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Sandy Loam or Loamy Sand?
Why would you want to know whether your soil is considered a clay loam or loamy clay, for example? These terms describe the texture of soil, which is determined by the size of the basic particles it is made of. You may want to know because you are reading what soils are best for growing a particular plant, or what soil treatments will improve your gardening success. Fine textured soils require more lime or sulfur to change the pH and they retain nutrients better so that fertilizer may be applied less often. Water moves through various soil textures differently so that affects the design of irrigation and drainage systems. Lines must be closer together in some soils, increasing the cost.
RELATIVE SIZE OF SOIL PARTICLES
| sand 2 - .05 mm
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. silt .05 - .002 mm . clay < .002 mm |
The standard MSU soil test lab reports used to contain a comment on the soil texture, but now an accurate measurement of texture is an extra-cost option. It is not hard to measure it yourself, though, accurately enough for most homeowner concerns. Below this triangle graph is a simple step-by-step method of measuring the percentages to find your soil texture:
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A soil texture triangle is used to classify the texture class of a soil. The sides of the soil texture triangle are scaled for the percentages of sand, silt, and clay. Clay percentages are read from left to right across the triangle (dashed lines). Silt is read from the upper right to lower left (light, dotted lines). Sand from lower right towards the upper left portion of the triangle (bold, solid lines). The boundaries of the soil texture classes are highlighted in blue. The intersection of the three sizes on the triangle give the texture class. For instance, if you have a soil with 20% clay, 60% silt, and 20% sand it falls in the "silt loam" class. |
Collect a pint or quart sample of soil; cores or plugs as deep as you generally till the garden are best if plant preferences are your reason for measuring. Spread them out on trays or newspapers to dry. Sift the dry soil through a screen or an old colander to break up lumps. Choose a glass jar with a tight-fitting lid and straight sides with at least a quart or two capacity. Taller jars make measuring easier and more accurate. Fill it half full of the dry, screened soil and add a tablespoon of powdered detergent such as for dishwashers. This helps separate and suspend the particles.
Fill to an inch from the top with water and shake vigorously for 3 minutes to make sure the soil is not clumping and sticking inside the jar. Set it on a level surface and measure with a ruler how much settles in the first minute. (Calculating will be easier if you measure in millimeters instead of inches and fractions). Measure carefully at eye level and record your measurements for later calculations. This will be the sand layer, and will appear coarser so you can tell it later from the silt that settles next. Wait just one hour and measure again to the top of the sand layer, and then measure how many more millimeters up to the top of the silt layer. (You can use either the first or second measurement for the sand, whichever seems best to you…they should be very close.)
Wait until the water clears, a whole day or two, then measure the final layer, from the top of the silt to the top of all the solids. Add the measurements together for the total height of soil solids. Divide each measurement by the total to obtain the percent, such as if there were 26 mm of sand in 60 mm of solids, 26/60 = 43%. Then use a Soil Texture Triangle such as the one on this page to find the spot with the same percentages of sand, silt and clay as your soil. Start by finding the clay percentage on the edge of the triangle and draw a line to the right. Then from the silt percentage, draw a line down and to the left. From the sand, draw up and to the right. Where the lines intersect in the middle, the texture is described.
Further example for illustration:
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level of water
total solids 70 mm |
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Measurements
Clay up to 70 mm 70-55=15mm Silt up to 55 mm 55-45=10mm Sand up to 45 mm |
| Divide by total: | Clay 15/70 = 21 % Silt 10/70 = 14 % Sand 45/70 = 65 % | From texture triangle, this is Sandy Clay Loam |