RECOMMENDATIONS FOR TAKING SOIL

SAMPLES FOR FULL PROFILE TESTS

Variation in soil test results can be moderate to extreme due to nonrepresentative samples taken from a field. This variation can be due to one of the following: (1) Natural fertility variation from area to area in the fields; (2) Previous injections of fertilizer in bands; (3) Differential depletion of elements in rows verses center of rows; (4) Differential leaching of elements in irrigation furrows verses hills, etc.

Following is a sample procedure designed to average out this variation We recommend sampling at least 10 locations per field and at least 12 cores per location of the first foot. For the second foot, take 2 to 3 cores at each of the 10 locations, and for the sub soil (3, 4, 5, 6, foot) 1 core at each of the 10 locations. Each foot is kept in a separate container.

At each sample location, a line of holes should be taken perpendicular to present or previous crop rows, irrigation rills, fertilizer injection bands, etc. The line of holes should equal the spacing between rows, rills or bands. For example, if sampling is in a field previously cropped to corn with 36 inch rows, the line of 12 holes should be a hole every 3 inches for 36 inches perpendicular to the previous rows. If sampling a wheat field previously fertilized with anhydrous ammonia with 18 inch shank spacing, the line of 12 holes would be a hole every 1 1/2 inches for l8 inches perpendicular to the fertilizer injection bands.

To facilitate handling of soil after sampling the 12 cores at each sample location the soil for first foot can be mixed and reduced to l/10 volume and kept in a separate container. After sampling the 10 locations, the soil for each foot is thoroughly mixed and reduced to desired volume to send to the laboratory. For complete analyses a one-pound sample is adequate for all tests, and for a basic test only a one-half pound sample is adequate.

Sampling Soil For Micronutrient Analysis

Due to the greater possibility of contamination in soil sampling for micronutrient analysis, some special precautions are suggested:

1. Where zinc, irons or copper analyses are desired, care should be taken not to use any galvanized, soft steel, or brass equipment (sampling equipment or containers).

2. Be extremely careful to avoid any fertilizer dust contamination.

3. The safest general equipment found for micronutrient sampling consists of stainless steel soil probe, clean plastic bucket for placing and mixing soil cores, and plastic bags for drying and shipping samples. Clean cloth bags or paper sacks have been reported as being satisfactory. However, we do not recommend their use, unless plastic lined.

Sampling Soil For Nitrate And Ammonia Nitrogen

1. Rapid changes in nitrates and ammonia occur after taking a soil sample when the sample is stored moist and warm. If several days will elapse before analysis, the sample should be immediately dried at 40° - 50°C. (l00°- ll0°F) and then mailed. Normally, if wet samples arrive at the laboratory within 2-3 days changes in nitrogen is nil.

2. Deeper depth sampling is required to effectively determine the total of available nitrogen. Sampling to a 6 foot depth at 1 foot intervals is recommended where possible. See "Recommendations for taking Soil Samples for Full Profile Tests".

3. Where rill or furrow irrigation is practiced and a nitrogen test is desired, make composite samples separately for each depth. Take samples in a line at right angles to the furrow, extending one-half the distance between furrows. Take at least 12 equally spaced sample locations: for example, 3 in the furrow bottom, 6 up the shoulder, and 3 on the row crown.

4. Where banding or injection is practiced, sample as for rill irrigation.

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