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Field crops soil

When to sample

Nutrient levels usually vary only slightly from season to season. Soil sampling just after harvest of a high-yielding corn or soybean crop usually results in a slight depression of exchangeable potassium compared to later fall, winter or spring sampling. The best time to sample is when the acreage is lying idle: for example, summer for winter wheat or later fall and winter for spring-planted crops. Most people take soil samples in spring, just before applying fertilizer. This leaves little planning time for important fertilizer and limestone application decisions. Spring is also the time when soil testing laboratories are overloaded with samples. This will delay the return of results. Fall and winter sampling leaves more time for planning limestone and feriltizer programs for the coming year.

Field crops soil sample information form (PDF)
Soil nitrogen test form (RTF)

Field crops for which recommendations are given

Recommendations are given for the following crops -- up to 4 crops with associated yields can be selected for each sample. That is for one soil sample submitted you may get recommendations for corn at 80 bu/A, corn at 90 bu/A, corn at 100 bu/A, corn at 110 bu/A OR for one sample you may obtain recommendations for corn at 80 bu/A, soybeans at 40 bu/A, wheat at 40 bu/A, alfalfa at 3 to 7 tons per acre. So you may choose any combination of 4 crops of those crops and yields listed in the table below with the restrictions listed on yield.

Code  Crop Common yield goals
Forage establishment
1 Alfalfa or alfalfa/grass establishment 0
2 Birdsfoot trefoil/grass establishment 0
3 Clover or clover/grass establishment 0
4 Cool season grass establishment 0
5 Lespedeza/grass establishment 0
6 Overseeding legumes into grass 0
7 Warm season grass establishment 0
10 Alfalfa or alfalfa/grass hay 3 to 7 ton/A
11 Alfalfa or alfalfa/grass pasture 100 to 250 cow days/A
12 Birdsfoot trefoil/grass pasture 100 to 200 cow days/A
13 Bluegrass pasture 100 to 200 cow days/A
14 Bermudagrass hay 2 to 6 tons/A
15 Bermudagrass pasture 100 to 250 cow days/A
16 Clover or clover/grass hay 2 to 5 tons/A
17 Clover or clover/grass pasture 10 to 250 cow days/A
18 Cool season grass hay 2 to 6 tons/A
19 Cool season grass pasture 100 to 250 cow days/A
20 Cool season grass seed/hay or pasture residue 0
21 Cool season grass/stockpile fall growth 0
22 Lespedeza/grass hay 1 to 4 tons/A
23 Lespedeza/grass pasture 100 to 250 cow days/A
24 Sudangrass hay 3 to 5 tons/A
25 Sudangrass pasture 100 to 250 cow days/A
26 Warm season grass hay 2 to 5 tons/A
27 Warm season grass pasture

100 to 250 cow days/A

Row crop and small grains
100 Barley 40 to 80 bu/A
101 Buckwheat 500 to 1000 lbs/A
102 Cotton (lint) 500 to 1500 lbs/A
103 Corn (grain) 80 to 250 bu/A
104 Corn (silage) 10 to 25 tons/A
105 Wheat/Soybean double crop* 30 to 80 bu/A
106 Wheat/Sunflower double crop* 30 to 80 bu/A
107 Wheat/Grain sorghum double crop* 30 to 80 bu/A
108 Wheat/Sorghum silage double crop* 30 to 80 bu/A
109 Oats 50 to 100 bu/A`
110 Popcorn 1500 to 6000 lbs/A
111 Rice 3000 to 7000 lbs/A
112 Rye 30 to 70 bu/A
113 Grain sorghum 4000 to 10000 lbs/A
114 Sorghum silage 12 to 30 tons/A
115 Soybeans 30 to 70 bu/A
116 Sugarbeets 15 to 24 tons/A
117 Sunflowers 1200 to 2500 lbs/A
118 Tobacco 25000 to 4000 lbs/A
119 Wheat 40 to 100 bu/A
201 Southern peas 0
202 Watermelon 0
099 Idle 0

Obtaining a 6- to 7-inch core for soil samplingcHow to take a soil sample

Obtaining a 6- to 7-inch core for soil sampling.

  1. Discard organic duff on top of soil.
  2. Put 6- to 7-inch soil core in sampling bucket.
  3. Discard soil below 6 to 7 inches.


Coring tools

Coring devices are best for soil sampling. Augers are recommended on rocky soils. Hand samplers at least 3 feet long are desirable because they reduce back strain.


A power drill facilitates sampling in rocky or dry soils. Use a plastic container with a hole in the middle to collect the soil as the auger pulls it out of the ground. Empty the soil out of the plastic container into the soil sample bucket after each successful attempt to get a 6-inch core.

A well taken soil sample results in appropriate recommended rates of fertilizer and limestone.

It is best to use a soil coring device because it takes an equal amount of soil from the surface through the sampling depth (6 to 7 inches or tillage depth if deeper) and uniform soil cores at each sampling location. Soil probes and augers are available through ag companies. Your ag extension specialist may be able to help you locate a supplier. You can use a shovel, however it is not as good as a probe or auger. If you use a shovel, dig a hole to the proper depth, shave a 1-inch slice from the side of the hole and save the vertical, 1-inch wide center portion of this slice.

