Publication Number: 452-129; Posted June 2002
your landscape into areas of unique use, i.e., a vegetable garden, lawn, perennial flower bed, etc., and to sample those unique areas individually. However, occasionally one of these unique landscape areas will be made up of one or more distinctly different soils. These soil differences may not be evident to the untrained eye, but different soils can have different chemical and physical properties which will result in differences in plant growth. You will need to take your soil sample in a way that will take into account the distinctly different soils that may exist in your landscape.
Think of it this way. When a breeder seeks a pureblooded animal, two animals of the same breed are mated. If you mix two breeds you have a mix-blooded animal, one with characteristics of both breeds. So it is with a sample that contains soil from more than one soil type. The sample will reflect a mixture of the characteristics of each soil and therefore not correctly represent either particular soil. So a soil sample that results from mixing distinctly different soils may result in fertilizer and lime recommendations that might be high for one of the soil types and low for another.
How can you tell if your landscape area has uniform soils? Here are a few clues. First, you can expect differences in soils due to vastly different landscape positions, i.e., hilltops versus steep slopes versus poorly drained bottom areas as in the figure below. Sample each area separately.
A second way that different soils may be evident is by differences in soil color. As in the figure at left, a predominantly yellow topsoil will likely have different characteristics than a topsoil that is dark brown in color. The eroded area will have different characteristics than either of the other two soils.
Soil texture is a third factor that may indicate differences in soils. A sandy soil will have different properties than a loam or a clay soil. (Appendix 1 describes a method you can use to determine the texture of your soils). For most small landscapes, it will be unusual to find soils with significantly different soil textures. However, severely eroded areas and soils disturbed during building construction are two examples of how human activities may have left soils with different textures in your landscape.
A fourth factor to consider in your landscape are those areas which have had different treatments, perhaps by you or a previous landowner. For example, different treatments exist if your lawn contains two different turf types such as fescue in the front yard and bermudagrass in the back yard. Different treatments exist if you have a portion of a landscaped bed that has consistently received greater amounts of fertilizer or other soil amendment than another portion of the bed. Different treatments will result in different properties that should be accounted for by sampling the different areas separately.
What's the bottom line? To collect an accurate soil sample that is representative of your landscape, you must, as much as possible, sample from areas that are uniform. So look for changes in soil landscape position, soil color, texture, and treatments to divide areas into separate samples. If there are no evident differences, then sample by unique use areas, i.e., lawn, vegetable garden, orchard, etc.
Also, avoid yard or landscape area borders, ditch banks, old brush piles, burn sites, severely eroded areas, old building sites, fence rows, pet dropping and urine spots, etc. Since soil taken from these locations would not be typical of the soil in the rest of the landscape area, including them could produce misleading results.
Before we proceed let's check what you have learned about where to soil sample!
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In the picture to the left, how many soil samples would you need to collect for the entire landscape? Assume that the soil behind the house (the dotted line) is a loam and in front of the house it is a clay.
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