Floods Steal Precious Topsoil?

According to journalist Peter Sheehan writing in today’s Sydney Morning Herald:

“The rivers have been running brown. A lot of the lifeblood of this country has been gushing away in liquid mountains we don’t even see.  A few sages warned that the worst thing that could happen to Australia after a decade of drought was sustained rain…

In the piece Mr Sheehan goes on to repeat many of the myths about Australian farming.  What he doesn’t mention is that farming practices have significantly improved over recent decades.  Indeed once upon a time sugarcane farmers in Queensland used to crop the hillsides and then burn the residue before harvest.  Now they only farm the flats and mulch as they harvest through a process known as ‘green cane trash blanketing’.  

And certainly the Fitzroy Catchment was not drought ravaged when the recent floods hit, which may explain why relative to past flood, Bill Burrows, in a recent post at this blog, described the current flood as relatively “clean”.

Read the piece by Peter Sheehan here:  
http://www.smh.com.au/opinion/society-and-culture/floods-steal-precious-topsoil–and-future-goes-down-drain-20110109-19jrq.html

But then also go to the trouble of getting some perspective by reading someone who does know about farming and Australia’s top soil, I am referring to David F. Smith, former  Director-General of Agriculture for Victoria, and his article ‘Green Myths About Australian Farming’ first published at Quadrant Online here:

http://www.quadrant.org.au/magazine/issue/2009/4/green-myths-about-australian-farming

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Selective quoting from David F. Smith:

The Soils Are Old and Poor

People frequently assert that the soils of Australia are old and poor, without any idea whether this has any importance. For a start, in the southern quarter of the continent, where much of Australia’s agricultural production occurs, a considerable proportion of the area does not have old soils, but very young ones: siliceous sands, soils derived from recent basalt, and alluvial river deposits.

Often in the same breath adverse comparisons are made between the impact of agriculture on these soils and the “new” soils of Europe. In fact, it is the mode of formation more than anything that causes differences. Northern European soils are mainly derived from the widespread glaciation that dragged a variety of rocks across the landscape, grinding and mixing—but with the ice cover protecting the new soil material from leaching. The resultant plains soils of much of North America and northern Europe, while in places a bit stony, are usually of good structure, easy to cultivate, stable and fairly fertile. Present-time rainfall and river drainage is such that in Europe there is little salt accumulation. Thus while in southern Australia almost any farming system will cause some redistribution of salt which will be manifest in the landscape, in Europe salt is not likely to be evident under any system.

The other half of the assertion—that soils are poor—has more truth in it, but not a lot of importance. There are substantial areas of soil in good rainfall areas that are not poor: the modest river valleys of the Great Dividing Range, the loams of the Wimmera and the Darling Downs, the volcanic soils of the Ballarat–Trentham area, Warrnambool and in northern Tasmania. But, more importantly, there are endless examples of poor soils being made highly productive: how many young couples acquiring a new home on a barren building site on an outer suburban subdivision have built up the soil and made a garden, grown vegetables? At that scale it is straightforward, of course, usually acquiring manure and organic matter, composting garbage, nurturing the soil. Now, especially in the era of modern agricultural science, more or less the same can be, and has been, done over large areas.

It has meant researching plant nutrition and plant growth, carrying out soil analysis, then using a mixture of manufactured, so-called artificial, fertilisers to raise the level of some plant nutrients in which the soils were poor. Then, wherever possible, legume pastures and crops have been used to capture atmospheric nitrogen, and hence intercept vastly more solar energy than did the original native vegetation, and raise the organic matter level in the soil (which is different from accumulating litter on the surface). This has been done over millions of hectares, and continues. In the redgum country between Naracoorte, South Australia, and Hamilton in Western Victoria, the organic matter was raised from one to three tonnes per hectare between 1919 and 1957.

