The type and composition of soil is very important in determining whether certain plants will thrive or fail. How the soil is composed affects whether minerals and nutrient compounds are able to mix with the soil, making some soils suitable for plants of all types, and other soil types relatively barren and infertile.
Organic matter is a general term for decomposing plant material. Compost of this type is generally thought to be the source of special compounds plants need to grow well. Nitrogen, phosphorus and potassium are three of the most common compounds available from organic matter, along with trace amounts of other compounds, such as carbon and magnesium.
Inorganic matter is made of small stones and rocks, and traces of metals such as iron and copper. Roughly half of all soil used for planting is inorganic in nature. Some soils, especially sandy soil, has a much higher inorganic composition, while loamy soils have almost no inorganic material at all. Along with the compounds necessary for plant life, inorganic matter also provides a fertile breeding ground for worms and insects, as well as bacteria and fungi, which promote decomposition and contribute fertilizer in the form of waste products.
Air and Water
The compounds in the soil, along with its basic composition, determine how well air and water are able to move within the soil, and those two elements regulate the microorganisms that break down plant material and keep soil healthy. For example, sandy soils are not able to retain water, and as a result the minerals and nutrients contained in sandy is easily washed away. If the soil does not appear to retain moisture, add a small amount of clay. If it tends to hold too much moisture, add 1 part sand to each 3 parts of existing soil.
Clay soil is made up of tiny particles, which are able to bond to other particles. The result is a densely packed soil that is resistant to water. The density of clay also prevents natural mixture of organic compounds into the soil, resulting in poor nutrient quality, and reduced plant vigor. Adding humus and sand to clay soil will condition it, separating the particles and mixing in vital nutrients.
Sandy soil is almost the opposite of a clay soil. Instead of tiny particles that bond together, sandy soil is made up of larger particles that do no fit well together. This loose composition means that water flows through the sand, taking minerals and nutrients with it. The result is that untreated sand is relatively low in organic compounds, and must be conditioned before plants will be able to thrive. sand can be conditioned by adding humus. If a thicker, denser soil is required, add 1 part clay for each 3 parts of sandy soil.
Loamy soil is the natural version of a compost heap. Generally found in low-lying areas, loam is formed by sediments mixing with decaying plant matter. Loamy soil is rich with microorganisms, insects and worms. These creatures promote the decomposition of plant matter, creating dark, rich soil that can be used alone, or mixed with other soil to improve its quality.