reliability of a soil test is only as good as the sample you submit.
The small amount of soil in the sample bag you send to the Agricultural
Testing Lab must represent the entire area to be fertilized.
Avoid unusual areas such as those where fertilizer or lime has spilled.
Take samples before lime, fertilizer, or manure are added.
Use only clean equipment for collecting soil samples.
The area to be
sampled should be as uniform as possible in terms of soil type and cropping
and fertilizing history. For practical purposes it should be an area you
expect to fertilize as a unit. This means separate samples for annual mixed
vegetables and a strawberry patch, for golf green and fairway, and for
different major crops in a commercial nursery or vegetable operation. If you
have a problem on part of a lawn, garden, or commercial production field, you
may wish to determine if soil fertility is the cause by taking one sample to
represent the “good” and the other to represent the “poor” area.
a good sample
Collect a number
of cores or slices by walking in a zigzag pattern over the area. Mix cores
thoroughly in a clean pail for a composite lab sample. The greater the number
of collected cores mixed together, the better the sample will represent the
average condition of the sampled area. Consider 10 cores as the minimum for
home gardens and lawns up to 10,000 square feet in size. Areas from a field or
sampling area of not more than 20 acres should be represented by at least 15
to 20 samples. Any area larger than 20 acres should be split for the purposes
of accurate soil testing. Choose one of the following tools:
Soil Probe or
Auger – A soil probe or auger, available from mail order catalogs and
garden or farm supply outlets, is the best tool for sampling. An auger will be
needed if the soil is very stony or gravelly. Simply push the probe (or push
and turn the auger) into the soil to the desired depth, lift up to remove the
core, and place it in the clean pail. Sampling depth should be 4 to 6 inches
deep for lawns, turf, or other perennial sod, or tillage depth (usually 6-10
inches) for annually tilled crops.
or Shovel – If a soil probe or auger is not available, collect your
sample by pushing the blade of a garden trowel, shovel, or spade into the soil
to the desired depth. Cut out a triangular wedge of soil and set it aside (to
be replaced after sampling). Now slide your blade into the soil again
taking a thin (half inch) slice from one side of the hole. With a knife,
trim the slice to about a 1-inch strip of soil down the center of the
spade-top to bottom. Save this “core” as part of your composite lab
the sample and fill the sample bag
Make sure that
all the cores are thoroughly mixed together. Wet clay soils may first require
setting aside to dry. Your soil test mailer contains a plastic bag intended
for one lab sample. Fill this bag about ½ full (approximately 1 cup) with the