Robin Tennant Wood

Professional Services - Research & Writing

  • Part 2 of a series of posts on the joy of manure in soil...

    The dirt on soil

    Back in the early years of my academic career I worked in a university department with a number of soil scientists. ‘Soilies’ are, generally speaking, affable types who wear sturdy boots and get inordinately excited about digging holes in paddocks. In their natural environment they tend not to get irritated by much, but nonetheless, I managed to annoy them by referring to their soil samples as ‘bags of dirt’. This invariably earned me a frown and a grumbled, “It’s soil. Soil. Dirt is what falls on the floor of the lab.” What, then, is soil?

    Soil is the thin layer of friable earth that covers most of the landmasses on Earth. It is a living, breathing organism. The healthier the soil, the more life it supports. Soil consists, in varying proportions, of organic material, minerals, water and air. Each of these provides nutrients to enable the soil to continue to live and, in turn, support life.

    Organic matter consists of humus, usually the decomposed or decomposing remains of animal or vegetable material. On average, around 58% of organic matter in soil is soil organic carbon – healthy soil is a carbon sink. The organic component in soil is the basis of its fertility. Healthy soil should contain about 5% healthy soil copyorganic matter, but this varies. In Australia, alpine soils may contain up to 10%, desert soils less than 1%. It is cause for alarm, however, that in some areas, agricultural soils have dropped below that 1% mark.

    Minerals comprise the non-organic component of soil and the largest component at around 45%. These can range from silica through to clay and are usually the residue of the rock structures around and under the soil. Different regions obviously have different soil minerals depending upon the landscape and its underlying mineral structure.

    The remaining 50% of soil components are water and air, each around 20-30% depending on the soil type and surrounding conditions.

    Air provides the aerobic action necessary for the soil. Just like our skin needs to breathe, so too does the soil. Air is trapped around the particles of the soil and allows organic material to decompose, which in turn provide nutrients. Just like us, without air the soil cannot breathe and will die.

    Water is held in the soil by the organic material and acts to dissolve solutes, maintain subsoil moisture levels and regulate temperature. Soils that are low in organic matter will also be low in water content and will not retain water. Such soils may become ‘hydrophobic’, which means that water will pool and run off the surface without sinking into the soil structure.

    While a balance of all four components is necessary for soil function, for my purposes in this series of blog articles I will be focusing on the organic component, and more specifically, what we can do to enhance and maintain a healthy, productive soil.

    Our soils are currently in decline. In Australia, our soil is old. This is the oldest landmass on Earth and as such, our mountains are eroded, our rocks ancient and our topsoil layer thin. While it is easy to blame spatial and temporal geography for having thin soils of poor quality, that is a flimsy excuse. Australian soils have been, to put it bluntly, flogged to death.

    The most fertile soils, and thus the most productive agricultural regions,organicsinsoil in Australia occur along the east coast, and in the south-east and south-west corners. These areas are also, and not coincidentally, the areas with the highest annual rainfall and the highest human population density. This means that while nature took several billion years to produce a good, fertile layer of topsoil, we have taken only a couple of hundred to cover it with roads, houses, airports, factories, schools, shopping malls… Every day, on that relatively narrow strip of fertile land, urban development is encroaching on agricultural land.

    Areas that were, until recently, large farms producing food for our cities, are rapidly being subdivided into ‘rural residential’ blocks, which are not large enough to sustain agriculture and draw on urban utilities, while farming is being marginalised into the less fertile areas.

    nitrogeninsoilOne of the points of this series of blogs is to get fertility back into urban and peri-urban soils, so that food may once again be produced where the soil and rainfall is best. The other point is to provide a perspective on biowaste that views it not as something to be disposed of and which draws on resources for that disposal, but as a resource itself.

    Your soil needs you.

    Watch this space for the next post onThe tao of poo

    [Soil maps from CSIRO Soil and Landscape Grid:

  • This is Part 1 of a series of blogs entitled Pooping for the Planet. The purpose is to show how organic waste - including biosolids and manures - can be the basis of ensuring productive soils and, by extension, sustainable agriculture and food security, into the future.

