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Leslie Carroll photo Plant testing for field crops

Procedure for sampling selected field crops


Time to sample

  • Some time between emergence and silking/pollination. Do not sample after silks have dried.

Plant part to sample

  • Seedling stage
    All above ground portion (20 to 30 plants)
  • Prior to tasseling
    The entire leaf fully developed below the whorl (15 to 25 plants)
  • Tasseling and shooting to silking
    The entire leaf at the ear node (15 to 25 plants)

Corn stalk nitrate-N

Time to sample

  • Samples should be collected at one to three weeks after 80% of the kernels reach black layer stage (physiological maturity) and not after harvest.

Plant part to sample

  • Six inch stalk samples should be cut at 6 to 8 inches above the soil surface, at black layer stage, no leaves included.
  • Preferable to sample at least a minimum of 10 stalks from the area of interest.


Time to sample

  • The ideal time is when the first bloom appears. However, if problems appear prior to bloom, a sample can be taken. Do not sample after the first pods begin to fill.

Plant part to sample

  • Seedling stage
    All the above ground portion (20 to 30 plants)
  • Prior to or during flowering
    Two or three fully developed trifoliate leaves at the top of the plant. (20 to 30 plants)

Small grain

Time to sample

  • Any time before head emerges.

Plant part to sample

  • Seedling stage
    All the above ground portion. (50 to 60 plants)
  • Prior to heading
    Select tissue from upper one third of plant. (50 to 60 plants)

Alfalfa and clovers

Time to sample

  • Just prior to bloom (1/10 bloom) or at harvest stage.

Plant part to sample

  • Take top 6 inches of plant or top 1/3 of plant. (40 to 50 plants)


Time to sample

  • Ideal time is when head is fully emerged but before pollination. Samples may be taken at earlier stage if problem develops.

Plant part to sample

  • Fully expanded and mature leaves. (15 to 25 plants)


Time to sample

  • Before bolls start to set.

Plant part to sample

  • The most recently matured leaves. (30 to 40 plants)

Submitting plant samples

The when and how of plant sampling is very dependent on the crop sampled.

Instructions for sampling and submitting samples as specified by the Columbia lab should be followed. See specific instructions on selected field crops, vegetables, and fruit crops. The recommended time to sample is just prior to the beginning of the reproductive stage for many plants. Please check the listings under the selected crops first.

  • Paired samples
    Where a deficiency is suspected, take samples from normal plants in an adjacent area as well as from the affected area. You will be charged the price of only one sample when an abnormal sample is accompanied by a normal sample. Take a soil sample from each area also.
  • Dusty plants should be avoided
    If dust is present, brushing or wiping with a clean damp cloth may be sufficient. If not, rinse briefly with water while the material is still fresh.
  • Care and handling of sample
    Air dry the sample and put in a clean paper bag or envelope and take it to the county extension Center or mail it to the lab located in Columbia.
  • Sample 25 to 30 plants throughout the area.
    Fresh plant tissue should be air dried before sending. After air drying put the sample in a clean paper bag or envelope.
  • When no specific sampling instructions are give
    The general rule of thumb is to sample upper, recently mature leaves. The recommended time to sample is just prior to the beginning of the reproductive stage for many plants.
  • Completion of the information form
    It is essential for the lab to properly interpret the plant analysis.

Where to submit plant samples

  • County extension centers
    (preferred method)
  • Soil and Plant Testing Laboratory
    23 Mumford Hall
    Columbia, MO 65211
    Phone: 573-882-0623
    Fax: 573-884-4288

Sample submitted directly to the lab should be accompanied by the sample information form and a check for the amount due payable to MU Soil Testing, unless you have an account with us. If you have an account with us fill in the firm and outlet number and we will bill you at the end of the month.

Only the lab in Columbia performs plant analysis. When submitting a sample to the lab the sample information form should be filled out accurately for the lab to properly interpret the plant analysis. Send the original form with the plant sample(s) and retain a copy for your records.

Plant analysis sample information forms can be picked up at the county extension centers or at the MU Soil and Plant Testing Laboratory free of charge or printed from the Web.
Plant analysis sample information form (RTF)

Plant analyses fees

Regular analysis
Nitrogen, phosphorus, potassium, calcium and magnesium and drying and grinding
Micro nutrients only
Copper, iron, manganese and zinc
Regular analysis plus micro nutrients
Ccopper, iron, manganese and zinc
Nitrogen (TKN) $10
Phosphorus (P) $5
Potassium (K) $5
Calcium (Ca) or Magnesium (Mg) $5
Iron (Fe) $4
Copper (Cu) $4
Manganese (Mn) $4
Zinc (Zn) $4
Total Nitrogen (N) by combustion $9
Total Carbon (C) by combustion $9
Total Sulfur (S) by combustion $9
Total C and N by combustion $16
Total N, C, S by combustion $24
Nitrate-N $8
Boron (B) $5
Chloride $6.50
Sample grinding $2
  • 10 percent discount on 30 or more samples
  • A sample preparation fee of $2 per sample will be added to all plant tissues that need to be dried and ground.
  • Testing fee for a good sample accompanying an abnormal sample will be one-half the regular price.

In the labTurnaround time

  • Soil sample analysis
    1.5 working days after samples are received in the lab
  • Plant, compost, greenhouse media and water analysis
    4 to 5 working days after samples are received in the lab

If samples are mailed allow time to and from the lab. Results of samples submitted through county extension offices are mailed first to the county agronomist or horticulturalist for comments or individualized recommendations. The county then mails the recommendations to the person submitting the sample.

Soil test reports can be emailed on request at no charge or faxed for a nominal fee.

Plant test results and interpretations

  • We use the sufficiency and survey ranges as reported in the Plant Analysis Handbook II by Harry A. Mills and J. Benton Jones, Jr. 1996. MicroMacro Publishing, Athens, Ga.

Updated 9/18/13