How old is topsoil

It is formed from the weathering of rocks and the subsequent addition of organic material from decaying plants and animals.

This enriches the soil and adds the nutrients essential to support plant life. The main nutrients found in topsoil are nitrogen, phosphorous, potassium and magnesium.

Nitrogen is used for growth and promotes healthy stems and leaves. Potassium and magnesium help the plants to photosynthesise, and create lush green leaves. All of these nutrients are naturally found in topsoil, but in varying quantities and quality. Soil composition and structure varies considerably from area to area and it is constantly under the influence of its environment.

People talk about having either clay or sandy soils in their gardens. Clay soils are harder to work with as they tend to harden and the nutrients are locked up in the sticky soil, although they do hold water a lot better.

Granular soils with a loamy texture make the best farmland, for example, because they hold water and nutrients well. Platy soils, regardless of texture, cause water to pond on the soil surface. Soils high in iron are deep orange-brown to yellowish-brown.

Those with lots of organic material are dark brown or black; in fact, organic matter masks all other coloring agents. Color can also tell us how a soil behaves. A soil that drains well is brightly colored.

One that is often wet and soggy has an uneven mottled pattern of grays, reds, and yellows. Soils are amazing! Life as we know it would not exist without them, as they provide countless services that benefit all humans. Clean air and water, the clothes on our backs, habitat, and food for plants and animals are just a few things we can thank soils for.

These 'goods and services' provided by soils are called ecosystem services. Breadcrumb Home About Soils. What is soil? How do soils form? Livestock often over-use these areas which results in compaction of the surface soil. South-facing slopes south aspects are warmer and dry out faster because they receive more solar heat than north-facing slopes north aspects.

This affects soil genesis because the warmer temperatures speed up most chemical reactions and increases the evaporation of water from the soil profiles. The drier nature of south aspects result in production of different natural plant communities than those on the more moist north aspects.

The shape of the topography also contributes to how the slope disperses water. Concave-shaped slopes tend to concentrate water which causes more erosion and runoff. Convex-shaped slopes tend to disperse water more uniformly. Concave positions in flatter landscapes tend to collect water and these soils are more poorly drained and may have a water table near the surface. In fact, soil climate changes quite rapidly in very short distances. Annual precipitation varies from about 7 inches in parts of the Columbia Basin to more than inches in the Olympic Rainforest.

Some areas in Washington receive very little snowfall and other areas receive many feet of snow in winter. Accumulation of snow in winter and melting of snow during the spring and summer provides runoff water in areas where precipitation is low. Great differences in temperature and in the number of frost free days also occur across Washington. Temperature changes with increases and decreases in elevation and it also changes with aspect.

Moisture and temperature differences are also evident in soil genesis. Climate directly and indirectly effects soil formation. Less development occurs in drier areas because as water quickly moves into and through a soil it increases the rate of weathering of soil materials.

For example, soluble materials such as organic matter, clay, and calcium carbonate and other salts are moved downward in a soil profile and sometimes out of a soil profile if enough water is available. In general terms, the depth at which soluble material occurs in a soil profile indicates the amount of water that the soil individual receives.

Thus a record of the average annual precipitation and average annual soil temperature on each site is important. The amount of moisture within a soil profile also impacts the soil pH.

Soil pH is a determining factor in the kinds of plants that can grow on a soil. It also affects the availability of other nutrients that plants need to grow. If a soil is wet, soil characteristics illustrate that fact. Most of these wet soils in Washington are in depressions or along rivers and streams.

Soil wetness is a concern for many uses unless the soil can be drained. Many kinds of plants and animals are not able to live on or in these soils because of the lack of soil air. However, there are plants that have adapted to life on wet soils and these plants help a soil scientist identify wet soils. Both living plants and animals including humans affect natural soil formation.

This is the reason soils at the base of slopes, and especially on flood plains are typically young. Organisms contribute especially to the development of the A horizon surface horizon or topsoil as they contribute organic matter. Beyond that, organisms do not have a great effect on the age of a soil. In general, soils in hot and humid environments like the southeastern USA or tropical rainforests tend to be more developed than soils in cooler or drier environments.

They may not be older in terms of actual time or years, but in terms of weathering of the minerals present and amount of horizon development, they are definitely older.

Exceptions to this rule occur in some deserts which are on stable landscapes, and the soils have a lot of horizon development, but it occurred in times of previous climates such as ice ages when the climate was wetter.

Little development happens in deserts because there is almost no water moving through the soil and almost no vegetation growing. In many deserts much of the topsoil has been removed due to wind or water erosion leaving a stone pavement. And you missed an important one that sometimes is related to landscapes and topography, but what kinds of parent materials are present, in other words, what is the stuff in which the soil is forming.

If the soil is forming in bedrock, the rate of soil formation is affected by the rate of weathering of the bedrock: sandstones often weather more easily than limestones or shales. Soils forming on glacial depositions cannot be any older than the time the glacier receded.

And one of my favorites to observe is in western New Mexico and Arizona, USA, where volcanic activity has left lava flows of different ages. You can look at the kind and amount of vegetation growing, and the amount and depth of weathering of the lava to determine the relative age of the flows as well as the relative ages of the soils forming in them.

Cl — Climate. These factors affect the rate of weathering of minerals, which plants grow, and how much water moves through a profile. O — Organisms.