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Natural Resources Extension Program
Testing soil for nutrient status
Soil testing is necessary to determining the current
nutrient status of soil and how much supplemental nitrogen,
phosphorus, and other nutrients are needed to meet crop
needs.
What should I sample for:
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- Nitrogen
- Phosphorus
- Potassium for crop management purposes.
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| Finding a lab to analyze
soil: |
- Look in the phone book under laboratories
that specialize in agricultural industry.
- Contact your local County Extension Office
and ask them for labs in your area.
- Contact your local NRCS Office.
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| IMPORTANT: Contact the lab that
will be running the tests before you start sampling,
to obtain specific sampling instructions. The following
steps are general sampling instructions. |
Sample frequency:
- When manure application rates are made based on
Nitrogen needs - test the soil annually.
- When manure application rates are made based on
Phosphorus needs - test the soil
every 3 years.
- Fields used for crop production are best sampled
at any time after harvest and before planting. To
obtain an accurate estimate of nitrogen availability
take samples as close to planting time as possible.
Fields with non-cultivated crops can be sampled during
the dormant season. Adequate lead-time should be allowed
for sample analysis, data interpretation, fertilizer
recommendation and actual application. To account
for seasonal variations, soil samples should be collected
at approximately the same time each year.
General
Sampling Method:
 Tool
and Materials:
Common tools used to sample soils for routine
analysis include: spade, hand probe, hand auger, bucket
auger, Oakfield probe and King tube, or vehicle-mounted
hydraulic probe and auger.
Sampling Procedures:
It is important to obtain a representative sample of
the soil. Similar to testing manure, one sample will
not provide a true estimate of the average soil nutrient
levels. Therefore, several samples are necessary. Specialized
areas, such as dead or back furrows, manure piles, fences,
roads, eroded knolls, low areas, salty or wet spots
and other variable areas should be sampled separately
or avoided. Separate soil samples are suggested for
areas within a field that have had different crop rotation
and fertilizer treatments, or that vary in slope, texture,
organic matter and depth, as shown by soil color, plant
growth or yield.
Sample Steps*:
- Take a minimum of 8 to 10 samples randomly throughout
the field.
- For nitrogen: collect separate soil samples
at depths of 0 to 12 inches AND
12 to 24 inches.
- For phosphorus: collect soil samples at a depth
of 0 to 6 inches.
- Mix the soil cores in a plastic lined bucket or
soil sample bag.
- Send at least one pint to the lab for analysis.
- Remember: more than one composite may be needed
for fields that are large or highly variable (see
discussion above).
* Adapted, with permission, from Utah State University
Extension Service, publication "Comprehensive Nutrient
Management Planning, A 12 Step Guide."
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