Friday, 12 July 2013

The good earth series

by Robert Edis, Soil Scientist at University of Melbourne
Cross post under The Conversation Republishing guidelines.  
Australia has some of the world’s most ancient soils, many of which grow delicious produce. In this series, “The good earth”, soil scientist Robert Edis profiles some of those soils and the flavours they bring.

The good earth: peaty Black Vertosol and asparagus

The soil that grows the best asparagus in the world is the peaty Black Vertosol, in the Koo-Wee-Rup district 60km south-east of Melbourne. The most famous of these soils is the Dalmore clay – peaty phase. Many places renowned for their geo-culinary perfection are a happy mix of climate and soil factors. But in this case, it’s all about the soil.
Vertosols are those big black clayey soils – in this case more than 60% clay – that swell when wet and shrink and crack when drying out
All plants grow well in this soil and are full of flavour and nutrition. But with asparagus, very special magical things happen as the spear of the asparagus pushes through the soil to emerge at the surface for harvest. The absence of sand grains, the slipperiness of the fine clay particles (less than a thousandth of mm across) and the soft buoyancy from the peat and self-mulching mean the asparagus spear slides through the soil like a wet tongue through fairy floss. The resulting spear has the softest skin and most flavour of any, and is most prized by asparagus connoisseurs throughout the world.

The good earth: Jasmine rice and Leeton Red Sodosol

In the 1980s, it took around 3000 litres of water to grow one kilogram of rice in the Murrumbidgee Irrigation Area, NSW. Now it takes about a third of that. A big part of this reduction is thanks to the use of Sodosol soils.
Premium, fragrant Jasmine rice production around Leeton is made possible by flat topography, access to water, and, most importantly, Red Sodosols.

If Ferrosols are the Kylie Minogue of soil types, Sodosols are the Eddie McGuire. They’re in loads of places, can be annoying from time to time, and aren’t that attractive. They are sometimes described as tractor-bogging, gumboot-sucking spew (Sodosols, not Eddie).

When the soil dries it sets hard like a brick; it’s impermeable.
This impermeability makes Sodosols problematic for almost everyone. But for Leeton rice growers these soils are great. The topsoils are quite fertile, but the subsoil is highly sodic. The sodic subsoil stops water leaking from the paddy while it’s flooded. It also stops the water table rising, which would otherwise cause salinity. The less clayey and sodic topsoil, compared to most rice paddy soils, ensures production of fully matured grains, jammed pack full of flavour, nutrition and aroma.

The good earth: Green lentils and the Wimmera self-mulching Grey Vertosol 

Xcr2bq7k-1371708199Puy Lentils are little edible emeralds; their growers call them the “caviar of vegetables”.
Notwithstanding full respect and homage to the artisan cultivators of Le Puy, one cannot ignore the Wimmera, where the self-mulching Grey Vertosol soil steps up to the plate to produce Australia’s version of these premium green lentils.
Like all legumes, lentils provide their own nitrogen and even leave some in the soil, thanks to symbiotic nitrogen fixation. Bacteria live in nodules of the roots of legumes. These bacteria are able to take nitrogen from the air and convert it into a form usable by both the bacteria and the plant. This reduces the amount of fertiliser needed, for both for the lentils, and for wheat or canola planted afterwards

The good earth – King Island cheese and Currie Yellow Kurosol

Milk is very strongly and immediately influenced by what the milk producer eats. Those who remember fresh fresh cows' milk will testify to the seasonality of milk flavour, the way it changes with pasture composition.
The geology of King Island, central to the story of agriculture, is dominated by the very old (Precambrian, at more than 541 million years old) and the very young (less than around 10,000 years old). The old rocks, many of them igneous, are the parent material for the best pasture soils on the island – Yellow Kurosols.
Cheese is a great integrator of Planet Earth, and everything has to be just right. The flavour and texture components are drawn from the hands of the cheese-maker and the micro-organisms they garden, the cattle and the grass they eat, the atmosphere and water these all share, and on King Island, a Yellow Kurosol. It’s a biome on a biscuit!


The good earth: Kensington Pride mangoes and the Darwin lateritic Red Kandosol

Mpc2mshv-1372920563The earliest mangoes in Australia are Kensington Pride from the Darwin lateritic Red Kandosol starting in September.
The soils of the top end are pretty infertile, as David Adamson pointed out last week, as did Bruce Davidson last century and several folk in between. But this is sol de rigueur for mangoes. Few soils that are not rock are lousier than lateritic Red Kandosols.
The evolution of mangoes is in the deeply weathered and depleted slopes of South Asia, many with a laterite layer. It’s not so much that they don’t like deep fertile soils, its just they go a bit wild, with irregular flowering and excessive growth leading to unreliable fruit set and reduced quality, particularly in Kensington Pride. Not to mention big and hard to manage trees. This is not a problem on lateritic Red Kandosols!


The good earth: Buderim Red Ferrosol and ginger


As well as being attractive, Red Ferrosol soils produce many of Australia’s iconic foodstuffs.
One is ginger from Buderim on Queensland’s Sunshine Coast. Credited with curing everything from flatulence to nausea, ginger would be more a medicine than a food if it did not taste so delicious. The zing from ginger (it is after all in the genus Zingiber) comes from the volatile oils in the rhizome.
There is a strong regionality of ginger flavour and aroma, with the degree of pungency and lemony-ness controlled by the balance of the oils. This balance depends on the growing conditions – weather, management and, of course, soil

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