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Oklahoma County Cooperative Extension Service

Soil Samples

What is a soil test? A process by which nutrients are chemically removed from the soil and measured for their plant available content within the sample. The quantity of available nutrients in the sample determines the amount of fertilizers needed for a particular crop. A soil test also measures pH and the amount of acidity within the soil to determine if lime or sulfur is needed and how much should be applied.

For instructions on how to take a soil sample click here.

 Frequently Asked Questions

How much does a Routine soil sample cost? 

$10.00 for N-P-K analysis with pH and Buffer index, includes recommendations.

( pH (1:1), Lime requirement (Sikora Buffer), NO3-N, Soil test P & K by Mehlich 3 (MIII))

Benefits of Soil Testing: The Best Management Practice

  • Increases productivity by identifying soil nutrients or soil chemical factors that are limiting plant growth;
  • Increases fertilizer use efficiency by indicating appropriate rates for different soils and crops;
  • Protects the environment by preventing over fertilization when recommendations are followed;
  • Identifies polluted or contaminated soils.

How often should a soil be tested?

A soil test should be conducted if fertilizer is going to be applied or when problems occur during the growing season. Once every year is recommended when nitrogen fertilizer is applied, and at least once every three years if P and K are concerned.

 When is the best time to take soil samples?

Soil samples can be taken anytime throughout the year for checking pH, phosphorus and potassium status.  Collect soil samples 1-2 months before planting. Early spring is a good time to take soil samples for summer crops, and summer is a good time to sample for fall and winter crops.  This allows time for lime recommended to react with the soil and change the pH before the crop is planted. To assess soil available nitrogen, sample as close to planting as possible. For Lawns, the late spring (May) is a good time sample for warm season grass and the summer (mid-Aug) is good for cool-season grasses.

What tools and supplies are needed to take a soil sample?

A clean plastic bucket, a soil probe or a shovel are needed.  Soil probes may be borrowed from our office.

Soil Sample Probe

 

How should a soil sample be taken?

Collect a core with a probe, or a slice with a shovel, of soil from the surface to 6 inches deep from 15 random locations across the sampling area. Mix the samples together in a clean plastic bucket. Put 2 cups of the mix into a soil sample bag or a clean container and label it. ( e.g., FRONT, BACK, SIDE of the house.)

 For most garden areas one sample/plot should be adequate. When you return the sample to the Extension Office specify the crop you wish to grow and the yield goal (lawn, garden, and legume crops do not need yield goal). 

For more information please check PSS-2207 How to Collect a Good Soil Sample.

Soil Sample Collecting

Several separated samples may be needed from a yard to reflect the different uses.


Can samples be taken when soils are wet?

Soil moisture does not affect the test results since samples are dried before they are analyzed.  However, extremely wet soils are difficult to collect and mix.  Therefore, allow soils to drain before sampling.  Soils too dry are normally hard to get to the right depth.

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