Number of subsamples
A composite soil sample is made up of a number of individual subsamples taken at random over a given area. The purpose of this is to minimize the variability that exists. This variation may have been caused by previous lime and fertilizer applications or slight soil variations.
If an insufficient number of cores are pulled for a composite sample, the sample results can be biased either too high or too low. It is recommended that a minimum of 10 to 20 cores be taken for a composite sample. Previous sampling studies have shown that the number of cores required per composite sample varies with the size of the area being sampled. For example, 20 cores were required for a 20-acre field, 15 cores for a 10-acre field, and 10 cores for a 5-acre field.
The cores should be taken at random over a section of the field or plot, and should be representative of the entire area. When all of the cores have been collected they should be thoroughly mixed together. After mixing, a sufficient amount of sample is placed in the soil sample bag to fill the bag up to the “fill line.” You may also bring soil samples to our office in a ziplock bag. At least 2 cups of soil per field is needed for a soil analysis.
When to Sample
Soil test levels will change during the year, depending on the temperature and moisture of the soil. It’s important, therefore, that samples be taken at the same time each year so results from year to year can be compared. Generally, nutrient levels will be lower during summer and fall as compared to winter and spring.
The best time to sample is one to six months prior to planting. The earlier the better if lime is needed, because lime requires several months to fully react and neutralize soil acidity. Fertilizer should be applied closer to the time the crop needs it, as recommended in the soil test report.
For most situations soils need to be tested every 2 to 3 years. However, test the soil when there is a suspected nutrient deficiency, once per crop rotation, or once every other year if the soil is fertilized and cropped intensively. Annual sampling is recommended (1) on areas where high-value cash crops such as vegetables are grown, (2) on areas testing high in P
and K where no phosphate or potash is recommended and none is applied, and (3) on areas where the annual nitrogen application rate exceeds 150 pounds of N per acre.
Soil samples should also be taken following crops where large amounts of nutrients are removed in the harvested portion of the plant, particularly silage crops, hybrid bermuda hay, and when peanut vines are used for hay.
Keep previous soil test results from individual fields and refer to them when adjusting lime and fertilizer recommendations. Large changes in pH or nutrient levels may signal that a sampling or analytical error has been made and, if not taken into
account, could lead to an improper recommendation.
Contamination
In order to prevent contamination of the sample, clean sampling tools and collection containers should be used. Do not use galvanized or brass buckets and tools. Such devices will contaminate the samples with copper and zinc. It is best to use plastic buckets and steel sampling devices. Be sure they are clean and do not have fertilizer of lime residues.
Plowed Field Sampling Procedures
Samples should be taken to the plow depth-Usually 6 inches. Fertilizer recommendations are based on a 6-inch depth.
Pasture and No-Till Fields Sampling Instructions
Pastures and no-till fields should be sampled to a depth of 4 inches. This represents the depth of active nutrient uptake, and the zone where residual fertilizer nutrients accumulate.
How to Submit Samples for Testing
A soil test is always a good starting point before investing in fertilizer or lime. For $10, our office can test your soil and provide an exact pH and nutrient analysis with recommendations on exactly how much fertilizer and lime to apply, if any is needed. Soil test results usually are processed by our lab within 8-10 days. Please follow the procedures for taking a proper soil sample in the instructions above. Two cups of soil that is representative of the area you are sampling (mixed from several spots at random) is all that is needed to send to the lab. One sample can represent up to 15 acres if taken properly.
You may bring the sample to our office in a zip lock bag anytime Monday-Friday 8 am-noon and 1-5 pm-we close for lunch from 12 pm until 1 pm. Our office is located in Dallas at 530 West Memorial Drive, Dallas GA, 30132. If you arrive after hours, there is a large green mailbox on our front porch where you may leave your sample. A staff member will contact you to process a payment over the telephone or you are welcome to leave a check (please do not leave cash). We are located next door to the Paulding Nursing Home and Rehabilitation Center. We accept cash, check, Mastercard and Visa payment. Checks should be made out to “Paulding County 4-H”. Call our office at 770-443-7616 if you have any questions.
