By Susan Shaner
Soil lab selection: How does anyone choose the right laboratory? Aren’t they all the same? Should you send a sample to several different labs and average the results? How do you get the samples to a lab and what is the turnaround time? Some homework needs to be done here.
These are all questions that I hear on almost a daily basis. All labs are not the same. This does not mean that one laboratory is better than another. They all provide a different “menu” of services. It is important to find a lab that provides all of the services that you require. Are you just looking for a soil analysis, or do you also need an irrigation water test or tissue analysis?
Laboratories can also choose from a number of methods or “recipes” to obtain results. Which method would be best for your soil type or crop? “Presentation” of results can also vary greatly from one laboratory to another. It is important that you can read the report and make use of the information it provides. These are all questions that you should consider before choosing a laboratory.
Menu of Services
Packages with various soil parameters are usually available, plus some a la carte choices. This will vary greatly from one laboratory to another. I think we all agree now that there is a lot more to soil than pH. Therefore, look at what is included in the soil package you are requesting.
Important parameters include pH, organic matter, exchange capacity and base saturation. Also important are the major elements calcium, magnesium, potassium, sodium and phosphorus.
Important minor elements include sulfur, boron, iron, manganese, copper, zinc and aluminum. A complete soil analysis including all of these parameters may cost a little more. More information will provide better insight into your fertility situation. If you base your decision on cost alone, you will probably get what you pay for. An inexpensive analysis may only include pH, phosphorus and potassium.
Methodology is the most confusing area when comparing laboratories. There are several different methods for almost every parameter on a soil analysis. Laboratories choose methods that are best suited for the geographical area that they service. Most labs will offer different methods upon request to accommodate most customers; you will have to know what to request first.
Sending the same sample to several labs for comparison will be quite confusing unless you do your homework to determine what methods are used. I have talked with several customers after they have submitted the same sample to different labs without understanding the differences.
They have been very unhappy and disappointed with the outcome. Let’s look at a good example of different methods — for example, phosphorus. There are nine phosphorus test methods that I am aware of. All of these methods were run on a specific soil sample and produced results anywhere from 10.5 to 656 ppm. If you know how to interpret the results for each of these tests, you should come up with the same recommendation. If you do not have the correct threshold levels for the method provided, you could make a big mistake in interpretation.
Presentation of Data
What units of measure do you feel comfortable with? Do you prefer graphic results, high and low distinctions or an actual value found?
Soil reports come in all shapes and sizes. Some reports are very colorful and show your results in a graphic form. Various reports show values as low, adequate, or high. A number of reports show actual values found for each parameter. Reporting styles also vary regarding the reporting of desired levels, sufficiency levels and base saturation percentages. What style are you most comfortable with? A combination of these styles may be most helpful.
Units of measure can vary from parts per million, pounds per acre, pounds per 1,000 square feet, or kilograms per hectare.
It is very important that the laboratory is aware of your sampling depth if you will be receiving your results in a pound per acre or pound per 1,000 square feet format. The sampling depth will affect the value reported. It is vital to be aware of units when comparing reports from different laboratories. You have to compare apples to apples. Looking at a phosphorus example again will explain this. A laboratory may report phosphorus at 50 ppm P and another may report it at 229 pounds per acre P2O5. These two results are the same; however the units are the difference.
Does the soil report offer a recommendation? Where did it come from? Some recommendations are generic computer recommendations that give a ballpark range for optimum levels of nutrients. These may or may not be for a specific geographical area. If you are growing a unique or exotic crop, then you may need some specific advice. Inquire about the services of an independent agronomist.
How do you get your sample to the lab? Most labs will provide a soil sample bag or suggest a suitable alternative. Soil laboratories receive hundreds of samples each day. Be sure to acquire the appropriate paperwork from the laboratory to submit with your sample. Incomplete information will only delay the processing of your samples. Packing your samples for shipment is very important. Be sure to pack the samples tightly in a box. Pack newspaper or other packing material around the samples to keep them from bouncing around in the box.
If samples can move around during shipment, they sometimes break open and can be destroyed. Resampling will add to your cost in time and money.
How long will this process take? Turnaround time in the whole soil testing process is imperative. Laboratories under stand that your test results can be time sensitive. Don’t hesitate to contact the lab if you have an emergency situation and need “rush” service. To determine your approximate turnaround time, consider the time it takes to get the sample to the lab (two-three days) and perform the analysis (three-four days).
Turnaround time varies from one lab to another and also varies by season. You may want to contact the lab to inquire about their current turnaround time. How do you get your report? You do not want the report held up somewhere after you have already waited through shipping and testing procedures. Reports are usually emailed or made available on the internet on the same day the testing is completed. Be sure your correct email address and/or a fax number is submitted with your samples to get your results as soon as possible.
This is just the tip of the iceberg when looking at differences in laboratories. Laboratory instrumentation is continually improving. More parameters can be detected in a short amount of time and detection limits keep getting smaller. More efficient and “green” procedures are always being investigated.
Embrace the advancements. Visionaries like Dr. Albrecht are still being cited in soil analysis circles. If he was continuing his research today, I believe he would embrace the latest technology and tools available.
So, the question still looms … which laboratory is best for you? Take the time to do your homework. It will be worth the investment and you will receive the value that you expect. Explore laboratory websites, call a lab and ask some questions, ask your friends about their experiences. Make sure you acquire the appropriate paperwork and instructions from the lab that you choose.
When you have selected a laboratory that meets your needs and you are comfortable, stick with it. Jumping from lab to lab will only discourage you on your quest to improving soil fertility.
Editor’s Note: This article appeared in the October 2011 issue of Acres U.S.A.