SAMPLING

C. Owen Plank and R.N. Carrow¹

Sampling is one of the most critical phases of a plant analysis program. Most laboratories provide plant analysis sampling kits which contain detailed sampling instructions along with a history form and envelope for submitting samples to the laboratory. The sampling instructions should be followed carefully. A sample taken improperly provides little or no information about the problem at hand.

When sampling turf from areas other than golf greens, hand clippings are preferred to mower clippings. Make sure that the instruments (clippers or scissors) used to collect the clippings are clean and free of any rust. Collect  2 to 3 handfuls of tissue, place in brown paper bag or plastic container, and save for additional preparation, washing and drying, prior to shipment or on-site analyses.

Generally, the surfaces of golf greens are relative free of foreign debris. However, at certain times of the year leaf fall from adjacent trees may result in leaves on the surface of the greens. These should be removed with a backpack blower or other suitable device prior to sampling.

Mower clippings from golf greens can be used for turfgrass analysis using the normal mowing height at the site. Clean mower baskets are acceptable for catching the clippings. However, care should be taken to wash off any soil that may contaminate the clippings. After the area has been mowed, randomly remove 3 to 4 handfuls of clippings from the basket of walking mowers or 2 to 3 handfuls from each basket of Triplex mowers and place in a brown paper bag or plastic bucket. (If clippings are transferred to a bucket, be sure to use plastic as metal containers may result in contamination of the sample.) Mix the sample thoroughly and withdraw three handfuls and place in a labeled container (plastic or double-lined paper bag). Save the sample for additional preparation, washing and drying, prior to shipment or on-site analyses.

Do not sample within a week after fertilizer or other chemicals have been applied to turf. These materials can contaminate the sample and invalidate analytical results. Other common contaminates on turfgrass that can affect analytical results are sand and soil particles. Particulate matter on clippings from golf greens have been shown to adversely affect both the consistency and reliability of analytical results for unwashed samples (McCrimmon, 1994). Failure to remove sand from samples using proper washing techniques generally, with the exceptions of iron and aluminum, results in lower nutrient concentrations as compared to washed samples. When samples are contaminated with sand or soil particles, the analytical results for both iron and aluminum are high. To minimize the amount of sand in samples from golf greens, do not take samples immediately after topdressing. Wait until the sand is watered in and settled. This may require several days. Also, avoid taking samples on days the grooming heads are attached to the mowers. The grooming heads result in increased sand and other foreign materials in the sample and prolongs the washing procedure.

Do not include diseased or dead plant material in a sample. Also, avoid sampling plants which have been damaged by insects and nematodes, stressed extensively by cold, heat, moisture deficiencies, or by excess moisture.

The frequency of sampling depends upon whether the results will be used for diagnostic or monitoring purposes.

Diagnostic Sampling

The diagnostic role has been the traditional use of plant analysis for turfgrass situations. It is used to confirm a suspected nutrient deficiency or toxicity prior to applying corrective measures. Samples are obtained from (a) an area exhibiting the deficiency symptoms; (Note: Samples from turf where the symptoms are just appearing are much better than from areas with severe symptoms; areas with dead turf should be avoided); and (b) an adjacent normal-appearing area.

Monitoring Sampling

Use of plant tissue analysis to monitor the nutrient status during the growing season has been a common practice for irrigated-annual, orchard and greenhouse crops. However, interest has increased over the past 10 to 15 years for monitoring turfgrass sites, especially greens. On USGA spec greens, rainfall and/or frequent irrigation can leach nutrients such as nitrogen, sulfur, and to a lesser extent potassium from the root zone. By monitoring the greens regularly turf managers can correct nutrient problems before deficiencies occur. For monitoring, tissue samples are collected as described previously except samples should be taken from the same location on a periodic basis. For example, if clippings are collected from the entire green, use clippings from the entire green throughout the monitoring period. Don’t collect clippings from the front of the green one time and from the back the next time. . Frequency of sampling normally varies from monthly to biweekly, depending upon local situations.

Sample Preparation

Regardless of precautions taken in sampling, turfgrass clippings often contain sufficient amounts of chemicals, sand, or soil on the leaves to influence analytical results. In order to remove the contaminants the samples must be washed or rinsed. For clippings that are relatively free of contaminants place the sample in a plastic or metal sieve and rinse briskly with running tap water. Remove the sample and place on a paper towel and blot. Then transfer the sample to a dry paper towel, place in an area free of chemicals and dust, and allow to air dry.

Greens that have been recently topdressed usually contain considerable amounts of sand or soil particles and merely rinsing the sample in a sieve is not effective in removing these particles. They can be removed more effectively by placing the sample into a wide mouth-container about ¾ filled with tap or distilled water. Swirl the sample gently with a plastic stirring rod or fingers; pause for about 30 seconds to allow the sand to settle to the bottom of the container; quickly remove the sample and place in a sieve or screen and allow to drain; remove and place on a paper towel and blot to remove excess moisture. Then transfer the sample to a dry paper towel, place in an area free of chemicals and dust, and allow to air dry. Discard the wash water, rinse the vessel, fill ¾ full with tap or distilled water and proceed with the next sample.

Samples taken from areas where chemicals have recently been applied should be washed using a weak soap solution (0.1 - 0.3%) rather than tap or distilled water alone (Plank, 1989; Campbell and Plank, 1992). After the sample has been washed place it into a metal or plastic sieve and rinse with distilled, deionized, or tap water. If iron, manganese or zinc deficiency is suspected, distilled or deionized water should be used as the rinse.

Washing should only be performed on fresh samples and never on dry samples. Washing dry or partially-dried samples can result in significant leaching of the soluble elements from the tissue. The washing and rinsing procedures should be done rapidly. Do not prolong the washing procedure or allow the sample to “stand” in either the wash or rinse baths. Allowing samples to remain in the wash or rinse water too long results in low analytical results for elements such as nitrogen and potassium.

After the samples have been air dried remove about 2 handfuls of the sample and place into a plant analysis kit for shipment to the laboratory. If plant analysis kits are not available, paper bags are preferred for shipping rather than polyethylene or plastic, which can speed decomposition. Where analysis equipment, such as NIRS, is available on the site, drying should be according to the manufacturer’s protocol.

Information requested on the history form, which is included with each plant analysis kit, should be as complete as possible. This information is very important to the individual interpreting the results and making the recommendation. The better the information, the more complete the recommendation. Also, when doing diagnostic work don't forget to take soil samples from the same area that the plant samples are taken.

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¹Associate Professor and Professor, The University of Georgia, Crop & Soil Science Department, Athens, GA 30602-7272 and Griffin, GA 30223-1797, respectively.

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