Selecting an Analytical Laboratory

Introduction 

Soil and manure testing are the foundation of an economically and environmentally sound crop management program. Plant tissue analysis can be a useful method to assess crop nutrient status. Irrigation water testing can help ensure an understanding of the quality of water being applied and allow for nitrogen crediting in some cases. In addition, rural homeowners should periodically test their well water to ensure it is safe for drinking. Testing can help homeowners understand the needs of their lawns and gardens.

There are many qualified laboratories in Colorado and around the region that provide these services. There also are commercially available quick test kits that are less accurate but can be used for testing both soil and water. Without an analysis, you may be buying unnecessary fertilizer or applying too much manure to your fields. Neither practice is sound. In some cases, a $35 soil analysis can save a crop producer thousands of dollars in unnecessary fertilizer costs.

Soil Testing

Yearly sampling of each crop field is recommended to make accurate nutrient management recommendations. Routine soil sampling also provides valuable information about soil salinity, pH, organic matter content, micronutrients and other key soil factors. Obtaining a representative sample is the key to getting accurate results. For proper sampling steps, contact the analytical laboratory that will analyze your samples.

To get a representative sample, use clean tools to collect soil cores from a variety of locations in the field. Combine 20 to 30 individual samples and mix thoroughly before transferring the soil to the sample bag. Avoid (or sample separately) any unusual areas that may impact your results. Break large fields into smaller sampling units based on the planned crop, as well as yield and fertilizer histories. Typically, soil is collected from the top 8 to 12 inches for routine fertility analysis and application recommendations. Separate deep subsoil samples for nitrate analysis are suggested to determine accurate N recommendations for irrigated crops, such as corn, sugar beets, wheat or other plants with deep root systems.

Lawns and gardens also can be improved by soil analysis. Usually about a dozen soil cores to a depth of 4 to 6 inches and then mixed together are adequate for a typical urban lawn or garden sample.

Soils also can be analyzed for less common elements such as selenium or lead, as well as for organic compounds such as pesticides or hydrocarbons. Pesticide tests are expensive and not routinely recommended unless serious contamination problems are suspected. Check with your analytical laboratory concerning the submission of samples for pesticide testing. Sampling for organic compounds often requires special handling. Air dry soil samples as soon as possible by spreading them over a clean paper grocery sack (for boron analysis use plastic sheets) to ensure they are completely dry prior to mailing to the laboratory. Be sure to keep all samples cool until they can be air dried. For best results, deliver samples to the laboratory as soon as possible after drying. The chemical composition of samples kept in warm, moist conditions may change substantially within just a few days and significantly alter test results and subsequent fertilizer recommendations.

Water Testing

Public water supplies have strict federal and state regulations governing water quality and testing. However, if you have a private water system, it is your responsibility to make sure your family’s water is safe. Contaminated water may taste, look or smell the same as safe drinking water. Laboratory analysis is the only reliable method to determine the quality of drinking water.

If you are buying a new property or if you cannot remember when your well was last tested, have your water analyzed by a reputable laboratory for bacteria, nitrate, sulfate, chloride, pH, total dissolved solids (TDS), hardness and conductivity to get baseline information on your well. Annual water testing is suggested to help monitor the quality of your private water supply. If you see a decline in quality, more thorough investigation is warranted. These records will provide valuable information on the history of your well if your water is ever contaminated.

Bacterial analysis is strongly recommended for all private water supplies, especially for a well close to septic systems or animal confinement facilities. Wells can be impacted by factors beyond the wellhead and any obvious sources of contamination. Tests for pesticides and other organic contaminants are expensive and usually not recommended unless you have reason to suspect contamination. Testing for radon is recommended when indoor air radon levels are high and the water source is groundwater.

Follow your laboratory’s sampling procedure when collecting water samples. Many laboratories provide clean containers with detailed instructions on sample collection. If one is not provided, use a clean plastic container. Wash your hands prior to sampling and do not touch the inside of the container or lid. Rinse it three times with the well water before you collect the actual sample. Let the water flow for about five minutes before sampling. Do not draw from an aerated faucet or a swing arm faucet (the aerator can be removed prior to sampling). For best results, keep the sample refrigerated and return it to your lab within their recommended time frame. If shipping refrigerated samples, be careful to ship them so they will arrive during business hours. If samples arrive after business hours or on the weekend, they may not be analyzed within the laboratory’s required time frame.

