Soil Testing Procedures for Calcareous Soils

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Soil Testing Procedures for Calcareous Soils Well-established soil testing methods on soils containing calcium carbonate or gypsum often underestimate fertilizer and soil amendment requirements. BY BRIAN WHITLARK

magine a scenario where you have been consistently collecting soil data Table 1. Ifor tees, fairways, and greens for Laboratories may offer one or more of the following soil extracting more than fi ve years, using one lab solutions to determine exchangeable cations and estimated CEC. and one procedure. Does this sound Soil Testing Extractant Solution pH Notes familiar to you? If it does, great! Regular Mehlich 1 1.5 Should not be used to determine soil testing is an invaluable tool for cations on calcareous or developing and fi ne-tuning fertilizer gypsiferous soils and soil amendment programs. Receiving accurate and consistent Mehlich 3 2.5 Should not be used to determine values from the laboratory, coupled cations on calcareous or with personal observations, allows for gypsiferous soils intelligent decision-making in the fi eld. Modifi ed Morgan 4.8 Should not be used to determine But what if you were to discover that cations on calcareous or the data for all those years was wrong? gypsiferous soils Would you change to a more accurate Saturated Paste 7.0 Yields nutrients in the soil solution procedure? If you grow turf on calcareous soils (those containing calcium 1:5 soil-water extraction 7.0 Values must be corrected to carbonate) or gypsum, it is possible, correlate with saturated paste and even likely, that you should con- Ammonium Acetate 7.0 Most commonly used extraction sider changing soil testing procedures. method, but should not be used on However, in the absence of free calcareous or gypsiferous soils carbonates or gypsum, a change in Ammonium Chloride 5.5 Not commonly used due to soil testing methods is unneeded. The extra steps that account for the objective of this article is to alert golf dissolution of calcium carbonate course superintendents who manage turf on calcareous or gypsiferous soils Elevated pH >8.0 Most accurate extraction currently (containing gypsum in excess of 2%) Ammonium Acetate used for soils containing calcite or that nutrient data obtained from the gypsum most commonly used and accepted soil testing extractants may result in shaken with the soil, the extractant is IS THERE A PROBLEM WITH misguided fertilizer and soil fi ltered and analyzed for soil nutrient THE EXTRACTANT THAT I AM amendment programs. content. It is important to understand CURRENTLY USING? the nutrients removed from the soil The answer may be yes, especially if WHAT IS A SOIL TESTING represent those nutrients immediately you are growing turf on a calcareous EXTRACTANT? available and those that are slowly or gypsiferous soil. Unfortunately, a Nationwide, soil laboratories that test available for turf use. An entirely differ- “universal” soil testing extractant is golf tees, fairways, and putting greens ent test provides total nutrients in the not currently available, hence a wide use a variety of soil extractants to soil — those that are available and variety of solutions are used, including determine plant-available nutrients those that are unavailable or “structur- acid extractants such as Mehlich I, in the soil. You may wonder what ally bound” in the soil. A third test is Mehlich 3, and the Modifi ed Morgan, exactly a soil testing extractant is. An the water-based extraction (saturated a neutral pH ammonium acetate extractant is a solution of water and paste test), which measures only what extractant (pH 7.0), and the elevated various chemicals that, when mixed is in the soil-water solution or immedi- pH ammonium acetate solution (>pH with soil, extract or remove nutrients ately soluble at the time of testing and 8.0) (Table 1). The problem is this: from the soil that are: 1) contained in grossly underestimates the nutrient when testing a soil that contains cal- the soil solution, 2) easily dissolved in supplying power of the soil. These cium carbonate, magnesium carbonate, water, and 3) held on soil exchange three extracting methods are often or gypsum, the acid and neutral pH sites and available for plant use. Once confused. extractants overestimate calcium (Ca)

Green Section Record Vol. 49 (9) TGIF Record Number 176852 March 4, 2011 Page 1 HOW WILL THE WRONG EXTRACTANT AFFECT MY FERTILIZER PROGRAM? When testing a calcareous soil, acid and neutral extractants will overestimate ECEC, exchangeable Ca, and related base saturation percentage and cation ratios. Although research does not support the use of cation ratios and percentages as a basis to develop fertilizer programs, those turf managers who still use this method will ﬁ nd the data they have been using is incorrect if their soils contain calcium carbonate and the soil testing extractant is acidic or has a neutral pH.

