Consistent ball bounce is arguably the most important objective for cricket curators to achieve in the preparation of clay soil wickets. Australian cricket wickets utilize numerous clay soil types all with slightly varying properties. Studies conducted on these clay soils have characterized their properties to explain their physical behavior. Not all wicket clay soils are the same with the overriding difference being their clay mineralogy.

Clay soils used in Australia for cricket wickets are black earths. Portland, Bulli, Merri Creek and Collins wicket soils being the best known. Bulli wicket soil was first extracted in the late 1890’s from several sites near Wollongong (NSW) and was supplied by Matthew Collins to the Sydney Cricket Ground (SCG) up until the late 1950’s when the source of this supply ceased due to housing developments. Bulli soil became famous for its inherent ability to percolate water in a saturated state and to produce high quality wickets of international standard. The story of Merri Creek wicket soil in Victoria is a similar one. The original Merri Creek soil was extracted from one site in Victoria and was used at the Melbourne Cricket Club (MCG) as early as 1859 (Derriman, 1981). Collins wicket soil is a more recent type to replace another soil used around Sydney, Wamberal. What properties distinguish high quality wicket clay soils like Bulli soil and Merri Creek soil? The answer lies is their clay mineralogy.

Unlike the cricket wicket soils used in Britain and New Zealand, Australian cricket wicket soils possess less organic matter and have a greater clay content. In 1931, C. S. Piper, a soil physicist at the Waite Agricultural Research Institute (Adelaide) undertook the first survey of the physico-chemical properties of various Australian cricket wicket clay soils. Piper studied numerous clay soils which included those from Athelstone (SA), Bulli (NSW), Goodna (Qld) and Merri Creek (Vic.). Piper reported that the clay content of these soils varied between 50-75% (Piper, 1931). Subsequent studies conducted on clay soils by Don McIntyre a CSIRO soil physicist revealed more detailed properties of the clay colloids between the soils used on the major cricket grounds throughout Australia (McIntyre, 1983).

Clay mineralogy

Clay soils are composed of secondary minerals derived from primary parent rock minerals during the natural weathering processes. Most of the clay in natural soils is colloidal and which is of a crystalline structure. The crystalline structure can be seen by high-powered microscopy. The crystalline structure of clays are either of a two-layer or a three-layer. The dominant atoms are silicon and oxygen and to a lesser extent, aluminium. The degree and pattern of ‘ soil cracking’ during normal wetting and drying cycles of wickets is primarily determined by the type of clay crystalline structure. Clay minerals are basically classified into one of three clay groups. These groups being kaolinite, illite and montmorillonite (smectite). Clay mineralogy is typically determined by X-ray diffraction techniques and differential thermal analysis. Wicket soils are typically composed of each clay mineral in varying proportions. Uniformity of the cracking of the wicket surface is an inherent characteristic within the soil, based on the proportions of each clay type.

The kaolinite clay group comprises a two-layered, rigid structure that does not expand when wet. Illite has a three-layer structure and is another clay type like kaolinite, which does not expand when wet. English wicket soils are largely composed of illite and kaolinite. Montmorillinite or smectite on the other hand is a two-layer structure. Montmorillinite does have space between the layers and which expands when wet. In addition, montmorillinite clays have a greater capacity to exchange cations and which are held in the exchangeable (plant available) form (Donahue et al 1971). Both Bulli and Merri Creek soils are largely composed of smectite. Bulli and Merri Creek soils are alluvial black earths. Collins wicket soil (Sydney) is a volcanic black earth with properties which mirror those of the original Bulli soil.

Clay mineralogy results in linear and volumetric changes of clay soils, which explains their cracking ability. This is readily seen during wetting and drying cycles. High quality clay soils must possess plasticity (ability to be moulded and shaped without rupture) and maintain coherence (ability to remain dense when in a dry and moulded state). Changes in linear and volumetric shrinkage have long been used by civil engineers to characterize the structural stability of soils. Linear and volumetric shrinkage can be readily measured by laboratory methods and is a useful physical measurement to compare unknown soils in order to predict their behavior in the field. Intimate knowledge of the properties of clay soils plays a vital part of wicket preparation to achieve the desired results.

Brock, P (1997) Investigation and comparison of two cricket wicket soils at the Sydney Cricket Ground. Thesis for Associate Diploma of Applied Science. Parkville College of Tafe, Vic.
Derriman, P (1981) The Grand Old Ground - A history of the Sydney Cricket Ground. Cassell Australia
Donahue, R L, Shickman, J and Robertson, L (1971). Soils-An Introduction to Soils and Plant Growth. Prentice-Hall, Inc. USA
McIntyre, D (1983). Australian cricket pitch soils and profiles. In The National Seminar on Turf Management. RAIPR. May, 1983.
Piper, C (1931). Some characteristics of soils used for turf wickets in Australia. Trans. Royal Society South Australia. 56:15-18.