Manure Testing

Analyze manure for nitrogen, phosphorus, potassium and salt content. Obtaining a representative manure sample can be challenging. For proper manure sampling, you need a clean bucket and sample jar. If you spread manure daily, take many small samples over a representative period. For periodic spreading from a manure pack or pile, use a clean shovel or fork to collect samples from a variety of locations in the pack or pile. Be sure to collect both manure and bedding if they are applied together. Agitate liquid manure handling systems before sampling and collect several separate samples.

Combine the individual spot samples from a particular lot or lagoon in the bucket and mix thoroughly before filling the sample jar. Keep the sample refrigerated and deliver it to the laboratory within 24 hours if possible. If a food refrigerator is used to store it, wrap the sample in several layers of clean plastic and put it in a tightly-sealed plastic container.

Collect the samples in advance of your spreading date so you have time to obtain test results and calculate the correct application rate for the crop to be grown. If this isn’t possible, it is still helpful to analyze a representative sample so you know how much to credit in the future. An accurate manure test is an excellent investment of time and money. It can help you save fertilizer costs, ensure adequate nutrients for your crops and help avoid potential water contamination issues.

Plant Analysis

Plant analysis during the growing season can help assess nutrient sufficiency in a growing plant. While some nutrient deficiencies may be apparent, excess nutrient levels can be determined only by plant tissue analysis. Plant analysis allows you to adjust for plant nutrient needs during the growing season. Plant analysis, when properly used, offers producers insurance that careful nutrient management will not negatively affect the bottom line. For more information, see CSU’s Plant Analysis Fact Sheet.

Choosing a Laboratory

Individual laboratories vary in analytical philosophy, services offered, cost and the time required for analytical results. The following list of laboratories is not all-inclusive, and the list of services may change over time. To select a lab, consider convenience, services offered and quality. To ensure the lab can meet your needs always reach out to them directly prior to submitting your samples.

There is a North American Laboratory Proficiency Program administered by the Soil Science Society of America (naptprogram.org). This program provides a manual with detailed descriptions of recommended analytical methods and also runs a Quality Assurance/Quality Control (QA/QC) program. Participating labs are sent samples to analyze throughout the year and their results are compared to other laboratories. These comparisons results are sent back to the labs to help them improve techniques and methods. While not required, participation in this program generally indicates a laboratory has high standards for precision and accuracy.

Laboratories should have their own QA/QC program in-house to catch human and instrument errors that may occur. By running duplicate samples and comparing results, or by periodically analyzing standards (samples with known values) during sample runs, a lab can determine if its results are reproducible, precise and accurate.

Fertilizer recommendations are based on soil test results. However, there are differing nutrient management philosophies that will impact recommendations. Be sure your laboratory’s philosophy is consistent with your objectives. One approach is to build up soil fertility levels, another approach is to replace the amount of nutrients taken up by a crop, and a third approach is to base fertilizer recommendations on crop requirements to maximize yield. The first two approaches result in higher fertilizer recommendations that can lead to a buildup of nitrogen and phosphorus in the soil and potential pollution of water sources. Applying only what the current crop requires is a best management practice for both productivity and environmental protection.

Questions to Ask

Call the laboratory manager prior to sample collection to determine the laboratory’s suitability and to get more detailed information. You may want to ask some of the following questions:

1. What analyses does your laboratory offer?
2. What do they cost?
3. How long will it take to get my results?
4. Do you participate in the North American Laboratory Proficiency Program or other accreditation program? If so, how has your performance been?
5. Are your analytical methods EPA-approved or described in the North American Laboratory Proficiency Program lab manual?
6. Is the lab associated with a co-op or fertilizer company?
7. What is your lab history? How long have you been running analyses similar to what I need?
8. What is your philosophy in making fertilizer recommendations? Are your recommendations research-based?

Recordkeeping and Interpretation

Keep a record of your lab results as a reference for future testing. If you need help interpreting the results of your sample, the lab manager where the sample was analyzed or your CSU Extension County Office can assist you. Different labs may vary in analytical tests used, reported concentration values, and in actual fertilizer recommendations.

Commonly used laboratories