It would seem that while experts are more than capable of giving a particle analysis and generally understand why the Smectite or as it was once known, Montmorillonite soils swell and shrink in the manner in which they do, there is no real understanding regarding the cause of ‘Pace’ or why the ball bounces off the wicket in a forward direction at various speeds.

To begin to understand these ‘vagaries’ of the turf cricket wicket, an understanding of the basic principles of Soil Science is required.

A term used to describe the tests used to study the ‘bits and piece’ that go to make up soils.

To study the clay type soils required for high quality turf wickets used to play the game of cricket  the soils of Australia are used as the base example.

Generally, the wicket soil on the east coast of Australia have an analysis of the following: - Clay 55% - 60%, Coarse Sand 5% - 10%, Fine Sand 5% - 10%, Organic Matter 5% - 10%, Silt 5% - 10%. In Perth, the capital city of Western Australia, the clay content can be as high as 82% and so, together with the climatic conditions, the ball tends to bounce higher and faster, although extreme ‘cracking’ does occur which can make for difficult batting conditions at times.

It is the Sand/Clay ratio that provides the spin, turn or grip of a wicket, together with the amount of grass remaining on the surface, soil moisture and weather conditions. These conditions can vary from wicket to wicket and indeed it has been noted that wickets on the same wicket area or field can play differently should any the previously mentioned conditions vary at all.

To attempt an explanation of the way in which these particles interact to produce a wicket would take entire book of its’ own. This is an attempt to condense the soil science lesson to a few of the basic fundamental pieces of information.

In 1968 two researchers in the field of soils (Stewart and Adams) produced an interesting document. Part of this work reported that, as concrete needs cement so a binding soil needs clay. It was thought that a well-graded series of sand and silt-sized particles could achieve a considerable deduction in the amount of clay required to fill the remaining pore space, without a corresponding in binding strength.

These researchers went on to describe the soils used in England which in their opinion produced the ideal wicket on which to play and grow turfgrass. They concluded that in a "perfect" mix of the ideal combination of a uniformly graded series on non-clay particles, 25% by weight is probably the minimum clay content capable of providing sufficient strength to bind the surface of a wicket. That is, they were saying that in England clay content of 30% - 40% was ideal.

Harris (1961) had already been down the path of wicket soil research, and being Australian, had some other ideas as to the "ideal" soil. He observed that in Australia, pitch soils contain clay of 50% - 75% (as high as 82% in Perth).

The high clay content soils used in Australia and the West Indies, which potentially provide very fast pitches are, however, generally in appropriate in England due to less favorable climatic conditions for soil drying. Indeed, 1983, McIntyre, yet another soils researcher, recommended a clay content greater than 50% and if Smectite forms at least 50% of the clay minerals, then the clay content should be between 50% and 60%.

A higher clay content may cause excessive cracking, or cracks, which are too wide. If other clay minerals such as Kaolonite predominate, a greater clay content (60% - 70%) would probably improve pitch hardness.

A wicket soil with an appreciable sand fraction, particularly if coarse sand is predominate, will produce an abrasive playing surface upon which the ‘shine’ of the new ball will soon be lost, and a ‘turning’ pitch for the slow bowler may develop early in the match. McIntyre (1983) stated that coarse sand should probably be less than 10%, although the maximum tolerable is unknown.

Silt content of a wicket soil is of importance to the cohesive qualities. An excess of silt particles will reduce cohesion, and ‘powdering’ or ‘dusty’ wickets will result.

A certain amount of organic matter in the humic (colloidal) form increases plasticity, as well as improving structural stability and hydraulic conductivity. In excess it may be deleterious and an organic matter content of approximately 5% - 12% is most likely the ideal under Australian conditions.

As can be seen, the particle analysis of the wicket soils used around the world is a complex discussion and would take some further study to become more expert in understanding the ratio of particles and their interaction.

An interesting area of discussion. It is perhaps one of the most important parts of the Groundsmans’ knowledge. That is, how to produce the hard, flat, even surface required by the players. But first we have to come to terms with the ‘science’ behind it. In an attempt to offer enough so that it is comprehensible and relates to the work at hand, the following is a brief outline of the topic.

Compaction is the process of increasing soil density by packing the particles closer together.

There is a reduction in the volume of air, but no significant change in the volume of water in the soil. The degree of compaction is measured in terms of ‘bulk density’ i.e. " the mass of solids per unit volume of soil" (Craig 1983). The process of compaction must not be confused with that of consolidation.

As a thought for those who have an understanding of this subject, it can be added that the term ‘bulk density’ used by soil scientists is equivalent to the term dry density used by soil engineers.

The bulk density of a soil after compaction depends not only on the water content at the time of compaction but also on the compactive effort applied. The greater the compactive effort, a heavy roller for instance (2 tonnes maximum), the higher the maximum bulk density attainable and the lower the moisture content at which this maximum density can be achieved. For those readers who wish to know more, it is suggested that review of articles headed ‘Proctor’ compaction test is made. These tests produce a very nice ‘curve’ for further analysis.

There is a close relationship between soil bulk density and soil moisture content.

The soil moisture content determines the maximum bulk density that can be attained in a soil, and alternatively, the soil bulk density determines the maximum moisture content that can be attained in a soil.

It can be said that the higher the percentage of pitch bulk density to maximum bulk density at a given moisture content (0 –100mm pitch profile) at the commencement of play, the longer the duration time before the pitch will respond to ball spin. I.e. the higher the bulk density, the better the pitch will last.