Ruth Correll: Fall best time to soil sample

Ruth Correll • Updated Sep 12, 2018 at 8:00 AM

Although soils can be tested at any time during the year, fall is a good time to get the job done. Soils are usually drier and more accessible at this time. Also, testing in the fall allows recommended rates of lime, phosphate and potash to be applied well in advance of spring planting. 

By sampling at about the same time each year, there is less error when comparing soil test results with previous results from the same field.

Growers who follow soil test recommendations can expect higher fertilizer efficiency, more balanced nutrient levels for crops and optimum benefits from their lime and fertilizer investments. Thus, soil testing should be the first step in planning a sound fertilization program. With a soil test, the guesswork of knowing how much lime and fertilizer to apply is eliminated.

Soils should be dry enough to till when sampling. If wet samples are collected, they should be air-dried before being packaged. Wet samples are difficult to handle, and greatly delay laboratory testing. Wet samples cannot be analyzed for nitrate-nitrogen.

Soil test results are no better than the sample submitted. Each soil sample submitted should be representative of the area for which fertilizer recommendations are to be made. For field crops, a composite sample consists of small uniform portions of soil taken from approximately 20 locations over an area not to exceed 10 acres. For lawns and gardens, soil should be collected at random from eight to 10 locations and combined to make a composite sample. 

Areas of contrasting soils, problem spots, areas under different management within the same field, or portions of fields where crop response is significantly different should be sampled separately, provided the area can be fertilized separately.

Several types of tools can be used for collecting soil samples. One is the soil tube or probe or you may use a shovel or spade. It is very important to collect a “uniform” amount of soil from each random site that goes 6 inches in depth. Remove any organic debris, rocks and trash from the soil surface before collecting the sample. Collect soil from the recommended number of sites into a plastic bucket and then mix those samples thoroughly. The composite sample to be submitted to the laboratory will come from the mixed subsamples.

How often should you test your soil?  For most row crops, it is recommended to test every two years. For lawns, gardens and pastures, it is recommended every three years. You should test anytime you suspect a nutrient problem or at the beginning of a different crop rotation.

For more information, contact the UT-TSU Extension Office in Wilson County at 615-444-9584. Ruth Correll, UT Extension-TSU Cooperative Extension agent in Wilson County, may be reached at 615-444-9584 or [email protected]


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