What Is The Role Of Plants And Animals In Soil Formation

Lesson Outline

Soils - Part 1: The Origin and Development of Soil (How Soil Gets a Life and a Proper name)

In this lesson, yous volition gain an understanding of the five soil forming factors and will be able to depict how each influences soil evolution. You will learn to identify common parent materials, determine the age of a soil, identify the types of native vegetation associated with different soils in Nebraska and define soil horizons.

[This lesson, besides every bit the other nine lessons in the Soils series, is taken from the "Soils Home Report Course," published in 1999 past the University of Nebraska Cooperative Extension.]

Soil Weathering and Soil Germination

Soil formation and development is a dynamic rather than static process. Soils were present when prehistoric animals roamed the Earth and, similar those animals, some are no longer present or are preserved merely as fossilized soils buried deep beneath our nowadays soil.

Weathering describes the means by which soil, rocks and minerals are changed by physical and chemical processes into other soil components. Weathering is an integral role of soil development. Depending on the soil-forming factors in an area, weathering may proceed quickly over a decade or slowly over millions of years.

The evolution of a soil reflects the weathering process associated with the dynamic environment in which it has formed. Five soil-forming factors accept been identified that influence the development of a specific soil. Wherever these v factors accept been the same on the landscape, the soil will be the same. Nevertheless, if i or more of the factors differ, the soils will be different. The factors are:

1.  Parent material
2.  Climate
iii.  Living organisms
four.  Topography
v.  Time

Parent Textile

Parent material is made of stone and minerals. When the other four soil-forming factors act on parent material, information technology is weathered into smaller particles forming soil.

At that place are many types of parent material with different mineral contents. The World is believed to be well-nigh iii billion years old. Mountains have been created and eroded away and so created once again. Seas have covered the land and receded leaving layers of mud, sand and lime carbonate thousands of feet thick. Volcanoes have erupted. Glaciers have formed during long periods of common cold conditions and melted during long periods of warm weather.

Parent fabric tin can be stone formed in place or the remnants of stone that was moved past wind, water, ice or even gravity. A diversity of parent material tin be found in Nebraska ranging from sand in the Sandhill Region to clays in the Missouri and other river bottoms.

In the Great Plains, specially in the due south, parent materials are primarily associated with aboriginal seas.  These seas came into the region and receded several times, leaving sediment behind, which, over time, became sandstone, limestone and shale bedrock formations.  Bedrock soil formations are classified as residual parent materials and can exist exposed and broken downward to form soil.

Figure 1.1. Cross-department of layered parent materials for southeast Nebraska, Sharpsburg-Marshall Soil Association (Elder, 1969).

In Nebraska, most residuum (e.m., limestone, sandstone and shale bedrock formations) is covered with more recent geological materials such as glacial deposits, windblown minerals or materials moved by water (Fig. 1.1). Ane or more overlying parent materials may accept been deposited in an surface area throughout fourth dimension.

Figure i.2. Surface area covered by water ice sheets.

Glacial deposits originated from great water ice sheets that moved beyond Canada and the north cardinal U.s. (Fig. one.2). Glaciers are believed to take invaded only the eastern portion of Nebraska where they filled the valleys and leveled the hills. Sand and gravel were deposited along with boulders, clay and other sediments equally the glaciers melted and retreated. Rivers which had previously flowed full of water were blocked and large amounts of sand and gravel done from the Rocky Mountains were deposited in primal Nebraska. These accumulations of sand and gravel are now the aquifers that provide our abundant supply of groundwater.

Many soils in southeastern Nebraska were formed in parent materials deposited by the glaciers, unremarkably referred to as glacial drift, glacial till or glacial outwash.

Much of the parent material deposited in ancient times has been covered by windblown fabric. The windblown silty material is called loess. It covers most of Nebraska to varying depths, except in the Sandhills and western portions of the Panhandle. This yellow-brown loess is primarily found in the subsoil zone and may exist 700 feet or more deep in the northeast and central areas of the country and simply a few feet deep in western and southeast Nebraska. Loess soils are more often than not very fertile. Some are amid the most productive soils in the world.

Windblown sand material is chosen eolian sand. It predominantly covers residuum in the Sandhills and western portions of the Panhandle. This coarse textured parent cloth is usually several feet deep and is found in both the surface and subsoil zones. Eolian soils are non very productive considering they accept very depression water-holding capacity, are depression in organic matter , and are nutrient deficient equally compared to loess soils. Most are used for grass production or natural habitat.

Geologic materials moved from the parent material past water are known as alluvium. Alluvial deposits are found in flood plain areas such as the Platte River and other stream valleys. Since stream beds constantly change over time, alluvial parent materials are highly variable as are the soils that form them.

The physical and chemical weathering processes that alter parent fabric into soil include:

• Temperature changes — freezing and thawing.
• Erosion past water, current of air, ice and gravity.
• Roots of plants, burrowing animals, insects and microorganisms.
• Water relations — wetting and drying.
• Changes in chemical composition and volume.

Physical processes primarily event in the breakdown of rocks into smaller and smaller particles. As the particles go smaller, diverse living organisms begin to accept a neat bear upon on soil formation because they contribute organic matter. In addition, the smaller particles speed chemical processes which result in new chemical compounds. All of these processes are greatly influenced by climate, especially temperature and precipitation.

Climate

Nebraska's climate is quite variable and influences soil development. Precipitation, in item, ranges from an average of 33 inches per year in southeastern Nebraska to 15 inches per year in western Nebraska (Fig. 1.3).

