The ‘Tropics Fertile Soil’ Delusion

When the first Europeans settled in South America they witnessed this abundance of dense vegetation supporting a diversity of life that never existed in Europe even prior to felling of the great forests. They reasoned that such land must be extremely fertile, but when they repeated their devastation in the new world by clearing forest, the crops were feeble and the soil exhausted. How does this contradiction exist?

A definition for permaculture (a concept of farming with nature) which I like is “thoughtful observation rather than thoughtless action”. With the benefit of hindsight this seems to be where the settlers went wrong. We can first point out that the forests of Europe feel different to the rainforests of the neotropics. In the northern temperate zone the deciduous trees blanket the ground with thick leaf litter every autumn, which decomposes to form a rich layer of humus (top soil made of essential organic matter). Not only is the leaf littler much thinner in the tropics but the frequent rains leech the soil of its fertility. So scarce are the required nutrients that the plants have evolved roots and fungal symbiosis that absorb deposits much faster than their temperate counter-parts. A study I read stated that as little as 0.1% of nutrients even penetrate to a depth of five centimetres of soil before they are sucked up.

Adding further to the settlers puzzlement was that their techniques of slash and burn to create fields were also [seemingly] being employed by the Amerindians, but were having much greater success. An observation that the Europeans failed to make was that the Amerindians lived in low-density, moving their fields regularly to allow them to rest. Whilst the idle fields lay fallow they were renewed by the detrital input of the mature forest surrounding, cultivated by the insects that come with such. Even this though was a tenuous balance of productivity and environmental devastation.

Many tropical soils lack minerals such as silicates, which are essential to build new soil. They are also often stained red with iron that exacerbate the poor retention of soil fertility and without the shade of canopy, bake into an impermeable layer. Once these fragile soils are exposed by deforestation, they die, and forest is slow to return.

To this day however, the dominating Europeans and their customs has replaced much indigenous wisdom. What must be remembered is that the fertility in the tropics is not in the soil but in the plants themselves. I encounter many farms which apply temperate methods, reasoning the misdemeanours already mentioned and wondering why they are yielding less despite the greater sun and rain. The answers lie in the methods employed before the “civilised” settlers arrival, which I will explain in a subsequent article. The sooner we can learn what was lost, the more forest that can be saved.


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