The Five Soil Forming Factors are Climate, Organisms, Topography, Time, and Parent Material.
Understanding the five soil forming factors is necessary because of their importance in understanding why soils differ. Because soils are different from location to location, their productivity is also different from place to place. Soil variability also influences the environmental problems that occur in areas. Finally, using soils according to their potential will allow us to better manage our most limited resource, the soil.
An interesting web page on Soil Formation can be found at http://grunwald.ifas.ufl.edu/Nat_resources/soil_forming_factors/formation.htm
See the Diagram of Soil Forming Factors
Climate as a soil forming factor
Climate has two major components for soil formation. The first is the temperature. As the mean annual soil temperature increases, the weathering of the rocks and minerals in the soil will be faster. For every 10°C rise in temperature, the rate of biochemical reactions doubles. Thus, we find that soils weather faster in the southern U.S.A.. than in the northern states. Tropical soils will also weather faster because the chemical reactions will be taking place faster and the reactions will occur throughout the year. If all other environmental conditions are similar, the cooler the climate the greater the quantity of organic matter in the soil.
Along with temperature is the climate factor of precipitation or rainfall. In general, areas with more rainfall will have greater weathering and greater leaching. However, the amount of evapotranspiration has to be accounted for. Areas that are cool and wet will have more leaching compared to areas that are hot and wet because more of the rainfall in a hot, wet climate evaporates back into the atmosphere before leaching can occur.
In Minnesota we can use the depth of calcium carbonate (CaCO3) in
the profile to determine the leached zone of the soil. Leaching occurs when
water moves through the soil and removes the soluble constituents. The
leaching zone is determined by the location
of CaCO3 in the soil profile. This is easy to locate because calcium
carbonate reacts with hydrochloric acid (HCl) to give off carbon dioxide or the
soil bubbles when acid is applied. Soils that exhibit a leached zone are easily
determined by using this chemical test. The leached zones in the picture are
indicated with the red {.
The calcium carbonate in the soil is the white looking
material. The farther west you go in Minnesota the less the soil is leached and
the closer to the surface we find CaCO3. The thicker the leaching
zone the greater the leaching and the greater the leaching index.
A leaching index can be used to assist in
locating areas with differences in soil profiles due to climate. The leaching
index is equal to the precipitation minus the evapotranspiration.
LI=PCPT. - EVAP. Be sure to look at this
leaching index
map.
From this map the area of the state with the greatest leaching index is the Arrowhead Region of northeast Minnesota (10 to 12 inches) and the least is in the Red River Valley of northwest Minnesota (0-2 inches).
The organisms living in and on the soil respond to the climate of the area. So biotic factors and climatic factors are interrelated. Animals living in the soil can influence the soil development by their mixing activities. The mixing of the soil by organisms is called bioturbation. Humans also influence the soil with their activities of agriculture, urbanization, grazing, and forestry. Some of these changes have been negative like erosion, organic matter depletion, soil pollution, and compaction. Humans have also made soils for areas where after mining operations the landscape was destroyed. Soils have also been made when land has been reclaimed from the sea.
In Minnesota there is a direct relationship between the kind of native
vegetation and the climate of the state. In eastern Minnesota the greater
rainfall gave rise to a forest vegetation that was called the Big Woods in the
southeast (Read about theBIG WOODS in this article
from the The Minnesota Volunteer Magazine) and coniferous forest in the
northeast. In central Minnesota the vegetation was prairie-border or a mixture
of prairie and forest. In western Minnesota the vegetation was wet prairie
(wetlands) and dry prairie. The native vegetation for the maps we have today
was determined by land surveyors who recorded the vegetation on a 1 mile grid
in the late 1800s. A generalized map of the native vegetation helps to
understand how vegetation changes as you go westward in Minnesota. 
The
Minnesota DNR classifies the state into three broad eco-regions as seen on this
map. Eco-Region Map.
The different vegetation that developed on a soil will impart special
characteristics to the soil. For forested areas like the Big Woods or
coniferous forest 
the soil develops a thin surface horizon, a leached, light colored zone below
the surface, and an accumulation zone that is often brown or red in
color. 
"
Further west in Minnesota you reach the true "tall grass prairie Soils developing under a prairie vegetation will have a thick, black surface horizon, a result of the thick prairie roots contributing large amounts of organic matter to the surface soil, making it black.
In summary, climate affects the amount of leaching that takes place in the soil and the speed with which soil horizons develop. Vegetation affects the thickness and color of the surface horizons.
© Regents of the University of Minnesota, 2007 The University of Minnesota is an equal opportunity educator and employer.
Prepared by tcooper@umn.edu
