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Don't Guess....Soil Test

Scott Guiser
Penn State Cooperative Extension
Doylestown, PA

July-August, 2002

Don’t guess…. soil test. That’s the motto of horticulturists and good grounds managers. Soil testing is a service provided by most “Land Grant“ universities (Penn State, Florida State, Purdue, Rutgers, Cornell, etc). Private labs do soil testing, too.

Soil tests measure the levels of several essential plant nutrients and soil pH. This information is used to make recommendations for proper amounts of fertilizer and lime. Turfgrass, woody landscape plants, bulbs and annual flowers all have specific nutritional requirements. Soil pH and nutrient levels vary greatly from site to site. So, guesses about nutritional needs often miss the mark. A small investment in a soil test will insure that you are applying the proper amounts of fertilizer. Sometimes, soil tests save you money by revealing that adequate quantities of soil nutrients are already present.

Soil testing is especially important when new, perennial plantings are being planned. You’ve got to incorporate lime (to raise pH) or an acidifier such as aluminum sulfate or sulfur (to lower pH). Also, some elements such as phosphorus, calcium and magnesium are not mobile in the soil and should be incorporated to the rooting depth of landscape plants for best effect. Obviously this must be done prior to planting. Consider a new athletic field. A simple soil test prior to finishing grading will allow you to “till in” the necessary nutrients and amendments. Now imagine this…. six months after establishment the seeding is struggling. You discover very low phosphorus levels and a pH of 4.5. Lime and phosphorus can no longer be incorporated and their movement into soil and availability to the plant roots are severely restricted. You’re stuck in a bad situation that could have been avoided. The moral to this story….. keep soil testing in mind as you plan new plantings.

Here’s the procedure for obtaining a good sample and interpreting the results:

(1) Purchase a soil test mailing kit. They are available from most “Land Grant” universities and private labs for a modest fee. University testing services also will make a fertilizer recommendation.

(2) Beg, borrow, or buy a soil sampler. This is a piece of tubing or cork-screw device with a handle that you insert into soil to remove a profile of the soil. Where soil is tilled a trowel or shovel will work. A soil sampler works best, especially in existing sod.

(3) Define the area to be tested. It may be a flower bed, the university president’s lawn, or the varsity football field. In any event, criss-cross your way throughout the area and sample 12-15 locations. Put these sub-samples together into a clean container. Paper lunch bags work well. Sample three inches deep for turf and eight to 12 inches deep for woody plants and other ornamentals. Avoid sampling odd spots in any site. Throw out stones, sod, mulch and thatch. You will collect more soil than is needed for testing. However, it is essential that you collect a representative sample for the site. A lousy sample will lead to lousy fertility recommendations.

(4) If more than one site is being tested, be sure to code them so that you know what’s what when the results come in. The soil test information sheet has a space for you to give the sample a name.

(5) Complete the questionnaire that comes with the soil test kit. You must indicate what “crop” you are growing such as, “athletic field - to plant” or “lawn maintenance.” The directions are self-explanatory. Follow them carefully. For instance, it is very important that you indicate whether the site being sampled is already planted or is to be planted. This affects the recommendation.

(6) Mix and add soil to the soil pouch on the mailing kit after it has air dried over night. Then add postage to the pre-addressed mailing kit and send it off.

(7) Results will come back from the lab in about two weeks. In many states, university labs also send a copy to the local cooperative extension office. If you have questions about interpreting the results, call your county extension agent. Fertilizer reps and sales people can also assist.

Don’t guess ….soil test. It is an inexpensive investment in plant health.