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Agricultural Testing Services: Soil Sampling

Plants require nutrients and an acceptable soil pH to grow well. Soil testing is the best way to find out how much lime and fertilizer to apply based on the crop and existing field conditions.

Reasons for Soil Testing

Soil testing measures the soil's nutrient-holding capacity and provides a basis for sound land management decisions. The lime and fertilizer recommendations on the soil test report are made based on the yields desired, nutrient sufficiency levels and desired pH.

Without soil testing, managing crop nutrients is difficult due to the complex nature of their interactions with the soil. Acid soils, for example, can limit root growth and cause certain nutrients to become unavailable to plants or others to become more available at toxic levels. Unless soil acidity is corrected through liming, applying fertilizer may not achieve the desired result.

Types of Soil Tests

Noble Research Institute soils and crops consultants make all fertilizer and lime recommendations by taking into account local conditions and producer goals. Routine soil samples are analyzed for soil pH, lime requirement, nitrate nitrogen, phosphorus, potassium, calcium, magnesium, sodium, soluble salts, organic matter and calculated CEC. Other analyses are available on request.

A Strategy for Collecting Samples

Improperly collected soil samples are the weak link in the soil testing process. For test results to be useful, the sample must accurately reflect the variability and conditions in the field. A sample from a single spot cannot achieve this.

Before sampling, make a detailed map of your land. For small areas, simply draw a diagram. For large tracts, aerial photographs may be helpful.

Divide the map into individual sample areas of 40 acres or less. Assign a short, permanent sample identification name to each area that will help you remember its location.

Each sample area should consist of only one general soil type or condition. If a field varies in slope, color, drainage or texture, and if those areas can be fertilized separately, submit a separate sample for each area (Fig. 1).

If the field being sampled has been divided into sections for various crops, submit a sample for each section – even if you now plan to grow the same crop across the entire field. Areas where liming or fertilizing patterns have differed from the rest of the field should also be sampled separately. Sample problem areas separately.

When to Collect Samples

Collect and submit samples any time you can. Try to sample at the same time of year each time you sample, though, since analyses can vary depending on when samples are taken.

In most cases, it is not necessary to take soil samples every year. Usually, once every two or three years is adequate. If you are interested in carryover nitrogen analysis, this should be done annually since these levels are dynamic.

How to Collect Routine Samples

Essential tools for collecting soil samples include a plastic bucket and a shovel or a soil probe. Do not use brass, bronze or galvanized tools because they can contaminate samples with metals.

Clean the bucket and tools before collecting samples to prevent small amounts of lime and fertilizer residue from contaminating the sample and distorting test results.

Collect samples from a depth of 0 to 6 inches. If you want to collect subsoil samples as well (useful for carryover nitrogen analysis), collect an additional sample from 6 to 12 inches.

Collect soil cores with a probe at 15 to 20 random locations across a field (Fig. 1). Zigzag patterns help ensure that samples accurately reflect overall field conditions and variability. Although a soil probe is ideal, cores can be collected with a shovel as follows: remove soil forming a small hole, cut a 1-inch thick cross-section of soil from the wall of the hole to the proper sample depth, and carefully place the soil in the bucket. For additional information on collecting a soil sample, view the How to Take a Soil Sample video.

To ensure a representative sample, avoid taking cores from small areas where soil conditions differ substantially from those in the rest of the field – for example, wet spots, severely eroded areas, old building sites, fence rows, spoil banks, burn-row areas, and old woodpile or fire sites. Cores from these spots can adversely influence soil test results and recommendations.

For each sample, collect and thoroughly mix at least 15 cores in a clean plastic bucket. From this mixture, send in about 1 pint for analysis. Provide all information requested on the Soil Sample Entry Form. Bags and forms are available on request.

Packaging and Mailing Information

Soil Sample Entry Form

Use ink when filling out the information sheet(s) and labeling soil sample bag(s). Use the appropriate sample ID from your field map. Sample bags are easier to label before they are filled.

Complete all appropriate blanks on the information sheet(s) and write legibly. Be consistent from year to year in how you list your name, farm name and/or address. List the crops you intend to grow. Also, check to make sure that the sample ID on the form corresponds to the one on the soil sample bag and on the farm map. Testing takes about seven to 10 working days to complete from the time we receive your shipment.

Place information sheets inside the shipping container with the samples and keep a copy for your records. It is a good idea to place information sheets inside a sealed plastic bag to keep them clean and legible. However, never use a plastic bag to transport and ship samples.

Do not send cash or check. When you receive your test results, you will receive an invoice from our contract laboratory for testing analysis. Servi-Tech Lab testing cost information is located in the Test Analysis Pricing document.