The definition of consistency here is the soils material consistency – its material state, not to be confused with consistency of a pitch in terms of ball bounce or pace.
There are three states of soil consistency: Solid (the soil breaks by fracture), Plastic (the soil fails by flowing or moulding like plasticine) and Liquid (the soil has no yield stress and will flow – such as in mudflows). As water is added to a dry, compacted clay soil, as typically used in cricket pitch, the soil will move from a solid state to a plastic consistency. Addition of more water would move it from a plastic to a liquid consistency. The liquid consistency state should be avoided at all times but the transformation between the solid and plastic consistency is commonly used in rolling and pitch preparation – the pitch is wetted to make it plastic so that when it is rolled it is easily deformed and smoothed, it is then allowed to dry and move to a solid consistency where it becomes hard and ball bounce and player traction (grip) is improved.
Figure 1 This diagram shows how the consistency of a soil will change from solid to plastic to liquid as the water content is increased. At the plastic limit, the soil will change from failing elastically to failing plastically – what this means is that it stops crumbling and shattering and starts to mould and flow. At the liquid limit the soil has no yield stress – that means it will flow under its own weight, like liquid water. The actual values for the plastic limit and liquid limit presented here are for Ongar Loam, other loams will have similar but slightly different limit values. The ideal zone represents the range of water contents at which the soil is in an ideal consistency for solid tine aeration in cricket pitches, i.e. it is not too solid and not too plastic. This range of water contents is very small in cricket loams.
Tine penetration is easier when the soil is plastic but the soil flows around the tine. When the soil is friable (i.e. not so hard it is impenetrable, but it still crumbles rather than flows) the tine will help to break the soil around it, creating fissures and new pores which extend beyond the region of the tine hole. Unfortunately in cricket soils the friable region has a very narrow range of water content so there is a rapid transition between very hard and plastic, so it can be difficult to get the soil at the right water content.
If the pitch profile is too dry, only shallow penetration can be achieved and this will damage the profile as it will fail upwards – i.e. it will lift as the tine is pulled out, damaging the profile and pitch surface.
If the pitch is too wet the tine will simply push the soil into the walls of the hole and the effect will be limited. Harm can also be done when the soil is too so wet that the aeration equipment damages the soil as it travels over the pitch.
The ideal consistency to be at on cricket pitches is just on the wet side of friable. This might reduce the effectiveness of the operation but it significantly reduces the risk of harm to the pitch from shallow penetration and vertical uplift. For solid tine aeration of outfields – a little drier is ok because the effect on the outfield is less.
One tip for getting the right soil conditions is to keep trying as the pitch gets wetter to get good penetration. Of course this is easier when you own the equipment and more of a challenge when the equipment has to be borrowed or hired.