One of the classic comments that property owners like to say is: " my soil is lousy"
. However, to determine how great or mediocre your soil is you need to conduct the proper investigation of the conditions in any site to decide what plants will or will not grow. Unfortunately without the adequate investigation of soil conditions the choices made in plant selection and fertility treatments may not adequately meet the conditions that actually exist.
The National Cooperative Soil Survey identifies and maps over 20,000 different kinds of soil in the United States. Most soils are given a name, which generally comes from the locale where the soil was first mapped. Named soils are referred to as soil series. Soil survey reports include the soil survey maps and the names and descriptions of the soils in a report area. These soil survey reports are published by the National Cooperative Soil Survey and are available to everyone.
Soils are named and classified by physical and chemical properties in their horizons (layers). “Soil Taxonomy” uses color, texture, structure, and other features of the surface two meters deep to key the soil into a classification system to help people use soil information. This system also provides a common language for scientists and people making choices about plant selection and management.
Soils and their horizons differ from one another, depending on how and when they formed. Soil scientists use five soil factors to explain how soils form and to help them predict where different soils may occur. The scientists also allow for additions and removal of soil material and for activities and changes within the soil that continue each day. Soil Forming
Factors that create soils
Parent material
Few soils weather directly from the underlying rocks. These “residual”
soils have the same general chemistry as the original rocks. More commonly, soils form in materials that have moved in from elsewhere. Materials may have moved many miles or only a few feet. Windblown “loess”
is common in the Midwest. It buries “glacial till”
in many areas. Glacial till is material ground up and moved by a glacier. The material in which soils form is called “parent material.” In the lower part of the soils, these materials may be relatively unchanged from when they were deposited by moving water, ice, or wind. Sediments along rivers have different textures, depending on whether the stream moves quickly or slowly. Fast-moving water leaves gravel, rocks, and sand. Slow-moving water and lakes leave fine-textured material (clay and silt) when sediments in the water settle out.
Climate
Soils vary, depending on the climate. Temperature and moisture amounts cause different patterns of weathering and leaching. Wind redistributes sand and other particles, especially in arid regions. The amount, intensity, timing, and kind of precipitation influence soil formation. Seasonal and daily changes in temperature affect moisture effectiveness, biological activity, rates of chemical reactions, and types of vegetation.
Topography
Slope and aspect affect the moisture and temperature of the soil. Steep slopes facing the sun are warmer, just like the south-facing side of a house. Steep soils may be eroded and lose their topsoil as they form. Thus, they may be thinner than the more nearly level soils that receive deposits from areas upslope. Deeper, darker colored soils may be expected on the bottom land.
Biological factors
Plants, animals, micro-organisms, and humans affect soil formation. Animals and micro-organisms mix soils and form burrows and pores. Plant roots open channels in the soils. Different types of roots have different effects on soils. Grass roots are “fibrous”
near the soil surface and easily decompose, adding organic matter. Taproots open pathways through dense layers. Micro-organisms affect chemical exchanges between roots and soil. Humans can mix the soil so extensively that the soil material is again considered parent material. The native vegetation depends on climate, topography, and biological factors plus many soil factors such as soil density, depth, chemistry, temperature, and moisture. Leaves from plants fall to the surface and decompose on the soil. Organisms decompose these leaves and mix them with the upper part of the soil. Trees and shrubs have large roots that may grow to considerable depths.
Time
Time for all these factors to interact with the soil is also a factor. Over time, soils exhibit features that reflect the other forming factors. Soil formation processes are continuous. A recently deposited material, such as the deposition from a flood, presents no features from soil development activities. The previous soil surface and underlying horizons become buried. The time clock resets for these soils. Terraces above the active floodplain, while genetically similar to the floodplain, are older land surfaces and exhibit more development features.
These soil forming factors continue to affect soils even on “stable”
landscapes. Materials are deposited on their surface, and materials are blown or washed away from the surface. Additions, removals, and alterations are slow or rapid, depending on climate, landscape position, and biological activity.
When mapping soils, a soil scientist looks for areas with similar soil-forming factors to find similar soils. The colors, texture, structure, and other properties are described. Soils with the same kind of properties are given taxonomic names. A common soil in the Midwest reflects the temperate, humid climate and native prairie vegetation with a thick, nearly black surface layer. This layer is high in organic matter from decomposing grass. It is called a “mollic epipedon.
” It is one of several types of surface horizons that we call “epipedons.”
Soils in the desert commonly have an “ ochric”
epipedon that is light colored and low in organic matter. Subsurface horizons also are used in soil classification. Many forested areas have a subsurface horizon with an accumulation of clay called an “argillic”
horizon.
Soil Orders
Soil taxonomy at the highest hierarchical level identifies 12 soil orders. The names for the orders and taxonomic soil properties related to Greek, Latin, or other root words that reveal something about the soil. Sixty-four suborders are recognized at the next level of classification. There are about 300 great groups and more than 2,400 subgroups. Soils within a subgroup that have similar physical and chemical properties that affect their responses to management and manipulation are families.
Soil Horizons
Most naturally soil horizons have an "O,""A,""B"
and a "C"
horizons. The O horizon is at the very top and resulted from recent decomposition of organic matter. The A horizon is the fertile topsoil that in most cases of where plants derive nutrients and a lot of biological activities are occurring. The B horizons will have plant roots, and these are the areas of the soil that become critical to tree survival during excess drought conditions and anchorage. The C horizons are very limited in nutrient availability, have little to no organic matter and very low on oxygen. Many cases the soils that exist in the urban landscape today contain a large portion of C horizon soils that have mixes of A and B horizons. The A and B are buried under the C horizons. The C horizons can be made productive under proper management and treatments.
Soils In A Urban Reality
Many cases these original plotted conditions have changed due to urbanization. The horizons in many instances are inverted, and the rich plant regions of O, A, and B are buried by the C horizons. So its imperative that you anyone making decisions about fertility, plant selection, and plant management determine the chemical, physical and biological conditions of the soil in which you are managing in your landscape. The C horizons can be made productive under proper management and treatments.
Help is only a phone call away
Mark Webber's Landscaping conducts 1000' of soil tests for clients, and we advise plant owners and managers how to best manage your landscape, and what plants will or won't work in their landscaping.
https://www.webberlandscaping.com/testing-and-analysis