Soil Testing for Lawns

Nicholas Held, Extension Educator, Spencer County

By this time of year, most lawns have seen their last mowing and last fertilization of the season and, with the exception of raking a few remaining leaves, there aren’t too many lawn tasks left to finish.  One task that can still be done is soil testing.  Testing the soil in the fall will allow plenty of time to get the results back and plan any fertilizer applications or other soil amendments before spring. 

Periodic testing of soil will help determine what the soil needs to nourish healthy turf and fertilizer applications should not be made without periodic soil testing.  Soil scientists recommend testing the soil in your lawn every 3 to 5 years.  Soil testing bags and forms are available at Extension Offices throughout Indiana.  

The following are some tips on soil testing and some explanations of soil testing terms:

Taking a Soil Sample

·         Contact your county Cooperative Extension office or soil testing lab for the fee structure, mailing containers, and other information.

·         Using a small shovel or soil probe, sample to a 3-inch depth.

·         Take approximately 10 to 15 samples per lawn and remove thatch and live plant material.

·         Combine the samples to make one composite sample.  Do not mix soils of different texture and color, from areas differing sharply in elevation, or from disturbed sites and undisturbed sites.

·         Air dry the sample before sending.

The Soil Test Report
After processing your soil sample, the soil test lab will send you a soil test report.  The following are usually included in the report:

Soil pH - A soil pH indicates whether the soil is acidic, alkaline, or neutral.  The concentration of soil nutrients will vary depending on the soil pH.  A soil pH below 6.0 indicates an acidic soil and a lime application may be recommended.  DO NOT APPLY LIME UNLESS IT IS RECOMMENDED.  Most Indiana soils under turfgrass do not need liming.

If the soil pH ranges from 6.0 to 7.5, it is unnecessary to adjust the pH.  This is the optimum pH range for turfgrass growth.  For a pH above 7.5 (rarely a problem in this area), there is no practical or economically feasible soil amendment for a lawn.  To compensate for a high pH, increase the annual nitrogen, phosphorus, and potassium applications by 25 percent.     

Phosphorus (P) - The soil test results represent the amount of phosphorus available to the plants from the soil.  Phosphorus deficiencies are rarely observed in established turf in Indiana, except on soils with very high pH.  When establishing or renovating an area, a phosphorus application will help establish seedlings.  A fertilizer high in phosphorus (also called a "starter fertilizer") should be used for this application and should be applied at 1.5 pounds P₂O₅ /1000 ft².

Potassium (K) - The soil test results represent the amount of potassium that is available to the turfgrass plant. Potassium deficiencies are rare in turf in Indiana soils except possibly on coarse-textured, sandy soils. Muriate of potash (0-0-60) can be used to increase soil potassium levels.  Muriate of potash can burn leaf blades, so apply in cool, dry weather and water the area soon after application. 

Cation Exchange Capacity (CEC) - This number represents a measure of your soil's capacity to hold nutrients; the higher the CEC, the more fertile the soil.  It is used by the soil test laboratories in making certain nutrient recommendations for your lawn.  The cation exchange number of an established lawn will not change significantly with time.  In addition, it cannot be adjusted by adding fertilizer or chemicals.

Nitrogen - There is no reliable soil test for nitrogen.  Therefore, other factors should be considered in planning a nitrogen program.  The nitrogen program is the key to a successful turfgrass fertility program.  For more information on nitrogen applications, see Purdue Extension Publication AY-22, Fertilizing Established Lawns.