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“Don’t Guess, Soil Test”
Soil testing is one of the most basic, yet most important steps in growing plants in Tennessee.
Testing the soil is an inexpensive method of determining the exact amount of nutrients that are
needed. When growers guess about the need for lime or fertilizers, too little or too much is likely
to be applied. By using a soil test report, the grower does not need to guess. The report will tell
exactly how much of each nutrient needs to be applied, as well as how much lime the soil
needs.
A soil test run through The University of Tennessee Soil, Plant, and Pest Center will cost you $7.
So why spend the money on getting your soil tested when you could just buy a complete
fertilizer that has nitrogen, potassium, and phosphorus and apply that? The most obvious reason
is that soil testing will promote plant growth by providing the best lime and fertilizer
recommendations. Using a complete fertilizer year after year will likely lead to a build up of
phosphorus in the soil. Testing your soil can also save you some money since it will prevent you
from spending money on lime and fertilizer that isn’t needed.
A soil test will also tell you the appropriate amount of lime to apply. When the soil pH drops
below 6.0, a number of nutrients necessary for proper growth become less available for use by
the plant. Applications of enough lime to raise the soil pH above 6.0 can increase the availability
of these nutrients, making the plants healthier and more resistant to stress. Although we are
commonly concerned with a lack of lime which causes a low pH, a high pH caused by applying
too much lime can be just as damaging as it can also lead to nutrients being less available.
When sampling farm fields, divide fields to be sampled into production areas (of 10 acres or
less) based on uniform soil type, fertilization and management history. Sandy or eroded areas
and problem areas of obviously different plant growth responses should also be sampled
separately -- provided the area is sufficiently large enough to be treated differently with lime or
fertilizer. Collect a composite soil sample by moving through the area in a zigzag pattern;
sampling at a minimum of 20 locations. This sampling procedure should be random with respect
to any existing cropping row. For determination of plant nutrients, take soil samples to a depth of
6 inches. Combine each sub-sample in a clean bucket as you move through the production area.
Thoroughly mix the sub-samples into one composite sample. From this composite sample
remove enough soil (about a cup) to fill a soil sample box. Boxes and soil test information sheets
can be obtained at the UT Extension office.
When sampling a lawn or garden, divide the area of interest into one or more sampling areas
(from about an acre down to flower bed size), based on uniform soil type, fertilization and
planting history. Collect small portions of soil from approximately 10 random locations that
represent the average soil conditions of that area. Samples should be collected to a depth of 6
inches. Be sure and mark each box and keep a record of where each sample was taken.
Having your soil tested is the only way to ensure that you are applying the correct amount of
lime and fertilizer. If you would like to pick up some soil sample boxes, or would like more
information about soil testing, stop by the UT Extension office inside the Burritt College
Building.
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