Effective Soil Sampling Techniques

The success or failure of soil analysis, as an aid to fertilizer application recommendations or other use, is largely dependent upon taking a representative soil sample, closely followed by the use of proper sample handling techniques.

Many years of experience and detailed field studies have shown that certain general principles must be adhered to in order to obtain representative soil samples.

A series of soil cores of equal diameter should be taken in a systematic grid pattern. Cores should be taken from those areas of the soil that will be occupied by crop plant roots.

1. The number of cores to be taken will depend upon soil uniformity, and the degree of accuracy desired. The sample submitted to the laboratory should be a sub-sample of a much larger sample of soil which has been collected throughout a portion of the field, and "bulked." In most cases, at least 25, perhaps up to 60 soil cores should be pulled per sample. The soil cores are combined in a large bucket, and thoroughly mixed. The submitted soil sample should be between 1 pint to 1 quart in dry volume measure.
2. Separate composite samples representing different segments of the soil profile or root zone should be taken.
3. Avoid contamination from soil surface materials (crop residues, manures, fertilizers, granular herbicides, etc.); also avoid mixing samples taken to represent different soil levels.
4. In areas to be sampled at successive intervals, it is important to make a map showing initial sampling points and take subsequent samples at points at a small but definite distance away from the preceding sampling point.
5. Samples should be taken with the type of fertilizer method used in mind. For example, broadcast versus in-the-seed-row banding of fertilizer. Keep in mind to take samples representative of what the crop plant root will "see" during the growing season.

The tool to use to obtain soil cores will depend upon the soil type, and condition (i.e.- wet, dry, rocky, etc.). Most often, it will be advantageous in terms of time and labor to use a 3/4 to 1 inch soil tube (Oakfield type). If the soil is stony, gravelly, sandy, or quite dry, use other equipment such as "clam-shell" type post hole digger, a bucket type soil auger, or even a shovel. Take same-size samples from different soil levels, and sub-sample from several large samples. For large acreage, take at least one sample per 4 to 8 hectares (10-20 acres) depending upon field variations.

Effective Soil Test Results Depend Upon Proper Sampling Methods