HOW WILL THE WRONG EXTRACTANT AFFECT MY SODIUM REDUCTION PROGRAM? Mike Rothenberg, a soil consultant for Brookside Laboratories, encourages When acid is placed on a soil containing appreciable calcium carbonate, the soil turf managers in the Southwest to use fi zzes in the form of carbon dioxide gas bubbles. the elevated pH ammonium acetate extractant. Mr. Rothenberg stresses the importance of testing the soil to and to a lesser extent magnesium is quite accurate and results in a value confi rm the presence of calcite prior to (Mg). For example, when the pH- similar to the actual CEC. The actual recommending a change in soil testing neutral ammonium acetate extractant CEC is measured via a complex, time- procedure. Over the last few years, Mr. is used on a calcareous soil, it may consuming procedure and is typically Rothenberg noticed that when super- overestimate Ca by as much as 60% only performed upon request. Testing intendents changed to the correct (3). In another example, the pH 7.0 a calcareous soil with a neutral or acid extractant, they were always surprised ammonium acetate procedure may extractant will overestimate Ca and Mg, to see the Ca levels decreased and the yield up to 40% more calcium than is and when the cations are summed, the sodium percentage increased. Many actually available for plant use and estimated CEC is much higher than realize they need to modify their Na exchange for sodium (Na) in the soil the actual CEC. It is important to note reduction program to address the (2). Overestimating Ca levels in the that such an error does not occur in correct values. Let’s take a look at a soil not only affects Ca, but will cause the absence of Ca or Mg carbonates few examples where turf managers in inaccurate estimates of CEC, base or gypsum. Largely dependent on the Arizona have realized the benefi ts of saturation levels, and cation ratios, and calcium carbonate levels in the soil, accurate soil test data. will underestimate the exchangeable the ECEC may be overestimated by sodium percentage (ESP). a substantial margin. The more the calcium carbonate, the greater the HOW WILL THE WRONG difference will be. EXTRACTANT AFFECT THE It is important to know whether the SOIL CATION EXCHANGE soil has a high or low CEC when deter- CAPACITY? mining fertilizer frequency and rates. A Overestimating Ca and Mg will result low-CEC soil will require more frequent, in erroneously high estimated CEC light fertilizer applications to sustain values (ECEC). You may be curious healthy turf and to avoid unnecessary what “estimated CEC” means. Soil nutrient losses due to over-application testing laboratories often calculate and subsequent leaching. The CEC the CEC by summing the four basic is also commonly used to determine Different soil testing methods are cations: Ca, Mg, K, and Na. Such a gypsum, sulfur, and lime requirements used to determine the total nutrients in calculation assumes the cations and to calculate amendments to the soil, the available nutrients, and occupy 100% of the soil exchange remediate sodium affected (sodic) those in the soil solution. These three sites. In alkaline soils, this assumption soils. extracting methods are often confused.

Green Section Record Vol. 49 (9) March 4, 2011 Page 2 Calcium extracted with ammonium acetate pH 7.0 and 8.5 Exchangeable Sodium Percentage using ammonium acetate extractant at pH 7.0 and 8.5 6000 0.300

ESP (pH 7.0) ESP (pH 8.5) 5000 Avg. 0.238 4,596 ppm Avg. 18% pH 8.5

4000 0.175

Ca pH 7.0 Ca pH 8.5 Avg. 13% pH 7.0 Calcium in parts per million Text Avg. Exchangeable Sodium Percentage (ESP) 3000 2,845 0.113 ppm

2000 0.050 123456789101112131415161718192021222324252627282930 123456789101112131415161718192021222324252627282930

Figure 1. Calcium values extracted with ammonium acetate Figure 2. Exchangeable sodium percentage computed using at pH 7.0 (red line) and pH 8.5 (green line) from 30 soil exchangeable cation values from 30 different soil samples samples collected from a calcareous soil fairway in collected from a calcareous soil fairway in Goodyear, Ariz., Goodyear, Ariz. with ammonium acetate at pH 7.0 (red line) and at pH 8.5 (green line).

