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What Happens to the Nutrients in Topsoil When it Rains?

Topsoil is that layer of dirt usually more easily dislodged than the layer of soil directly beneath it. It is often made up of the specific dirt of a region, whether sand, clay or loam, along with organic matter. While it was once thought that topsoil was a rich and healthy growing medium, the truth is that topsoil very often contains very little of the nutrients growing plants need.
  1. Erosion

    • When it rains heavily, topsoil is usually the first layer of soil to move. It is often picked up and washed into gullies, where it is deposited, creating soil "dams." In frequent and/or very heavy rains, the layer of soil beneath the topsoil may be added to the pile, as well. Unless there is organic matter growing in the topsoil, such as grass or other healthy, rooted plants, there is nothing to anchor the topsoil to the dirt below it, and it becomes a prime candidate for erosion.


    • While rain is a beneficial and necessary occurrence, there are times when it is not so beneficial for soil health. In addition to erosion, plant life suffers when heavy or frequent rains leach nutrients from the soil. This is also true of topsoil. Since topsoil drains off quickly, rains leach out the beneficial nutrients, and the topsoil usually must be amended before it can be used for growing.


    • Topsoil is easily amended to suit gardeners' needs by adding back in those nutrients that it is lacking. A soil test should be performed prior to amendment so the proper nutrients are added back in. Common amendments for topsoil are adjustments to pH through adding lime or aluminum sulphate, and adding fertilizers that contain nitrogen, potassium and phosphorous. Organic material can be added to topsoil to improve its ability to retain water and nutrients, making future amendments less frequent.

    Uses of Topsoil

    • In developing areas where the soil is largely clay, topsoil is being put to good use for lawns and gardens. It is sold bagged with the necessary amendments already added. Topsoil can also be thoroughly mixed with other soils to improve the original soil's weight, tilth and drainage.