However, such soils are increasingly rare, and are almost non-existent in the urban environment. Typically, when sites are under construction, developers begin by removing the topsoil , - which is not just 'dirt' but is actually a complex microenvironment. Topsoil is a loose term that poorly describes the upper layers of a soil that have evolved to support an interdependent community of plants, soil-dwelling animals and microbial organisms. Developers may replace some topsoil after construction, but the site's ability to support plant growth will be drastically altered by the disturbance and compaction from heavy construction equipment. Soil amendments can be of great value in these disturbed sites.
Soil amendments can include virtually any substance that improves the growth of plants in soil.
Generally, we separate fertilizers from soil amendments by their higher nutrient content, but the distinction is not always clear since soil amendments can improve both chemical and physical properties of a soil. The chemical properties that may be altered by amendments include the soil fertility and pH. The physical properties that are improved by amendments include soil structure, porosity, and water-holding capacity. Poor soil physical characteristics directly constrain root growth and are probably the biggest problem in landscaping newly constructed sites. Improving soil physical properties . Organic soil amendments are currently the most common solution for improving physical characteristics of these sites.