Topsoil is the extreme upper part of the Earth’s surface, extending downward only 2 – 12 inches (5.08 – 30.48 centimeters). It is inextricably intertwined with ecosystem stability, because it contains the necessary minerals and nutrients that living things — including the plants that directly or indirectly support thousands of species — require. Formed through natural processes, it has multiple uses and varies in terms of composition. People often add different items, such as manure, to make it more fertile and suitable for specific needs. Environmentalists have concerns about how to sustain it and keep it free from contamination.
Typically, people use topsoil to improve the quality or quantity of soil in a given area. It is most commonly used in outdoor gardens and in lawns that need reseeding. Individuals also use it in landscaping to get a specific ground level height, which is sometimes necessary to comply with specific building regulations. Many companies sell it commercially for these purposes.
This material forms when rocks are chemically or physically weathered into extremely small parts. As this happens, organic matter, such as leaves, gradually gets mixed into it, bringing nutrients such as nitrogen and that are vital to plants and microorganisms. It takes a very long time to complete this breakdown process, with one inch of topsoil taking up to 100 years to form. The slow nature of how it is made makes it important to control how much gets naturally or intentionally removed.
The way topsoil forms means that there is a wide range of combinations in terms of the percentages of sand, silt, clay, and humus it holds, with a specific makeup referred to as texture. This is not necessarily bad, because different organisms and plants often have acidity or alkaline preferences and have varying nutrient and water needs. In general, however, experts usually say that the “best” kind is the “loamy” type, which in layman’s terms means that it has a good balance of all components. True loams technically are mostly sand and silt at up to 52% and 50%, respectively, having 7 – 27% clay. They usually fall between 5.5 and 7.5 on the pH scale.
Good composition is extremely important, because it determines whether the soil will compact or spread too much. If it packs down, drainage is typically poor, and plants have a difficult time absorbing the nutrients they need to develop and stay healthy. Supporting microorganisms and other living things like worms becomes hard, because they cannot move as easily. Conversely, when it spreads, nutrients are often carried away. Most experts recommend looking for a texture that is lightweight and that breaks relatively easily after being compressed. They also advise individuals to look for darker colors, as this is often a sign that there is more organic material — and, therefore, more nutrients — in the mixture.
Although some topsoil is very fertile, it is not unusual to have to improve it a bit to get an ideal environment for growing. Many people find that they need to add some lime and fertilizer, for example. People also routinely adjust it by adding compost or manure, or by mixing in more sand, silt or clay, depending on the intended use.
Erosion is one of the biggest worries environmentalists have regarding topsoil. Loss can happen simply because it is naturally of poor quality, or because of the way geographic structures, such as sloping hillsides, make it easier for wind and water to carry it away. It also connects strongly to the idea of “exhausted soil,” however, which refers to soil that has been stripped of vital nutrients, usually from over-farming the same crops from year to year. Fewer nutrients translates to fewer plants, which means that there isn’t anything to keep the dirt from moving around.
Modern sustainable farming practices place a heavy emphasis on crop rotation to prevent soil exhaustion. Most contemporary farmers rotate their crops, allow fields to lie fallow and plant nitrogen fixing plants like beans to promote soil health. Many also plow plant material into the ground to enrich the humus, and they spread compost and manure to make it more nutritious and rich. In some areas of the world, however, farmers are working with only a few inches of topsoil and are relying on a growing collection of fertilizers to sustain crops. Desertification, which experts already are observing in Africa and Australia, can occur when no attempts are made to rejuvenate the land, and even when people take action, it can take years to repair the exhausted soil with organic practices.
In addition to being damaged by exhaustive farming practices, topsoil can also be lost through heavy water runoff. When this happens over clearcut land, matters get more complicated, because there are no trees and plants to hold the precious soil down. As a result, major storms in heavily logged areas drag tons of dirt into the watershed, where it clogs rivers and makes them uninhabitable for fish. When the rivers reach the ocean, the sudden excess of nutrients causes fish die offs which sometimes stretch for miles out to sea beyond the mouth of the river.
Another major concern with topsoil is contamination, which frequently comes from the waste created during industrial productions. Adding the wrong kind of fertilizer is also an issue, because it can make the soil unsuitable for certain types of plants and organisms. In some cases, this not only eventually results in erosion, but also poses a serious threat to health. Furthermore, seeds are not always thought of as contaminants, but they can be problematic if the plants that grow aren’t desired or are particularly invasive.