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Are you smarter than a lab Nerd?? Soil Texture 101 At Turf Diagnostics & Design soil texture is a topic of every day conversation. Most of the soils that come in to our lab will undergo a soil textural examination. It’s most often performed along with a particle size analysis. Thus our Smarter than a Lab Nerd questionnaire will focus on determining the composition of sand, silt and clay in a soil sample. Question 1 If you shake a cylinder containing water, silt and clay, do you know which particles will float? Which particles will sink? In a well-shaken cylinder both types of particles will at first float. Over-time the silt particles will be the first to sink to the bottom, while clay particles remain floating. The silt particles are larger in size, thus the first to sink. Question 2 Sand particles are larger than silt and clay particles. What size sieve is used to separate sand from silt and clay? Okay, perhaps question 2 shouldn’t be on this quiz. It’s a trick question! How soils are classified depends upon what the soil is to be used for, and whom the soil is being tested for. Laboratories that work in the field of agronomy use a sieve with 0.05 mm openings (#270 sieve) to separate sand from finer textured particles. The US Department of Agriculture soil texture classification scheme indicates that silt particles are 0.05 - 0.002 mm in size. Clay particles are less than 0.002 mm. Engineering related testing procedures typically use a larger sieve. The #200 sieve (0.075 mm openings) is most often used, as directed by the American Association of State Highway and Transportation Officials (AASHTO). Question 3 What is the difference between a wet sieve and a dry sieve analysis? No, this is not another trick question. Dry sieving is where a dried sample (usually oven dried) is separated via mechanical agitation over a sieve or set of sieves. Wet sieving is a procedure where soil is washed with water over a sieve. In a USDA soil texture analysis, the sample is washed over the #270 sieve to help facilitate removal of the silt and clay from the larger particles.
Photo on the left is a top view of the sieve stack used for a USDA/USGA particle size analysis, and photo on the right is the nest of sieves loaded on to a mechanical shaker. In a nested stack of sieves, the sieves are stacked with largest holes at the top and decreasing size openings as you move down the stack. It’s been a tough quiz, so only one more question. Question 4 Why do we think this is important to you? Soil is literally the building block for every landscape. Soil texture helps us to understand how a soil will perform. Thus, a better understanding of soil physical properties can benefit turf managers, construction managers, suppliers, and designers. This type of knowledge is crucial when evaluating soils. For example, a soil that is high in silt and clay will pack tighter and drain slower than a sandy soil. Consequently a fine textured soil may be highly desirable for a baseball infield, but it probably won’t make a good golf green. Understanding that the “same” test can be performed using different techniques is also important. When reviewing test reports from different labs it’s not unusual to see differing, some times conflicting, results. Perhaps the difference in results is due to testing procedure differences. For example, most sand plants perform a dry sieve test when determining the particle size of their products. USGA and other agronomic testing methods require the use of a chemical dispersant and the wet sieve technique when performing particle size testing. While dry sieving is an effective method for separating larger particles, the dispersant along with the flowing water flushes fine particles much more efficiently. A dry sieve analysis will typically show a lower content of very fine sand, silt, and clay than what is obtained using the wet sieve method. This difference in technique gives differing results that can be crucial in evaluating sands for topdressing (minimal silt & clay preferred) or other uses. Hope you enjoyed the quiz. Of course, it doesn’t really show whether you’re smarter than a lab nerd. We all have our areas of expertise, and at Turf Diagnostics & Design we hope that our expertise helps you to have more success in your efforts. Please contact us whether you are in need of testing or simply need someone to discuss issues related to soils, aggregates, or turf. Whether you’re working on a synthetic turf field, golf course, green roof, or other landscape, we have testing services that can help. We look forward to hearing from you! A Sample With High Organic Content
Our lab had a very interesting surprise in a recent sample. Apparently a lizard had selected one of our customer’s (who shall remain nameless) stockpiles as his burrowing place for the winter. Unfortunately for the lizard, he was in a location that became part of a one-gallon sample that was shipped to our lab. After getting over the shock of finding a live lizard in a sample, we used extensive reptilian identifying techniques (also known as a simple internet search), to determine that our new friend is a male western fence lizard. The stowaway is doing fine in his new home, but we prefer to receive samples that are animal - free. |
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