Plants obtain water and nutrients from the soil surrounding their root systems. Plants also use the soil to anchor them physically, allowing them to stand upright.
Soil is made up of weathered rock fragments which contain minerals, the decaying remnants of plants and animals, including micro-organisms, and the secretions from the plants and animals living in it. It contains varying amounts of air, water and micro-organisms.
Good soil is made up of about half solids and half pores or open spaces between the solids. The solids consist of minerals and organic matter. The minerals consist of a myriad of particle sizes, from those that can be seen with the naked eye to those so small that an electron microscope is needed to view them.
These minerals make up about 45 to 48 percent of all the solid matter in soil. The remaining two to five percent is made up of organic matter.
An ideal soil would consist of the above concentrations of minerals and organic matter and the other 50 percent would include 25 percent air and 25 percent water in the porous areas.
Much of the soil in arid and semi-arid areas is almost totally devoid of decaying organic matter and macro-and micro-organisms. Without these organisms, the soil is considered "dead."
