Home » General » Soil Is Much More Than Dirt – Expert [column]

The United Nations has themed 2015 the ‘International Year of Soils’. Now, it is very easy to dismiss soil as that good-for-nothing stuff that generates dirt. This may not necessarily be true. The UN does not think so, too. As climates change, the preservation and prudent management of soils becomes of great importance, particularly in the context of sustainable food production.

In light of the Earth Day — the April 22 annual global remembrance of planet earth — and the UN’s soils theme, I got the opportunity to speak to John Wilson, a career agro-ecologist from Harare, on how best Zimbabwe can better manage its soils.

Drawing on his wealth of experience from working with small-scale farmers from across southern and eastern Africa, Wilson touched on issues such as the future of soils under climate change soils and food security in Zimbabwe and chemical use versus soil fertility.

Below is an excerpt of the interview. Jeffrey Gogo (JG) and John Wilson (JW).

JG: What is the soil?

JW: Perhaps the question should be what is the difference between living and dead soil? This is where the crux of the matter lies. In the US they use the term “dirt” for soil.

And much of their “soil” has become “dirt” because of the way they have treated it. And much ours too — seeing “dirt” as dead soil.

Soil, living soil is made up of mineral matter (the dead part) and organic matter in various stages of decay and trillionsquadrillions of micro-organisms of all sorts — the estimate goes that a teaspoon of living soil has more micro-organisms than the population of people on earth but what gets me more is that population of micro-organisms is made up of about 50 000 different species of bacteria and 8 000 species of fungi, or could be.

These are all very rough estimates but you get the idea of the extent of micro-organisms in the soil, and the diversity. It’s truly awesome.

The point to realise is that it is only really since the 1980s that science has been seriously studying the soil as living matter. Before that it was largely studied as dead matter.

Science is revealing more and more about the wonders of soil and we are only very early on our path of discovering these wonders. I’ve been mentioning numbers above but the really amazing thing in the soil is all the relationships between micro-organisms and the way they work.

JG: What is the current state of soils in Zimbabwe? Can they be relied upon to continue producing optimally, say within the next 50 years?

JW: Of course it varies from place to place but generally I would say that things are pretty bad. Ploughing was introduced here from the temperate climates of the north and has done great damage.

When soils lie bare and exposed to the sun for long periods of time (we have a long dry season) the organic matter oxidises and drops very quickly.

Research done in the 80s by the Institute of Agriculture Engineering in Hatcliffe showed that virgin clay soils that were ploughed every year dropped from about 5 percent organic matter to less than 1 percent in five or so years and virgin sandy soils from around 3 percent to less than 1 percent in around three years.

Conservation farming is trying to address this issue but we really need to develop some draft power tools (such as a chisel plough) for conservation farming if it is really going to take off.

So, I would say that unless we start farming differently the soils can’t be relied on, especially with climate change where we need more organic matter in the soil to hold moisture during long dry spells.

Furthermore, many of our range-land soils are capped hard on the surface, which means they don’t breath (and the good micro-organisms in the soil need oxygen) and also that the water runs off them and so no water going in to the soil for the micro-organisms and the plants.

And trees also play a very important part in keeping the soil healthy. Growing tobacco, while financially beneficial to some farmers in the short term, is seriously depleting our tree cover it seems.

JG: The use of chemicals, including fertilisers, has constantly been viewed as harmful to soils. Yet, when such fertilisers are applied farmers tend to produce more. In what way does the continued use of chemicals affect soil fertility? How can this be addressed?

JW: Fertilisers are a short-term measure and not sustainable. They damage the micro-organisms and acidify the soil. Fertilisers have become like a drug to the soil.

Many soils are ‘addicted’ to them and will not produce if one doesn’t use fertiliser.

These soils are largely dead. Farmers in this position cannot stop using them overnight. They need to gradually reduce their use as they also use strategies to bring the biology back into the soil. It’s not simple! But absolutely necessary.

Source : The Herald