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:
  • Nitrogen
  • Phosphorus
  • Potassium for crop management purposes.
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.
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:

  1. When manure application rates are made based on Nitrogen needs - test the soil annually.
  2. When manure application rates are made based on Phosphorus needs - test the soil every 3 years.
  3. 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:

drawing of different soil tools.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*:

  1. 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.
  2. Mix the soil cores in a plastic lined bucket or soil sample bag.
  3. Send at least one pint to the lab for analysis.
  4. 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."

 

View Text-only Version Text-only Updated: 08/28/2009