As the community might have guessed, the Delaware Soil and Water Conservation District has a few soil nerds on staff. We just love sharing our fascination with soil in hopes that you will be as enthralled as we are. In our last column, we discussed soil and what an amazing resource it is. In this column we will “dig” into soil texture.
Soil is a mixture of minerals, dead and living organisms (organic materials), air, and water formed in layers, called horizons. Soil scientists study these layers to describe and delineate properties amongst the more than 400 different kinds of soil in Ohio. (Yes, colleges offer courses and degrees in soil science!) One of the important soil properties is texture – the size and proportion of sand, silt, and clay particles found in a particular soil. Soil scientists describe and record the textures of each horizon, going down to a depth of 80 inches, when possible, or to the depth of bedrock.
Soil texture can be estimated in the field by feel or in a lab using precise measurements. You can try to figure out the texture of your soil using the “feel method” by taking a handful of moist soil and seeing where it falls in these categories:
• Sandy soils do not form a ball when squeezed in the hand. The soil feels gritty, and you can easily see the particles without a microscope.
• Silt feels like flour and forms a ball that easily breaks apart. You can also try making a “ribbon” by placing the ball of soil between your thumb and the side of your forefinger and gently pushing the soil forward with your thumb. Silt will form a ribbon of soil only one to two inches long.
• Clay is the smallest soil particle and can only be seen through an electron microscope. It is sticky when wet and easily forms a ball. It will also form a strong ribbon at least two inches long.
In a lab, the percentages of sand, silt, or clay in a soil are determined by measuring the relative rates at which the different particle sizes settle in a liquid due to gravity. These precise measurements are then recorded in the Web Soil Survey by the USDA Natural Resources Conservation Service (www.nrcs.usda.gov/wps/portal/nrcs/oh/soils/surveys/), along with other details such as the depth to the water table, landform, slope, color, and drainage class.
A fun and inexpensive way to make your own “home soil lab” using your soil, a colander, water, dishwasher soap, and a clear jar with a lid can be found at https://hgic.clemson.edu/factsheet/soil-texture-analysis-the-jar-test/. A simple worksheet helps you calculate the percentages of sand, silt, and clay and those numbers are then located on the USDA’s soil texture triangle diagram (worksheet and diagram included). This is an excellent hands-on and inter-disciplinary activity to do with kids.
Soil particles are very small, but here is a way to visualize and compare them. A large clay particle would be the size of a pea, silt the size of a ping pong ball or larger, and a grain of sand would be as big or bigger than a basketball. Why should we care about soil texture and their percentages? Soil texture determines how fast or slow water drains through a soil. It also determines how much water each soil can hold that can be used by plants. Sandy soils tend to hold little water but allow good aeration. Clay particles are very small in size and tend to pack down so that water does not drain well and little to no air can penetrate, resulting in poor growing conditions for plants. Silt falls between sand and clay in terms of its properties. Loamy soil is often referred to as the most desirable but what does that really mean? Loamy soil is a combination of sand, silt, and clay in relatively equal amounts so it holds ample moisture for plants but also drains well, with plenty of air for plant roots.
We can’t live without sun, air, water and soil. Soil is the skin of the earth, but we rarely see more than its surface, and even that is usually covered up by buildings, pavement, crops, grass and trees. Not all soil is the same as any good farmer or gardener can tell you, so learn more about your soils! We will even let you join us in the soil nerds club. Check out all of our programs and materials at soilandwater.co.delaware.oh.us and visit us during the Delaware County Fair.
Bonnie Dailey is deputy director of the Delaware Soil & Water Conservation District. For information, go to https://soilandwater.co.delaware.oh.us/.