Collect samples from uniform areas using your field map (obtained from FSA or county soil survey). Each composite soil sample should represent uniform areas of a field and should consist of 15 to 20 separate cores. For each composite sample, avoid sampling areas with obvious differences of soil color and texture, slope, crop rotation or ferilizer, lime and manure applications. Sample differing areas separately (different composite samples). Mix individual samples (15 to 20 separate cores) to obtain one composite sample in a clean plastic pail (metal pails contaminate the soil with micronutrients) and retain 1 pint (MU soil sample box full). Soil sample boxes may be obtained free from your local University Extension center. A composite sample should not represent more than 20 acres.

Where to submit soil 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
  • Soil Testing Laboratory Delta Research Center
    P.O. Box 160
    Portageville, MO 63873
    Phone: 573-379-5431
    Fax: 573-379-5875

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.

We encourage you to submit your samples through the county extension offices. Firms or businesses may set up individual accounts with the lab to submit the samples directly.

Each sample submitted to our lab should be accompanied by an information form. These forms should be filled out accurately for proper fertilizer recommendations. Including county names is essential for us to mail the soil test results to the appropriate area agronomist or horticulturalist. This information is important to determine the soil region and to complete the soil test summary report for the state.

Samples from firms should contain the firm and outlet number for proper return of results and billing.

Send the original form with the soil sample(s) and retain a copy for your records.

Send soil samples in proper containers such as the boxes and bags specifically designed for soil samples. (Avoid glass jars, coffee cans, plastic bags, etc.) If samples are very wet, allow them to air dry for a day before mailing. Wet samples should not be sent in sample boxes that are plastic lined as they will not allow soil to dry during transit.

Copy the serial number and field/sample ID from the sample information form to the soil sample container.

Sample information forms and sample boxes can be obtained from the county extension centers or at the soil testing labs free of charge or printed from the Web.
Field crops soil sample information form (PDF)

Soil tests to request

Regular fertility tests
For a general analysis of a soil's fertility, a regular soil test package includes:

  • pH
  • Neutralizable acidity
  • Phosphorus
  • Potassium
  • Calcium
  • Magnesium
  • Organic matter
  • Cation exchange capacity

In certain cases additional tests may be required.

  • Micronutrients
    Zinc, iron, copper and manganese
    Micronutrients may be desired in high pH soils
  • Sulfur
    Sandy soils low in organic matter may have sulfur deficiency
  • Salt content
    (electrical conductivity)
    Soils with salt problems should be tested for salt content (e.g. salt or fertilizer spills, heavy applications of manure, irrigating with alkaline water, can lead to salt problems.

Soil fertility analysis tests and fees

Analysis Fee

Regular soil fertility test

  • pHs
  • Neutralizable acidity
  • Organic matter
  • Bray-1 phosphorus
  • Potassium
  • Calcium
  • Magnesium
  • Cation exchange capacity
  • Fertilizer recommendations
Secondary and minor nutrients
Zinc ($4 if run with regular or iron, manganese and copper) $5
Sulfur $4
Iron, manganese and copper $4.50
Sodium ($1.50 if run with regular) $4
Boron $5
Other special tests
Nitrate $4
Ammonium $4
Nitrate and ammonium (NO3-N and NH4-N -- Inorganic N) $7
Total exchangeable bases (Ca, Mg, K, Na) $6
Electrical conductivity $6
Chloride $6
Particle size analysis $12
pHw or pHs ($2.50 if run with regular) $4
Lime requirement (pH and N.A.) $5
Total Kjeldhal nitrogen (TKN) $12
TKN and Inorganic N and organic N $20
Total phosphorus (TP) $15
Total potassium (TK) $15
Sodium absorption ratio (SAR) $12
Exchangeable sodium percentage (ESP) $12
Base saturation (percent) $12
Bray-II phosphorus $4
Mechlich III or Olson P $4
Organic matter $5
Cation exchange capacity (addition method) $12
Setup fee, if less than five samples for special tests $20
* Walk-in rate
The fee for regular fertility tests varies in counties depending on their shipping and handling costs. Contact your county extension centetr to get the exact cost when submitting through their office.

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.

Interpreting the resulti

Interpreting the results and recommendations of soil tests

Interpretations and recommendations are based on the crops you select on the Soil Information Forms. As recommendations differ for different crops, it is important you select the cropping options you intend to plant.

The soil test results you receive will contain the following information:

  • Field information and sample ID you provided on the sample information form.
  • Soil test results
    • pHs
    • Phosphorus
    • Potassium
    • Calcium
    • Magnesium
    • Organic matter
    • Netralizable acidity
    • Calculated cation exchange capacity
    • Electrical conductivity
  • If you requested zinc, manganese, iron, copper, sodium, nitrate, ammonium, or boron these results are also given.
  • Suggested fertilizer requirements in pounds per acre for nitrogen (N), phosphorus (P2O5), and potassium (K2O), are given (zinc, and sulfur are also given if requested).
  • Lime and magnesium treatments are based on soil test levels and crop options.

Interpretations and recommendations are documented in

Updated 9/14/11