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General Recommendations
If a soil test is to be a reliable guide for the addition of fertilizers or lime, the sample tested must represent the soil condition of the area sampled. The specific purpose of the test must be kept in mind and the completeness of the test desired. Read and follow applicable instructions carefully; the laboratory results will tell you only what is in the sample you send. It is the sample takers responsibility to take a truly representative and unbiased sample of the field area in question.
1. Soils that differ in soil type, appearance, crop growth, or past treatment should be sampled separately, provided the area is large enough to justify fertilizing separately. A soil map can be of help in distinguishing areas and in recording location of sample.
2. Several different tools such as an augur, a soil sampling tube, or a spade may be used in taking soil samples.3. Scrape away surface litter. if an auger or a soil sampling tube is used, obtain a small portion of soil by making a boring about 7-12 inches deep, or if plowing or tilling deeper, sample to plow depth. If a tool such as a spade is used dig a V-shaped hole to sample depth; then cut a thin slice of soil from one side of the hole.4. Avoid area or conditions that are different, such as areas Where fertilizer or liming materials have spilled, gate areas where livestock have congregated, poorly drained areas, dead furrow, tillage or fertilizer corners, or fertilizer band areas of last year's crops. It is also advisable to stay at least 50 feet from barns, roads, lanes, or fence rows.
5. Because of soil variations, it is necessary that each sample consist of small portions of soil obtained from approximately 20 locations in the soil area, as illustrated by the diagram on the following page. After captaining these portions of scrip, mix them together for a representative sample.
6. If recommendations are desired, fill out the "fertilizer recommendation questionnaire" as completely as possible since this information is very important in making recommendations. Be sure the sample numbers on the "analyses requested" form correspond with the numbers on the sample bag. Where soil is very varied, and especially where land leveling has been done, or erosion and deposition are severe, the field should be checked on a Soil Variability Grid Test.
Sampling for Son Variability Grid Test
If variability proves to be great enough to be a problem in attaining uniform fertility for uniform crop response, then serious consideration should be given to mapping poor response areas as the crop grows. When the crop is off or dormant the field should be checked on an incremental or grid basis against the response map to clearly outline and determine the fertility status of poor or low areas. Then fertilization of inadequate spots should be carefully done to bring the field to a uniform fertility pattern.
When sampling for the grid, consideration should be given to carefully outlining of problem areas. This may necessitate deviating slightly from an absolutely uniform pattern. Careful grid sampling will necessitate samples from relatively small acreages (2-4 acres) and with spacing varied to check the map of known poor spots.
An example of grid sampling and mapping is shown on following page.
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