DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Three compost samples on a garden soil in Norfolk, UK.The garden soil has many small stones, sand particles, and plant remains. It also contains bacteria, fungi and animals including insects, worms and molluscs. Leaf mould (left) is dark due to the presence of organic material (humus), but is poor in plant nutrients and not a good growing medium on its own. Commercial peat-based compost (right) is high in organic material, but has a low mineral content and requires artificial fertilisers to produce good plant growth. Commercial loam based compost (centre) is a mixture of mineral and organic material from loam, with added fertilisers. It lacks the coarser mineral particles characteristic of garden soil. The commercial products have been sterilised to remove animals and pathogenic micro-organisms, a process that may also kill beneficial micro-organisms that are present in natural soil.
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