ABSTRACT
The top layer of soil, topsoil, contains organic matter that aids plant growth, but is not desirable for construction. A soil profile reveals stratifications of soil quality. Compaction caused by heavy machinery during construction degrades soil structure, reduces infiltration rates, and increases runoff and flooding. Subsoil is sometimes placed over topsoil rather than removed from the construction site. Subsoil, lacking oxygen and organic matter, is a poor medium for plant growth. Brownfields are contaminated sites that have been used for industrial purposes.
Having less than 5 percent organic matter, most soils are mineral soils. Organic soils, not suitable for construction, contain at least 30 percent organic matter.
Athletic fields are subject to compaction. Core aeration can alleviate it. To test for drainage, a percolation test may be conducted.
Nutrient cycling, whereby nutrients are broken down from complex forms to simple ones, increases the ability of soil to hold and exchange positively charged ions or cations. Many essential nutrients exist as cations. Soil humus, a substance left after organic matter has been broken down, helps soil particles “bind” together. Strands of soil-borne fungus, or hyphae, also help to bind soil particles together. A mass of hyphae, or mycelia, is visible as a white cottony substance on organic matter. A large amount of nitrogen becomes available to plants through a process known as nitrogen fixation. Nitrogen-fixing bacteria convert the gaseous form of nitrogen (N2) from inaccessible forms to forms plants can utilize.
