Topsoil
Topsoil as well as farm fertilizers and other potential pollutants run off unprotected farm fields when heavy rains occur.
Topsoil is the upper, outermost layer of soil, usually the top 2 inches (5.1 cm) to 8 inches (20 cm). It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. It also houses many organisms.
Importance
Plants generally concentrate their roots in and obtain most of their vital nutrients from this layer. The actual depth of the topsoil layer can be measured as the depth from the surface to the first densely packed soil layer known as subsoil.
Classification
In soil classification systems, topsoil is known as the "O Horizon or A Horizon," therefore, it is the very top layer.[1]
Evaluation
When starting a gardening project, it is crucial to check whether or not the soil is satisfactory. Different types of plants vary in their nutrient needs and preferred soil conditions, many are strongly adapted to particular conditions. However, some general guidelines for "desired levels of Topsoil nutrients" have been made, broadly suitable for many plants.[2]
| Category | Desired Results |
|---|---|
| pH Level | 5.0 to 6.2 |
| Phosphorus (P-I) | Index of 50 |
| Potassium (K-I) | Index of 50 |
| Calcium (Ca%) | 40-60% of Cation Exchange Capacity (CEC) |
| Magnesium (Mg%) | 8-10% of CEC |
| Base saturation (BS%) | 35-80% of CEC |
| Manganese (Mn-I) | Index > 25 |
| Zinc (Zn-I) | Index > 25 |
| Copper (Cu-I) | Index > 25 |
The two common types of Topsoil are Bulk and Bagged Topsoil. The following table illustrates major differences between the two.[2]
| Topsoil Type | HM%[3] | BS% | pH | P-I | K-I | Ca% | Mg% |
|---|---|---|---|---|---|---|---|
| Bulk | 0.3 | 69 | 5.2 | 009 | 026 | 45 | 10 |
| Bagged | 0.7 | 78 | 5.8 | 166+ | 178 | 56 | 12.3 |
Commercial application
A variety of soil mixtures are sold commercially as topsoil, usually for use in improving gardens and lawns, e.g. container gardens, potting soil and peat. Another important yet not commonly known use for topsoil is for proper surface grading near residential buildings such as homes. "The ground around the home should slope down six inches for the first ten feet away from the home. This can often be done by adding topsoil (not sand or gravel)."
Erosion
A major environmental concern known as topsoil erosion occurs when the topsoil layer is blown or washed away. Without topsoil, little plant life is possible. The estimated annual costs of public and environmental health losses related to soil erosion exceed $45 billion.[4] Conventional agriculture encourages the depletion of topsoil because the soil must be plowed and replanted each year. Sustainable techniques attempt to slow erosion through the use of cover crops in order to build organic matter in the soil. The United States alone loses almost 3 tons of topsoil per acre per year.[5] This is of great ecological concern as one inch of topsoil can take between 500[6] and 1,000 years[7] to form naturally. On current trends, the world has about 60 years of topsoil left.[8][9]
See also
References
- ↑ U.S. Department of Agriculture (USDA), Soil Survey Division Staff (1993). "Soil Survey Manual." USDA Handbook 18. Chapter 3.
- 1 2 Topsoil . North Carolina Department of Agriculture(July, 1995)
- ↑ Percent humic matter is a measure of the portion of organic matter that has decomposed to form humic and fulvic acids. HM% represents the portion of organic matter that is chemically reactive. This value affects determinations of lime and herbicide rates.
- ↑ http://www.ce.cmu.edu/~gdrg/readings/2007/02/20/Pimental_EnvironmentalEnergeticAndEconomicComparisonsOfOrganicAndConventionalFarmingSystems.pdf
- ↑ "Summary Report, 2007 Natural Resources Inventory". Natural Resources Conservation Services, U. S. Department of Agriculture. December 2009. p. 97.
- ↑ James Smolka (May 1, 2001). "Eating Locally". Discover. Retrieved May 1, 2001.
- ↑ "Only 60 Years of Farming Left If Soil Degradation Continues". Scientific American. December 5, 2014.
- ↑ "What If the World’s Soil Runs Out?". Time. December 14, 2012.
- ↑ "Only 60 Years of Farming Left If Soil Degradation Continues". Scientific American. December 5, 2014.
- The lowdown on topsoil: It's disappearing
- Mann, C (2008). "Our Good Earth". National Geographic Magazine 214 (3): 80–107.
External links
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Wikimedia Commons has media related to Soil science. |
- USDA Electronic Field Office Technical Guide - Detailed soil conservation guides tailored to individual states/counties