Soils

Soils—More Than the “Dirt Beneath Your Feet”

Soils serve as the foundation for terrestrial ecosystems, and as such, they serve the foundation for terrestrial life.  They provide stability and nutrients to plants, habitat for microorganisms, and shelter for burrowing invertebrates and larger animals.  Soils are also an instrumental component of nutrient cycles, facilitating and/or inhibiting the decomposition of organic matter or Soil Pedonthe weathering of mineral matter.  They play a key role in water filtration—removing excess nutrients, pesticides, and pollutants from water before it reaches streams and aquifers.

Typically when we think of soils, we only consider “the matter”—the solid particles of the soil.  But, soils are dynamic, living, breathing ecosystems comprised of soil particles, air, water, organic matter, and organisms.  Viewing the soil as a complex ecosystem helps individuals and communities develop sustainable management strategies which support soil quality and resilience for future generations of terrestrial life.

                                                                                                                               Soil Pedon.  Source: www.eoearth.org 

Soil Formation                                  

In 1941, Jans Henny introduced the notion that soils form in relation to 5 formation factors: climate, organisms, relief, parent material, and time (ClORPT).  Shortly after articulating his conceptual model, he expressed dissatisfaction with it, because he felt that it limited descriptions of the formation processes.  Decades later, however, we still use Jenny’s conceptual model as a way of understanding patterns of soils we observe on the landscape—a way of explaining what we see.  Many soil scientists add one more factor to soil forming processes—the human factor.  Human activities, like cultivation,construction, pollution, and conservation, have an enormous impact on the properties of a soil.

 

Global Soils Map

 

 

Soils and Climate

The type of soil that forms in any given region is closely related to the type of climate of that region.  This relationship is related in large part to the roles temperature, moisture, and biological activity play in weathering (generation of the mineral particles that make up the soil), decomposition (breaking down of organic matter), and creation of soil structure. 

As a result, the soils which form in the tropical rainforests (Oxisols) look and behave very differently from soils that form in the boreal forests of Canada (Spodosols) or the soils that form in the prairies of the United States Midwest (Mollisols).  Soils forming in hot, wet climates experience higher rates of weathering and decomposition and higher rates of leaching (if the nutrients released by these processes are not taken up by the vegetation).  In stark contrast, the pronounced seasonal variation at middle latitudes (both in terms of temperature and moisture) allows for periods of active weathering and decomposition to alternate with inactive periods of storage and accumulation.  Given that “not all soils are equal,” it is important to learn about the soils in an area to understand more completely the types of management and conservation strategies that will be most effective for sustaining the effective function of the soil.

 

Soils in Your Local Area

A wonderful resource which will provide you with an in-depth look into the soils in your area and at your study site is the Web Soil Survey (WSS)—http://websoilsurvey.nrcs.usda.gov.  The WSS is an interactive, digital resource, provided by the National Resources Conservation Service and United States Department of Agriculture, which provides researchers, farmers, conservationists, and educators with detailed descriptions of soils found across the US.  At the WSS site, you will find background information related to soil science and the county soil surveys.  Soil surveys provide information related to soil classification, soil characteristics, land use, conservation, and the soil water cycle for the soils present in a majority of US counties.  They are an essential resource for soil management.

Prior to the mid-2000s, the surveys were only available in hardcopy format at local county offices or libraries.  Now, the surveys are available in digital format and have been linked to a GIS (Geographic Information System) which allows you to create an area of interest (AOI).  Once the AOI for your study site has been created, you can generate a series of maps based on the characteristics of the soil you are most interested in.  Simply by clicking a box, you are able to generate a visual of the spatial pattern of parameters including soil classification, permeability, land use, pH, water, and nutrients.  The WSS is a powerful tool for orienting you to the soil environment before you “enter the field.”