I’m not kidding. The UN has declared 2015 the International Year of Soils. And not before time. Everyone should be preoccupied with dirt. I know I am.  What is going in down there, under the ground? Are my veggies growing in podzol or mycelium? Hang on, that’s soil profiles in Minecraft, not in Berowra.
The CSIRO’s recently released Soil and Landscape Grid with its 3 dimensional digital soil attribute maps could resolve most Australian gardeners’ soil questions. In case you were wondering how these maps were developed, let me put you out of your misery:
“The spatial modeling was performed using decision trees with piecewise linear models and kriging of residuals. Fifty environmental covariates that represent climate, biota, terrain, and soil and parent material were used in the modeling. Uncertainty was derived using a bootstrap (Monte Carlo-type) approach to derive for each pixel a probability density function (pdf), from which we derived 90% confidence limits”
More kriging of residuals, I say!
Gags aside, this free online resource shows why Australia needs publicly funded science and why sacking researchers in the CSIRO to bankroll Gina Rinehart’s tax breaks is a major error (if you need more persuading, CSIRO scientists also invented WiFi, Aerogard, the permanent pleat, and the word petrichor, which describes the lovely smell of damp earth after rain).
After reading about the rocks in our neck of the woods, however, I’m not sure we are best placed to fully exploit the sophisticated visualising technologies of the Soil and Landscape Grid. The geology around here is pretty danged boring. Other than the odd lens of shale, mostly on the ridge-tops (that is, under roads and houses) it’s Hawkesbury sandstone all the way down, 40 million years and 270 metres of it. Or at least, all the way down to Berowra Creek where there’s an outcrop of more fertile Narrabeen Group of shales, sandstone and clays here and there.
Of course, we’re not alone in our preposterously deep beds of sandstone. They’re on display in the Blue Mountains too, though with a few more layers clay and basalt intrusions to break up the tedium.
The humungous quantities of sandstone across a swathe of the Sydney Basin makes my sentimentality about the disappearing rock faces along the new railway cuttings of the Northern Line even more absurd. After reading about the good exposures of Ashfield Shale between Hornsbury and Beecroft, I’ve become a tiny bit obsessed with capturing the freshly exposed slices of Sydney Basin geology as they are revealed by the diggers and before they’re covered with nasty grey concrete. Wordsworth was mortified by the ugliness of railway cuttings slashing their way through the nineteenth century British countryside. Here am I mourning for disappearing railway cuttings, a slice of geological time revealed and then lost again.
Perhaps I should stop grieving the lost glories of the Pennant Hills trackwork and spend more time worrying about what my garden might be doing to the “quartz rich, nutrient poor” soils of Berowra.
My snake beans are kinda sallow – I reckon they need a side serve of well-rotted chicken manure. But even as I contemplate emptying the compost tumbler, I can’t help but fret about where my vegetable garden sits, perched above the national park with its “rich and distinctive assemblage of species that thrive on poor soils” , “60-80 different plant species growing together on an area half the size of an average house block” (Benson, Howell, McDougall, 1996, 24-5). Benson and Howell in their fascinating Taken for Granted: the bushland of Sydney and its suburbs (Kangaroo Press/Royal Botanic Gardens, 1990) mourn:
 “much of Hornsby’s rugged sandstone terrain remained undisturbed until after World War III when the increasing availability of the car and improved building technology made steeper, more remote sites available for housing. As a result, bushland on ridge-tops and upper slopes has been totally destroyed, the bush remaining only where it is virtually impossible to built, and along steep gullies which have become drainage lines. Virtually very catchment system includes some suburban development, stormwater run-off from which contains silt and nutrients. These promote weed invasion of sandstone gullies… in newer areas such at Mt Colah and Berowra [the] invasion is beginning, and the consequences appear inevitable” (108)
And that’s us, in our mid-century twentieth century house, teetering on a steep slope in a fold of the hillside you might otherwise call a creek bed. My painstakingly-made hot compost, my organic sugarcane mulch, the poo from my beloved chickens, all building nitrogen, carbon, phosphorus rich earth – garden alchemy. I’m creating an anthroposol – a human made soil – and I’m not entirely sure that’s a good thing.
As a homage to the UN’s declaration, I’ve stared in a incomprehending way at a schematic cross-section of Hawkesbury soils, I’ve thought long and hard about our B horizon (by staring even longer at this quite marvellous online introduction to soil classification – thanks again, CSIRO) and I’ve double-checked Minecraft’s definition of “podzolic” with the kids but I’m not sure how far it’s got me.
Maybe this is the chthonic thinking – thinking about the soil and the communities, plant and animal that grow from it – that my friend Kate urges us all to do in her fab blog about the Armidale Community Garden, but it’s not so much grounded me as taken me directly to Hades via the Field of Punishment. This is a special special place of suffering for people who long to understand rocks and dirt but can never remember whether the Devonian comes before or after the Carboniferous, no matter how many times they read David Johnson’s splendid Geology of Australia. And that’s without wrestling with the geopolitics of topsoil loss or the impact of international agribusiness on pesticide residues or the links between soil, country and indigenous chlthonic law…
The only solution to this torment, I feel, is another variant of subterranean thinking: that sense of mindfulness I get sitting in a darkened vehicle with a swag of empty shopping bags, gazing tranquilly at the carefully preserved, sandstone rock exposures in the underground car park of Berowra Coles.
Happy International Year of Soils everyone!
2 thoughts on “Happy International Year of Soils!”
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I find the exposed sandstone cuttings fascinating too.
If I happen to be walking past excavations for a building, I will try and get a look at the rock faces.
I went on a public tour of the tunnel boring machine for the Lane cove tunnel and it was pretty awesome.
That’s some interesting soil information you have listed too.
And good description of the geology of the Berowra Valley National Park.
I am on the Hawkesbury sandstone “soil” too, which makes edible gardening so challenging.
Halfway between the Wianamatta shale soil on the pacific highway ridge (with huge trees indicating fertile soil)
and the rich alluvial flats on the Lane cove river.
They used to have commercial fruit orchards down there.
I’m glad I’m not the only one with a love of cuttings! The tunnel experience sounds pretty cool. A friend of mine commented that driving through the completed lane cove tunnel made him feel like he was driving into the future. Quite the opposite of my cutting as past angle… You are lucky if you have some shale to grow things on – not much of that here. We have to rely on the alluvium that washes down the hill for our soil enrichment…