The Nutrient Cycle

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.