Topsoil is the top layer of the Earth's crust. Naturally created topsoil takes thousands of years to form. Topsoil is formed by the buildup of decaying organic matter and rock material broken down by climate and weather. The amount of topsoil varies based on location and type of topsoil in specific geographic locations. More than 50 million acres of cropland (rich, natural topsoil) has been lost because of wasteful farming and forestry methods. Man can mix components to create topsoil that is similar to naturally made topsoil.
There are three main types of topsoil: sand, loam and clay. To identify a type of soil, you can use a method referred to as the rope test. The rope test uses a 1-inch ball of soil in your hand that you can squeeze. Rub the soil between your fingers to try and form a small "dirt" rope. Sand is made of fine minerals; it is gritty to the touch and very porous. Sand does not hold moisture well and will crumble easily between your fingers. Loam is comprised of a combination of sand and clay. It is sticky, smooth and slick. The ball of loam will crumble easily and have a slightly gritty feel to it. Clay is formed from organic material (decayed plants) and powdered rock that was formed by glaciers moving across the world during the Ice Age. Clay is smooth and sticky (like modeling clay). Clay forms a ball that will turn into ribbons (ropes) as you squeeze it between your fingers.
Soil texture is one of three primary factors used to identify topsoil. Sandy topsoil is very porous with large air pockets between the particles. While it will absorb quite a bit of water it retains little of it and the soil dries out quickly. Loam soil is porous with fewer air pockets between particles. It can absorb and hold water well. Clay soil is very dense with few air pockets between particles. It does not absorb well and what water it does retain is usually not accessible by plants.
Organic content of topsoil is another primary factor used to identify the type of top soil available. Organic material, such as decaying plant and animal matter, influences the amount of nutrients and the ability of topsoil to retain enough water for plants to grow while still allowing water to drain preventing pooling. Sandy soil does not contain large amounts of organic material. The lack of organic content in sandy topsoil is why not many plants thrive in it. Loam topsoil has equal amounts of sand, clay and organic matter in its general composition. This makes loam topsoil highly desirable by gardeners and farmers. Clay soil is very dense and does not absorb organic material leaving it lacking in nutrient value.
pH is the measurement of hydrogen ions in a substance; the lower the number of ions, the more acidic, and the higher the number of hydrogen ions, the more alkaline or basic. It is also the third primary factor used to identify the type of topsoil you have. Rainwater affects the pH of soil. Unpolluted rainwater has a normal pH of 6 to 6.5. The organic and mineral content of the topsoil play a part in the overall pH of the soil. The higher amount of rainfall will leach elemental ions from the soil leaving behind acidic combinations of hydrogen and aluminum. Sandy soil is typically high in minerals that combine with water to form acids because it lacks organic content. Loam top soil stays close to a pH level of 7, which is considered neutral, because of the balance of organic matter and mineral content (acids and bases will neutralize each other). Clay soil is more likely to become alkaline because the minerals that make up the basic structure of clay form bases when mixed with water (ammonia and potassium).
The type of topsoil you have determines what type of plants you will be able to grow. Sandy topsoil is almost inhabitable because of its acidic nature, lack of organic matter and inability to retain moisture. There are a few plants that have adapted to this type of soil. Predominantly evergreen vines, shrubs and trees will tolerate sandy topsoil. Loam soil is preferred by a wide variety of plant species, making it the optimal topsoil for agriculture and horticulture. Clay topsoil is too compact (does not allow water absorption) and alkaline (basic) for most plants. Clay soil needs to be amended in order for vegetation to thrive. Amends include adding sand (to create a well draining soil) and organic material (adding valuable nutrients for plant growth).