spikes) and rollers with slit tines. Such rollers are also available as self-propelled or tractor mounted devices. These devices do not loosen or decompact the soil but can help in the process of seed establishment – see Routine Aeration for Cricket Pitches[IJ1] . Do not use these rollers when the soil is too wet because they were shown to smear the soil with little benefit in the trials at Cranfield University.

Slit tine aerators should be restricted to the outfield and not used on squares as they can cause adverse cracking patterns.

Slit tine equipment should not be used on a cricket square (left) as it can cause cracks to form (right) by creating planes of weakness in the soil.

Back: Stage 3 – Problem Identification

Next: Stage 5 – The Aeration Treatment - Method and Timing

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