    Ask not what the soil can do for you; ask what you can do for the soil.

    healthy soil copyOne of the greatest crimes committed by modern western society is that we use potable water to dispose of what is regarded as waste. Manure, dung, excrement, shit – call it what you will, but the crime is threefold: the use of precious water resources to wash away another resource that could well save the planet, thus turning both resources into pollution. What were we thinking?

    We know that human activity since the Industrial Revolution has altered not just the landscape, but the climate of the planet. Climate change is already biting hard in many parts of the globe. Extreme weather events caused by the rise in sea temperatures are devastating coastlines, while dustbowls are replacing food bowls in some countries. In the foreseeable future, droughts will become longer and drier, the sea temperature is rising, causing more frequent and stronger cyclones and hurricanes as well as coral bleaching, which in turn will wipe out some species of marine life. In Australia, our bushfire season will be extended and these events will become more frequent. Areas that are already vulnerable to climatic extremes and fluctuations will become uninhabitable. It’s too late now to stop the impact of climate change. Decisive and positive action can slow it down and mitigate its effects, but climate change is happening. It has entered a positive feedback loop where its own effects contribute to and subsequently increase those effects.

    The good news? We can offset a lot of the negative effects of climate change by reversing our one-way system of waste disposal. Yes, it really is that simple. And that complex.

    Feeding the 8 billion

    The global human population reached 7 billion in 2011. On current United Nations estimates, it will reach 8 billion in 2024 and 9 billion in 2042. This is within the life expectancy of almost everyone who is likely to be reading this now. The question is not so much where will all these people live, but what will they eat?

    According to the UN, by 2050 “it is expected that half of the world’s population growth will be concentrated in just nine countries: India, Nigeria, the Democratic Republic of the Congo, Pakistan, Ethiopia, the United Republic of Tanzania, the United States of America, Uganda and Indonesia (ordered by their expected contribution to total growth).”

    All but one of these countries are currently classified as developing countries, meaning they are economically reliant on external sources and are typically poor in agriculture. Put bluntly, by 2050, about 4.5 billion people will live in countries that are not able to support sufficient agriculture to feed themselves. Given that one of the priority goals of the UN’s Sustainable Development Program is to end hunger and develop food security and sustainable agriculture, the outlook is challenging. Sustainable agriculture needs sustainable soils.

    Soil is the Earth’s skin. Like our own skin, it can be damaged by over-exposure and needs to be nourished and protected if it is to remain healthy. We look after our own skin by eating well, limiting or abstaining from unhealthy activities, and protecting our skin from excess exposure to the sun. A healthy skin protects our bodies from infection and bacteria, assists in maintaining our body temperature, protects our blood vessels and nerve endings and minimises dehydration. The Earth’s skin performs exactly the same function.
    Healthy soil, like healthy human skin, protects the underlying structures of the Earth, such as groundwater and subsoil, from disease, dehydration and extremes of temperature. This is increasingly important as the effects of climate change become more evident. As I write this, vast tracts of California are on fire in the worst wildfire event on record. The USA has also just experienced three hurricanes in quick succession and parts of the Midwest are ravaged by drought while Ireland is being hit by a rare east-moving hurricane. Closer to home, south east Australia is in drought with no sign of rain in the short term. 

    A healthy, functioning layer of soil protects water resources and will not blow awaoperahousey during high winds during periods of drought. It’s an old joke that Australia’s biggest export to New Zealand is topsoil. During a severe dust storm in 2009, Canberra and other inland cities were blanketed in red silt, which then continued to blow eastwards to the Tasman Sea. The CSIRO estimated that at the peak of the storm, which lasted from the 22nd to the 24th September, 75,000 tonnes of topsoil were being blown off the NSW coast per hour. That’s a lot of topsoil.

    Soil also performs one other important function: it grows our food. The only way we will feed a global population of 8 billion within the next three decades, and 11 billion by the end of this century, is to ensure that the Earth’s skin remains healthy and productive.

    In Part 2 we will look at what constitutes soil and why that constitution matters.

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