WHAT CAUSES ROOT BREAKS?

Root breaks are a complex feature of cricket pitch.  Root breaks can occur at any depth within the profile but the nearer the surface they are, the more likely they are to affect ball bounce.  As the layer forms, grass root growth exploits the large void created and tends to grow horizontally (Figure 7).  This creates a shock absorbing layer that reduces the ball energy on impact and slows the pace and bounce of the pitch.  It also will vary across the pitch, making it more variable.

Figure 7 The effect of root breaks in cricket pitch profiles on grass growth.  The root break provides a low resistance path for grass roots to grow when compared to the compacted soil below.

 

Root breaks are caused by a combination of factors including:

1.       The construction of pitches in layers

Typically pitches are constructed in compacted layers of 50 mm.  If the next layer is not keyed into the previous layer by raking or scarifying the surface of the lower layer then breaks at 50 mm will be manufactured into the profile.  Even when constructed in 50 mm layers the top of the 50 mm layer will be more compacted than the soil below so careful construction is essential.

 

2.       Topdressing with incompatible soil loams

It is essential that any topdressing or reconstruction work uses the same loam as soils lower in the profile, otherwise they could shrink and swell at different rates which could lead to a fissure developing between soil layers.

 

3.       Natural shrink-swell behaviour

The clay loam soils used for cricket pitches shrink and swell and they do this more nearer the surface because there is less overburden from other soil above confining the shrink and swell.  Without careful rolling to maintain near surface compaction, significant differences in density can occur.

 

4.       Rolling when the soil is too wet

The Cranfield University research on rolling showed that roller can move the soil backwards and forwards as well as downwards during rolling.  This horizontal stress on the soil can cause soil in the top 50 mm to move relative to the soil below when the soil is too wet.  This is particularly a problem with heavy, small-diameter rollers (diameters < 500 mm).  Rolling in the right conditions is essential to prevent this damage.

 

5.       Root growth impedance in high density soils

The effect of compaction on root growth is shown in Figure 5 and Figure 6 which show how high density soil causes shallow rooting and a near-surface reduction in density.  The grass itself creates a layer as it loosens the soil.

 

6.       Shallow aeration practices

Cultivating the soil near the surface to make shallow slits and spike holes can create a loose layer over a more compacted deeper layer.  This is then exploited by the grass roots, creating a break.

 

In reality it is likely to be a combination of these factors that lead to the formation of a break but pitch construction and the use of the correct soils is essential in limiting their development.  Strategies for addressing root breaks vary with the depth of the root break, the extent of the root break across the pitch/square and the available budget.

 

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