The amount of water inbound a soil influences the motility of calcium and other chemic compounds in the soil. Ultimately, if more chemicals are removed, the soils will exist deeper and more developed. Precipitation influences vegetation and, therefore, greatly determines the organic matter content of soils. Considering of greater precipitation in eastern Nebraska, native vegetation included luxuriant growth of the tallgrass prairie. In western Nebraska where precipitation is near half that in the east, plants of the shortgrass prairies grow much less abundantly. Thus, soil organic affair content is greater in the east than in the due west.

Higher temperatures can speed the rate of organic matter decomposition . Temperatures are typically college in the southern portion of the state than in the northern portion (Fig. i.iii). Because of this trend, organic matter content decreases from northward to south. However, the change in organic matter content from northward to south due to temperature is minuscule when compared to the modify from due east to due west due to precipitation.

Soils in eastern Nebraska commonly contain 3 percent organic matter as compared to about ane to 2 percent in the west.

Figure 1.3. Soil organic matter increases every bit you move southward and e in  the Great Plains  (Adapted from The Nature and Properties of Soils, Nyle C. Brady, ©1974, MacMillan Publishers).

Living Organisms

The almost abundant living organism in the soil is vegetation. Vegetation influences the kind of soil adult because plants differ in their root systems, size, above footing vegetative volume, food content and life bike. Soils formed under trees are profoundly different from soils formed nether grass even though other soil-forming factors are similar. Trees and grass vary considerably in their search for food and water and in the corporeality of various chemicals taken up by roots and deposited in or on summit of the soil when tree leaves and grass blades die.

Soils formed under grass are much higher in organic matter than soils formed under forests considering of their massive fibrous root structure and annual senescence of above ground vegetation. Grassland soils tend to exist darker, particularly to greater depths, and accept a more stable structure than forest soils. Soils developed under grass are generally more than fertile and best suited for crop product. Nebraska soils from any parent material are nearly all formed nether grass and, with adequate water, can be very productive.

The kind of found growing influences residue limerick. For example, the disuse products from conifer tree needles are different from those of hardwood tree leaves. These disuse products touch soil formation and development differently when water moves them through the soil.

The kind of vegetation and climate also affects the kind and numbers of other organisms that live in the soil, such as insects, pocket-sized animals, and microorganisms. Organisms chew, tear and digest plant and animal material, causing it to undergo further biochemical action as information technology decays. Nondecomposed establish and animal material may be consumed past some organisms while others feed off of organism excrements.

There are a multitude of organisms living in the soil. Included among them are mites, snails, beetles, millipedes, springtails, worms, ground squirrels, gophers, grubs, nematodes, and microorganisms (e.yard., bacteria, fungi, actinomycetes and algae). Microorganisms are the most abundant organisms in the soil.

The activity of soil organisms is strongly influenced by soil temperature, acidity and soil-h2o relations. Their major contributions to soil are improved soil structure, food transformations and fertility, aeration and enhanced productivity.

Nether forests, soil microorganisms are more diverse than under grasslands; however, microorganisms under grasslands are more active and have greater mass than under woods conditions. In general, cultivated fields have fewer organisms than virgin areas. A generalized ratio for the mass of organisms under grass/meadow:oak woods:spruce forest is 13:5:1.

Among soil organisms, bacteria are most abundant followed by actinomycete (rod-shaped microorganisms) and earthworms. Every bit much equally 4,000 pounds of leaner can be present per acre-furrow slice (furrow slice = a 6-inch depth of soil). This is more than four times the mass of earthworms that can be present.

Because of the quantity of organisms present in the soil and their ability to accelerate the decay of organic textile, they play a major role in soil formation.

Topography

Variations in topography affect moisture and temperature relations. While Nebraska is considered to be in the Neat Plains, the topography within its borders varies greatly. From a broad perspective the state tin can be divided into regions encompassing valleys, sandhills, plains, rolling hills, dissected plains, bluffs and escarpments, and valley-side slopes (see Appendix one: Topographic Regions of Nebraska). Each of these topographic regions has some mutual features which affect soil germination.

On a local scale, we tin can compare a well-nigh level field with ane that is hilly. The steeper the slope, the more influence topography has on soil development on hills and steep land. Runoff is accelerated on sloping land, so less water infiltrates the soil. Plants, therefore, tend to have shallower root systems; and less organic matter is produced, as compared to nearly level land. Steep slopes are also subjected to more erosion which removes soil equally fast, or faster, than it forms. On nearly level land, water tends to pond on the soil surface. Hither, constitute growth may exist prolific, resulting in the product of large amounts of organic matter.

Slopes with a southern exposure are warmer and drier than slopes with a northern exposure. In fact, topography affects the micro-environment for soil formation in a fashion similar to climate's affect on macro environment for soil formation.

Time

Soils have been referred to as immature, mature, and old, depending on the caste of weathering. A mature soil is in equilibrium with its environment and shows total evolution of layers or horizons in its profile (Fig. 1.4).

Soils probably never achieve equilibrium, merely they do get older and are weathering all the fourth dimension. The rate of weathering, however, slows considerably every bit the soil nears equilibrium with its surround. The longer a parent fabric has been exposed, the greater the caste of weathering and the more than developed the soil. Soils in southeast Kansas, for example, are highly weathered. Parent materials in southeast Kansas have been exposed for about 200 million years. This compares to the loess soils in Nebraska, which are but x to 50 thousand years old.

Figure 1.4. Soil contour of Holdrege silt loam, a deep, well-drained silty soil formed in loess in southcentral Nebraska.

Source: https://passel-old.unl.edu/pages/informationmodule.php?idinformationmodule=1130447038

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