The science of wicket soil

As eyes turn to Bellerive Oval for the first Ashes Test ever held in Hobart, there’s plenty of speculation about how the ground, spectators and timing might affect the outcome of the match.

One thing that will be looked at a lot – but possibly not discussed as much – is the soil underfoot. What makes a good soil for playing cricket – and why is so much work poured into getting the pitch right?

“Cricket wickets are a combination of science and art, really,” says Dr Jock Churchman, a researcher in soil science who holds adjunct positions at the University of Adelaide and the University of South Australia.

“The curators know a few tricks that have not necessarily been scientifically examined. But I suspect it’s becoming more scientific.”

All sports that are played on turf have preferred soils for the activity, and plenty of work is done to maintain this soil. But cricket pitches, which play such a big role in the outcome of the match, present some of the most interesting and complicated soil science problems.

“In most sports, the main object of the soil is to provide good drainage,” says Churchman. “But it’s almost the opposite in cricket.”

Soil on the cricket pitch has some much stricter requirements than elsewhere on the field.

“It’s got to be mouldable,” says Churchman. “It’s got to be able to be flattened […] with rollers of course, and still maintain its integrity.”

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Finding a soil that is malleable enough when wet, but hard when dry, is a tricky task. Soils with high clay content are crucial, and in Australia, a particular type of clay, referred to as ‘swelling clay’, is best.

“Swelling clay soil maintains its integrity,” says Churchman. “It only cracks, it doesn’t curl up.

“Other kinds of soil, when they dry, the particles curl up and that’s not a good thing when you’re trying to get a consistent bounce of the ball.”

The catch is that if the pitch is even a little damp, this clay becomes a problem: it gets very soft, very quickly. Swelling clay is a bad idea in the UK and New Zealand, for instance, where it’s not dry enough for long enough to dry the pitch out properly. Curators there have to resort to soil with a lower clay content.

Fortunately, this isn’t an issue in Australia, leading to something of an advantage for our grounds.

“In the whole of Australia, including Tasmania, you do get enough drying in summer to be able to use what is really the ideal soil on your cricket pitches,” says Churchman.

So, even in chilly Hobart, the pitch contains a lot of clay.

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It’s possible that this dryness has become easier to achieve with the advent of drop-in pitches.

“[Drop-in pitches] have probably led to more uniformity,” speculates Churchman.

“One thing that would happen is that when you’re drying, you don’t have such a depth to dry. So that will make it easier, I guess, for the curators.”

While soil scientists have been examining cricket since the 1960s, and have provided plenty of useful insights, curators have spent decades more honing the best techniques for choosing and maintaining wicket soil.

Each cricket ground has preferred nearby locations to collect their soil from, for instance. The SCG and the MCG famously take their soils from Bulli and Merri Creek, respectively, while in Adelaide it comes from Athelstone. All of these are areas with high clay content, and now you know why: when it comes to cricket pitches, it’s the mould that matters.