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All in the soil

Updated Thursday, 7th April 2011

Professor Legesse Negash talks about a project to restore a sterile landscape to a place full of life, organic matter and microorganisms

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All in the Soil

Prof Legesse Negash, Addis AbabaUniversity

Founder and Leader, Centre for Indigenous Trees

Professor Legesse Negash

Well this was a spot when about five years ago there was a pile of tarmac from an old highway, and we removed this tarmac and planted it with a number of indigenous tree species, as you can see, and within five years this spot has been transformed from one which was sterile to one which is full of life.  So now this was a soil which hardly had any organic matter about six years ago when we started restoring this centre.  Now you see a lot of organic matter, and possibly we can't see it, a lot of microorganisms.


So this area here had no soils really, I mean it was...

Professor Legesse Negash

Yeah, it had soils but the soils were poor.  Productivity, especially in Africa and in the third world has declined drastically, and we are putting a lot of man-made fertiliser into the soil, and I'm afraid this is not sustainable.  We are putting three major nutrient elements back into the soil, namely phosphorous, nitrogen and potassium.  What about the remaining 40 nutrient elements, like zinc, micro-nutrients?  Okay, people in the third world are becoming increasingly weak because the foods we eat are deficient in essential, critical micronutrients such as iron.  We are restoring phosphorous by planting native tress, indigenous trees, which in turn are associated with a variety of microorganisms.  It’s now more humid beneath this canopy, natural regeneration is possible here, as you can see.


So this is really exciting.  What is it, show me what we’re seeing here.

Professor Legesse Negash

Yeah this is, these are litter from hagenia abyssinica, a very important tree, thriving in mountainous regions, and so when the leaves fall to the ground, they get decomposed by a variety of microorganisms, including fungi, and they get decomposed and they release nutrients, and that’s how agriculture is sustained.  The decaying material accumulates year after year, month after month, day after months, so you have a huge, huge amount of carbon getting, accumulating in the soil, so the soil carbon is very important in sequestering carbon dioxide, not only through photosynthesis, which takes place in live leaves, but also through decomposed little dead material incorporated in the soil.  There are organisms which colonise harsher….


Like lichens…

Professor Legesse Negash

…ecosystem, like lichens, bacteria…



Professor Legesse Negash

…bryophytes, fungi.  So you need to follow the biological principles to restore a degraded ecosystem.  You need to employ biological principles, ecological principles, what treat plant where, we need to take the genetic make-up of a given tree species, where is it suitable, where is it not suitable.  So you know, just planting trees en masse anywhere is not useful.  We have noticed that there are certain indigenous trees which I think are good for combatting climate change.  One set of species is acacias.  We can grow acacias where water is limiting, we can grow acacias where the temperature is elevated.  In short, acacias are very good for restoring degraded ecosystems.  In my opinion, trees which are indigenous to an area are more useful than trees which are introduced from elsewhere in the name of fast growth and so on.  A tree which has evolved in an area, in a given landscape, has taken millions, tens of millions of years to evolve and so we have to respect this evolution.






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