GOODYEAR, ARIZ., fact, the turf was so thin, the members pore space, yet not so much that any GOLF COURSE FAIRWAY were not allowed to drive on the fair- water rests on top of the soil. The In a study completed in 2008 (3), 30 way. Soil testing using the Mehlich 3 soil-water paste is poured into a funnel soil samples were collected from a extractant revealed Ca levels equaled lined with fi lter paper and placed over calcareous soil fairway in Goodyear, about 7,400 ppm, Na levels at 1,700 a vacuum to suck the soil solution from Ariz. The soils were analyzed with ppm, and an ESP of 14%. Recommen- the mixture. The fi ltered solution is ammonium acetate at pH 7.0 and at dations called for an annual gypsum analyzed for nutrient content. pH 8.5. Averaged over the 30 soils, the program at about 3,100 lbs/acre, in The saturated paste test shows the extractant with the neutral pH overesti- addition to frequent aeration. However, nutrients immediately available during mated Ca by 1,800 ppm (3,600 lbs/ once the correct soil testing procedure one irrigation event, but keep in mind acre) (Figure 1), and Mg by 120 ppm was used, the data revealed that Na that the values will be different during (240 lbs/acre). Moreover, the average levels remained unchanged, but Ca the next irrigation cycle or rainfall event. Na percentage (ESP) was calculated decreased to only 4,900 ppm and The water-based test does not include at 13% with the neutral extractant and consequently, the ESP increased to the nutrients held on soil exchange more than 18% for the elevated pH 21%. As a result, gypsum applications sites or those that are moderately solution (Figure 2). These soils are were increased to 6,700 lbs/acre/year soluble, which are available for plant classifi ed as sodic, or sodium affected and the superintendent employed a use. Unfortunately, some labs still soils, but are categorized incorrectly more aggressive aeration and leaching report that the nutrients extracted with when using the wrong extractant. How strategy. After one year, Ca levels solutions such as ammonium acetate does this affect the gypsum require- soared to nearly 10,000 ppm (as are not available for plant use. As a ment in this example? Based on the pH measured with the correct extraction), result, some turf managers will use 7.0 solution, the gypsum requirement Na dropped to about 1,000 ppm, and the saturated paste test to determine averages 3,000 lbs/acre to reduce the the ESP decreased from 21% to only fertilizer requirements, but such an ESP to 8%, but increases to nearly 7.9%. More importantly, members can approach will lead to unnecessary 4,500 lbs/acre when using the correct now enjoy the turf conditions on this nutrient applications. extractant. This scenario is not uncom- fairway all year long. Nutrient levels found in saturated mon in the Southwest, where native paste tests will be considerably lower soils and sand rootzones are often WHY NOT USE THE WATER- than other extraction methods and calcareous and Na is high from BASED METHOD INSTEAD? should not be used to base fertilizer irrigation inputs. The water-based extractant, also programs. Calcium and potassium are known as the saturated paste test, good examples of nutrients that are SUN LAKES, ARIZ., offers a snapshot in time of the nutrients sometimes applied as a result of low GOLF COURSE FAIRWAY in the soil-water solution and those that values reported on a water-based In a second example, a superintendent are immediately soluble. A saturated extraction. It is not uncommon for Ca in Sun Lakes, Ariz., struggled with turf paste is made by mixing the soil with and K levels from a water-based test to on his 12th fairway for several years. In enough water to completely fi ll the register only 4-5% of those found on

Green Section Record Vol. 49 (9) March 4, 2011 Page 3 other extractions. For example, a recently collected soil test from a golf course green in Arizona revealed Ca and K values of 3,000 and 230 ppm, respectively, with an ammonium acetate extraction (pH 8.5). The water- based extraction yielded only 67 ppm Ca and 11 ppm K. Tissue tests con- ﬁ rmed both Ca and K were sufﬁ cient in the plant, even though nutrient levels in solution were low, as was expected. If the water-based test was the only method used, one might fertilize heavily with Ca and K. It is known that excessive Ca additions typically reduce tissue K and Mg, and con- versely, over-applying K often results in reduced plant tissue Ca and Mg levels. The water-based extraction should be used to determine total soluble salts, soil pH, and the Sodium Adsorption Ratio (SAR). Keep in mind that the SAR is a useful tool to predict the Na Using the wrong extracting solution on soils that contain calcite or gypsum can hazard of the soil, but should not be underestimate fertilizer and soil amendment requirements. confused with the percent Na that is often reported on saturated paste wide variety of soil types, but as of answered “yes,” and you may consider tests. right now, the only commercially avail- contacting one of the following able extractant suitable for alkaline, laboratories that offer the elevated pH I GROW TURF ON AN calcareous soils is the elevated pH ammonium acetate procedure: ALKALINE, CALCAREOUS ammonium acetate extractant. Early SOIL: WHICH LAB in this article the question was raised Kuo Testing Labs, Inc. SHOULD I CHOOSE? whether you would change to a more Othello, WA Research is needed to develop new accurate soil testing method. If you http://kuotesting.com extractants that are suitable for a have made it this far, you likely MotZZ Laboratory, Inc. Tempe, AZ http://www.motzzlaboratory.com