Pasture legume growth has been extraordinarily successful in southern Australia, supplying nitrogen for crops and pastures, enabling much less manufactured fertiliser to be used, which should draw praise from environmentalists. Should not Australia’s competitors be penalised for not doing the same? This success has induced a culture of belief in using natural nitrogen as far as possible, and many legume crops such as lupins, beans, lentils and peas are used in crop rotations, so we could argue for a penalty against other countries for failing to use such rotations.

Then, and perhaps even more importantly, the current emphasis on sustainability reminds us that the notion of “fertile” soil is a snare and a delusion. Nutrient removal from the soil by a crop sold, or animals grazing and producing meat or milk, must be accompanied by a replacement program. It may follow, but increasingly it is seen as best done before, or during, the growth of the crop: hydroponics is a good example. Thus initial “poorness” does not matter, and fertile soils can be seen as an opportunity to cheat—to mine the soil of its high natural fertility without noticing, at least for a time. To hear a boast that “my soil does not need artificial fertilisers” should ring an alarm bell for those interested in soil sustainability. Such people are either fortunate enough to have a large outside source of organic material, perhaps carried to the site with a large use of fossil fuel energy, and possibly being produced by running down some other soil, or they are mining their own soil.

Thus, to assert that “soils are old and poor” is not constructive in the debate about resource management, or pertinent to the future of Australia.

Forests Have Been Cut Down and Soil Movement is Massive

There has been an especially sloppy use of the word forest, which in science means “composed of trees with a trunk longer than the bole—the leafy part”. In fact much of the country cleared (especially the sand-plains in more recent decades) carried low shrubby vegetation—either they were too infertile to grow larger trees, or seeds of other species had not arrived. Building up the soil fertility means two things that matter: first, a huge increase in herbage production over large areas, with a high stocking rate of sheep and cattle, and even cash crops; and second that a wide range of trees can be grown, for example along fencelines. There is then a much greater capture of solar energy and absorption of carbon dioxide.

It is commonly asserted that soil movement and deposition of soil is 100 times what it was before European settlement, and that erosion is continuing at a great rate. An example of loose talk was the statement by James O’Loughlin, compere of the ABC television program The Inventors. In introducing the inventor of instant turf grass mats (a nylon mesh to hold the grass in place), O’Loughlin stated that this could be important because Australia has 13 per cent of the world’s erosion. Many people would link this to agriculture and our performance in managing soil for farming. And did he mean in the last year? Did he mean in the last decade? Or the last million years? What was the source of his information, and how was it measured? He should stop and think!

Current deposition may well have been calculated for a number of streams using quite precise measurements, and looking at some earlier accumulations would give some clues to the historic situation. But what is “movement”? A metre or two along the stream bed? And is counting repeated movement and deposition, as often occurs along streams, double dipping?
Measuring the past is a challenge, even using the precise dating tools available. The Murray Valley sediments in Victoria are more than 100 metres thick, laced with prior streams that were active long before the Aborigines, let alone the Europeans, arrived. When we include wind movement, we have to include the sand masses now comprising the Big and Little Deserts in Victoria, which are generally agreed to have blown inland from a south-west-facing coastline—vast quantities moving over more than 100 kilometres. It soon becomes obvious that measurement over time is impossible. Such talk is irresponsibly loose, all the more so when the Inventors film supporting the invention showed its use in protecting the batter along road construction, not stabilising a desert or preventing erosion of farmland.

It is extremely unlikely, even if a sensible calculation could be made, that the asserted figure is true or has any use at all.

An allied problem is that erosion has become a dirty word. Older people were (unemotionally) taught about the cycle of erosion—landscape formation resulting in rich deltas, beautiful gorges, plateaus, peaks.

Questioning such an assertion about soil movement is not to condone erosion. There is a need to improve and stabilise soils, as we have done over the last fifty years, to a point where the amount of erosion in Australia is far less than it was in the 1940s, possibly lower than ever before, because of human awareness.

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John Sayers requested this blog post.