What is soil?

What is Soil?

One definition of soil is the top layer of the earth’s surface on which we depend for many vital functions. It is made up of a mixture of organic and mineral material, organisms, air and water.

Why is soil so vital?
Everything we eat, whether vegetable or animal, depends on soil or what soil grows for it’s food. Soil allows nutrients to be reused for new growth. Soil filters earth’s rainwater. Soil seems simple, but soils are complex systems, supporting a number of different elements together at any one time, in which the chemical, physical and biological properties vary over time and space.

Soil composition
Soil is a substance, we can feel it in our hands, but more correctly, it is also a ‘complex system’ which combines a number of elements. Soil CompositionThese are mineral matter, air, water and organic matter. The percentage of these interacting elements can change in relation to each other. For example, if a soil takes in a lot of rain, this can reduce the amount of air held in the soil. Soil pore’s space makes up 50% of the soil. Soil pores contain water and/or air. Soil is also made up of half solid. This includes mineral and organic matter. Air is usually about 25% of soil. But as much as 50% of soil can be made up of air. The gases in soil are oxygen, carbon dioxide and nitrogen. Oxygen is needed for respiration in animals and plant roots. Water can be 25% of soil mass. Water is vital as plants absorb it via their root hairs. The water enters the root hairs by osmosis. Some of this water which stays in the soil can be available to roots through capillary action. Mineral matter can make up 46% of soil. Mineral matter is the largest component of soil and the proportions of this defines the soil type, for example, sandy soil is sand dominant and a loam soil will have similar amounts of sand, silt and clay. Mineral matter provides texture for the soil and is derived from rock, ie sand from sandstone.

Organic matter 5%
Organic matter is any once living plant or animal that’s remains have rotted down, plus their wastes which have enriched the soil. A fully decayed leaf/animal litter makes up humus. Humus is the sticky black material that has a number of benefits for the soil. It holds small particles together, helping to form loam. It helps the soil to hold more air and more water and it improves drainage and reduces leaching.

What soil supports; life forms
It’s also amazing and hardly believable to think how much life a good soil supports. Piggybacking in a healthy soil is a huge number of fungi and bacteria which live within that soil; many earthworms, tiny bacteria and fungi.One gram of fertile soil contains more than one thousand million bacteria, and although fungi can’t be counted in the same way, it is present in similar quantities.

To get more detailed information about soil in general, go to Wikipedia’s article