Brookside Laboratories, Inc. New Knoxville, OH http://www.blinc.com

Best-Test Analytical Services Moses Lake, WA http://www.besttestlabs.com

Soiltest Farm Consultants, Inc. Elevated pH extraction available upon request Moses Lake, WA http://www.soiltestlab.com

Note: The list of laboratories offered here is not inclusive, and you might want to contact the laboratory you are currently A “universal” extracting solution is not currently available, so turf managers must working with regard to the elevated pH choose the right extractant for the soil type at their courses. ammonium acetate method.

Green Section Record Vol. 49 (9) March 4, 2011 Page 4 In the desert southwest, where irrigation water often contains high sodium levels, it is imperative that agronomic programs are based on accurate soil data.

WHY CAN’T WE FIND A six different soil testing extractants. cations in calcareous soils. Commun. Soil Sci. Plant Anal. SUITABLE EXTRACTANT The SrCl2 method and a new potential 29:1785-1791. extractant called silver-thiourea were FOR ALL SOILS? 2. St. John, R. A., and Christians, N. E. evaluated, in addition to the commonly Research is ongoing to fi nd a soil 2010. Special approaches are needed used extracting solutions. The soils testing extractant suitable for a wide when testing calcareous sands. were divided into groups that contain a variety of soil types with diverse pH, Online. Applied Turfgrass Science range of CEC values (0-5, 5-10, 10-20, CEC, and calcium carbonate levels. doi:10.1094/ATS-2010-0831-01-RS. One such extractant that shows poten- 20-30 and >30 meq/100g soil). The tial is a dilute solution of strontium soils represented a diverse cross sec- 3. Whitlark, B., and Umeda, K. 2008. tion of soil texture (clay content 5-60%, Unpublished Data. chloride (SrCl2). Dr. Micah Woods’ research compared SrCl to commonly sand content 11-91%) and calcium 2 4. Woods, M.S. 2006. Nonacid Cation levels (21-9760 ppm). The data from used extractants to determine if the Bioavailability in Sand Rootzones. PhD SrCl method may be used to measure this evaluation may be available about 2 dissertation. Cornell University. the basic cations and ECEC (4). His the time this article is published. Ideally, labs may one day use a 5. Woods, M. S., Ketterings, Q. M., research revealed the SrCl2 method works very well regardless of calcium single extractant to easily and effi ciently and Rossi, F. S. 2005. Measuring the carbonate content and soil pH; how- assess soil nutrients regardless of Effects of Potassium Application on ever, it is generally limited to soils with soil pH, CEC and calcium carbonate Calcium Magnesium Availability in a fairly low CEC values (< 6 meq/100g content. If and when such a solution is Calcareous Sand. International soil). Dr. Ketterings and other scientists available, it will simplify soil testing Turfgrass Society Research Journal. at Cornell University are currently interpretations — a welcome notion in Volume 10. the complex world of soil testing. studying the ability of the SrCl2 extraction to accurately assess soil cations BRIAN WHITLARK is an agronomist on higher CEC soils. REFERENCES in the Southwest Region of the USGA In another study, Dr. Bob Miller 1. Normandin, V., Kotuby-Amacher, J., Green Section. He joined the staff in and Brian Whitlark sent 18 soils to fi ve and Miller, R. O. 1998. Modifi cations of 2008 and visits courses in Arizona, different laboratories across the United the ammonium acetate extractant for California, Nevada, and portions of States. The soils were analyzed using the determination of exchangeable Mexico.

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