The Nutrient Cycle - Soil: Reflections on the Basis of our Existence - page 78

The Nutrient Cycle

Compost—that sensual kingdom where
fetid waste is refined into fragrant
humus, to serve our growing friends.

Lars Krantz

Abstract The circulation of nutrients is essential to the survival of all living
things. The supply of water and oxygen, the temperature and acidity in the soil
are of great significance to this process. In a tropical rainforest, the cycle is rapid
because the temperature and humidity are just right. Nutrients are accumulated in
the vegetation rather than in the soil. In the boreal forest, the reverse is true. Low
temperatures and low pH mean that nutrients are accumulated in thick organic lay-
ers, which cause the trees to grow slowly. Experiences from natural systems can
be useful when setting up a compost heap in your own garden. Along with fact-
based texts, the chapter contains my own observations of the fascinating work of
dung beetles and coprophilous fungi. I conclude with a reflection on sustainable
gardening and how it may have been inspired by the conditions in the rainforest.

It is not easy to understand why organic matter collects in some soils and van-
ishes quickly from others. When researchers asked primary school children what
happens to fallen leaves in autumn, they found that most of the pupils understand
that leaves break down in some way or other and become part of the soil. Some
of the children reckoned that the addition of new soil every autumn ought logi-
cally to lead to the Earth growing larger. They had yet to understand that during
decomposition some matter enters a different phase and is released into the atmos-
phere as carbon dioxide, while certain minerals dissolve into liquid form in the
soil and are absorbed by plants. Likewise, many of us may not stop to think that
waste incinerated in a power station does not simply become a pile of ash, but
that most of it re-enters the atmosphere as carbon dioxide and other gases. In one
respect, though, the schoolchildren were right to suggest that the amount of soil
in the world ought to rise. For in some places, soil does indeed accumulate, albeit
slowly, if left undisturbed—and may over time grow into deep layers.

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