NMSU: Test Your Soil
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Test Your Soil

Guide A-114

Revised by C.R. Glover, Extension Agronomist
R.D. Baker, Area Extension Agronomist

College of Agricultural, Consumer and Environmental Sciences New Mexico State University

This publication is scheduled to be updated and reissued 4/05.


Soil tests provide a scientific basis for regulating available plant nutrients. Recommendations on kinds and amounts of fertilizer to apply and soil management practices are based on test results. Tests on a sample that does not accurately represent the area are likely to be misleading. The following directions can help you take a representative sample of the area you want tested.

Supplies

A soil auger, a soil tube, or a shovel and knife.

A clean bucket or other suitable container. Do not use a container made of metal.

A sample box and an information sheet, which you can get from your county agent or by writing to the Soil and Water Testing Laboratory, Box 3Q, New Mexico State University, Las Cruces, New Mexico 88003.

Where to Sample

Take a composite sample from each area or field, but as a rule, try to limit the sample area to no more than 40 acres. If you have large trouble spots or areas that differ extremely in appearance, slope, soil structure, productivity, drainage, or soil treatment, put a composite sample from each of these areas in separate sample boxes.

For a composite sample, take soil from at least five sites in a garden or lawn and up to 15 sites in a large field (as illustrated in the diagram). Avoid areas near a road, fence row, compost pile, fertilizer band, or other non-typical areas.

How to Sample

At each site remove any surface litter such as straw, leaves, and old stalks.

If you use a shovel and a knife, dig a hole about six inches deep. Take a slice of soil one-half inch thick and six inches deep and keep it on the shovel. From the center of this slice, cut a strip one-half inch wide from top to bottom and put it in the bucket. Repeat this at each site in the field.

If you use a soil auger or soil tube, take soil cores about six inches deep at each site and put in the bucket.
Mix the soil from all the sites in the same area. Place soil on a newspaper. Break any clods or lumps and let the sample dry at room temperature. Do not use heat for drying. Fill the sample box with the dry soil.
Label each sample with your name and a number keyed to a map of the area represented by each sample, so you will know where the sample was taken.

Complete the information sheet. Enclose it and the soil-testing fee in the package containing the soil sample so that all reach the laboratory together. If you send only one sample, place the information sheet and the soil-testing fee in the sample box with the soil.

The more information you can supply about the soil, the better the recommendations will be. Specify the crops that are to be grown. Fertilizer recommendations cannot be made if the crop to be grown is not specified.

Mailing the Sample

Take the soil sample box and the information sheet to your county agent, or mail them directly to the Soil and Water Testing Laboratory.

Note on Dying Plants

Grasses, vegetables, flowers, and other crops seldom die from lack of fertility. Water management, disease, and insects are some factors that can cause damage or death to plants. Check with your county agent, for soil analysis is of little value in diagnosing these problems.


New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture cooperating.

Revised April 2000
Electronic Distribution July 2000