Plants need soil for anchorage and supply of minerals and water. Animals need plants for food and oxygen.
Soil is ecosystem, has complex food webs. Herbivores (plant-eaters), carnivores (meat-eaters) and detritivores (dead-organism-eaters) can be found in soil.
Other types of organisms - microscopic protozoans, fungi, nematode worms and bacteria.
Soil must contain water and oxygen to support life. All living things need water to carry out reactions in cells, cannot live without it. Almost everything needs oxygen for respiration. Roots of plants need oxygen from soil to respire.
Humus supports life in soil:
- Organic material broken down by decomposers, minerals and nutrients released into soil, compounds used by other organisms
- Humus increases air content of soil, more oxygen available for organisms
Charles Darwin studied worms, observed and experimented on what they ate and how they behaved. Discovered reasons why earthworms good for soil structure and fertility:
- They bury leaves and other organic material in soil for bacteria and fungi to decompose
- Burrows allow air to enter soil (aeration) and water to drain through. Provides soil organisms with oxygen, drainage to prevent soil becoming waterlogged (less available oxygen)
- Mix up soil layers, distribute nutrients more equally
- Soil in their faeces less acidic than soil eaten so help neutralise soil acidity (though they avoid acidic soil anyway). Acidic soil less fertile than neutral or alkaline soils
Farmers, gardeners buy earthworms to add to soil to improve it.