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Surface runoff, a type of nonpoint source pollution, from a farm field in Iowa during a rain storm.
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 Earth's biological soil activity occurs. It also houses many organisms.


  • Importance 1
  • Classification 2
  • Evaluation 3
  • Commercial application 4
  • Erosion 5
  • See also 6
  • References 7
  • External links 8


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.


In soil classification systems, topsoil is known as the "O Horizon or A Horizon," therefore, it is the very top layer.[1]


When starting a gardening project, it is crucial to check whether or not the soil is satisfactory. Following are the desired levels of Topsoil nutrients.[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)."


A major environmental concern known as topsoil

  • USDA Electronic Field Office Technical Guide - Detailed soil conservation guides tailored to individual states/counties

External links

  • The lowdown on topsoil: It's disappearing
  • Mann, C (2008). "Our Good Earth".  
  1. ^ U.S. Department of Agriculture (USDA), Soil Survey Division Staff (1993). "Soil Survey Manual." USDA Handbook 18. Chapter 3.
  2. ^ a b Topsoil . North Carolina Department of Agriculture(July, 1995)
  3. ^ 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. [2]
  4. ^
  5. ^ "Summary Report, 2007 Natural Resources Inventory". Natural Resources Conservation Services, U. S. Department of Agriculture. December 2009. p. 97. 
  6. ^ James Smolka (May 1, 2001). "Eating Locally". Discover. Retrieved May 1, 2001. 
  7. ^ "Only 60 Years of Farming Left If Soil Degradation Continues". Scientific American. December 5, 2014. 
  8. ^ "What If the World’s Soil Runs Out?". Time. December 14, 2012. 
  9. ^ "Only 60 Years of Farming Left If Soil Degradation Continues". Scientific American. December 5, 2014. 


See also

[9][8] to form naturally. On current trends, the world has about 60 years of topsoil left.[7] and 1,000 years[6] This is of great ecological concern as one inch of topsoil can take between 500[5]

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