Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityDecember, 1998
OSU REAL Laboratory Closes
Keywords: soil/media testing, soils, water testing, fertility, nursery, landscape, micronutrients, container media
A fter many years of serving Ohioās agricultural industry, the Research Extension Analytical Laboratory (REAL) of OSU is closing at the end of 1998. The REAL lab has provided testing services for soil, media, plant tissue, feed, manure, and compost. The most common tests used by the nursery industry included the soil, soilless mix, plant tissue, and water analyses. Growers and landscapers who find themselves switching from one testing laboratory to another can expect to see differences in the way results are expressed (and interpreted) and perhaps in the types of tests that are used. Itās possible that test results from a new lab may require an entirely different set of interpretive guidelines. A testing lab should provide appropriate guidelines with their test results, although the guidelines may not be specifically geared to nursery crops. Your OSU Extension agent also can help interpret results if you switch to a new lab. This article is a guide to the types of changes that may be encountered when switching labs.
The mineral soil test. The standard soil test provided by the REAL laboratory included a lime recommendation (if needed), available phosphorus (P), exchangeable calcium (Ca), magnesium (Mg) and potassium (K), base saturation for Ca, Mg, and K, and the cation exchange capacity (CEC). Most labs in the Midwest are probably using the same or similar tests for these values, however, the units in which they express the values may vary. For example, the REAL lab recently switched over to using PPM (parts per million) instead of lb./A (pounds per acre) to express available P and exchangeable Ca, Mg, and K. If you change from the REAL lab to a commercial lab using lb./A, expect to see these soil test values double, since 1 PPM = 2 lb./A. Millequivalents per 100 grams (meq/100g) is yet another unit sometimes used to express exchangeable Ca, Mg, and K. Somewhat more complex computations are required to convert meq/100g to lb./A.
Soil soluble salts (EC) is a special soil test that is useful if over-fertilization or deicing salt problems are suspected. Itās particularly confusing to compare this test between labs because EC may be expressed several different ways. The REAL lab used Mhos x 10-5/cm (for the soil test, but not for the soilless test). Most labs use mmhos/cm. The difference is a factor of 100. For example, 100 Mhos x 10-5/cm = 1 mmhos/cm.
The soilless mix test. The soilless test is the appropriate choice for most container media used today, even if they contain a small percentage of soil. Soilless tests provide pH, nitrate-N, soluble salts (EC), P, K, Ca, Mg, and some microelements, typically iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn). Labs may also provide ammonium-N, chloride, fluoride, sulfate-S, boron, molybdenum, and sodium as part of a standard test package. Most labs are using the saturated medium extract procedure (SME) although some may be using a 1:2 soil-water dilution procedure. The same sample extracted by the SME method can be expected to have nutrient values approximately double those from the 1:2 dilution method, because less diluent (water) is used in the SME. With one exception, results from different labs that use the same dilution procedure (either SME or 1:2) should be very similar. Micronutrients can vary however, because some labs (including the REAL lab) use a chelating agent (DTPA) when extracting media for micronutrients. Use of the chelating agent results in higher micronutrient test values than the water-only extraction procedure, and different interpretive guidelines should be used.
Plant tissue tests. A plant tissue test (most commonly leaves) reflects the elemental content of the tissue. The whole tissue, not an extract, is tested; thus results will not vary from lab because of different extraction procedures. Labs may use different types of equipment to perform the analyses, but the same sample submitted to different labs should nonetheless produce very similar results. Nitrogen content of plant tissue can vary between labs somewhat because of two fundamentally different methods of determination; however even in this case, the difference is not more than a few tenths of a percent. Tissue concentrations of macroelements (N, P, K, Ca, and Mg) are usually expressed as percent by dry weight of tissue, and the microelements (Fe, Cu, Mn, Zn, B, etc.) are expressed in PPM.
Water tests. An irrigation water analysis usually provides all or most of the following: pH, alkalinity, soluble salts, nitrate-N, ammonium-N, P, K, Ca, Mg, Fe, sulfate-S, Mn, Zn, Cu, B, Cl, F. As with plant tissue-testing, results from lab to lab should be similar because no extraction process is used. All elements are expressed in PPM. Alkalinity is the only parameter in a water test that may be expressed differently between laboratories. The REAL lab expressed alkalinity as PPM of calcium carbonate; whereas some labs use PPM bicarbonate. To convert from one to the other: 1 PPM CaCO3 = 1.2 PPM HCO3-.
Testing laboratories. Table 1 contains a list of laboratories that perform one or more types of analytical procedures. This list is offered as a reference to growers and landscapers, but no endorsement of any lab is implied. When choosing a lab, considerations include not only cost, but also turnaround time, lab reputation, and attention to accuracy and precision. Granted, there is no easy way for a prospective client to judge the latter characteristics. But if lab representatives are able to intelligently discuss testing procedures and offer interpretive advice this is a good sign.
Table 1. Regional soil test labs that also may provide media, water and tissue testing.
Lab Location Telephone no.
Agricultural analytical services laboratory (Penn State) State College, PA 814-863-4540
Alloway Testing Mansfield, OH 419-535-1644
A & L Great Lakes Lab Fort Wayne, IN 219-483-4759
Brookside Labs New Knoxville, OH 419-753-2488
CLC Labs Westerville, OH 614-888-1663
Calmar Lab Westerville, OH 614-523-1005
Countrymark/Land OāLake Indianapolis, IN 317-685-3000
Holmes Lab Millersburg, OH 800-344-1101
Na-churs Marion, OH 800-622-4877
Scotts Testing Laboratory* Allentown, PA 800-743-4769
Spectrum analytical Washington Courthouse, OH 800-321-1562
Woodsen-Tenent Dayton, OH 937-222-4179
*Provides media testing, but not soil testing.
