2054 Lab C Why Is Soil Texture Important? Introduction: Soil texture refers to the ration of different-sized mineral particles in soil. Based on size, mineral particles are referred to as clay, silt, or sand. Clay particles are small and electrically charged and attract and hold water molecules. Thus, it is important that soils used to grow crops have some clay content. Clay also helps make soil resistant to erosion. Like clay, silt particles are also small enough to hold water in the soil. However, exposed silt washes away easily, taking nutrients with it. A soil with too much sand content allows water to pass through very quickly and does not hold enough moisture to support most plants. Exposed sand soils may be subject to erosion if the angle of the land, the slope, is too severe. Objectives: To determine the texture of a soil sample you collect and analyze it to determine the percents of clay, silt and sand. Materials: 1 20 ounce pop bottle with cap tap water soil sample newspapers large funnel spatula or spoon cardboard Procedure: 1. Collect 250ml of soil A. Collect the sample from the top 2-4 inches of soil B. Label the sample with your name, date, and collection site. C. Also on the label, describe the following features of the collection site: a. Slope b. Amount and type of vegetation c. Moisture level d. How the land is being used 2. Crumble you sample into small pieces, breaking up any large clods. 3. Spoon enough loose soil from your sample to fill your bottle half full. 4. Fill the bottle almost to the top with tap water. 5. Cap the bottle and shake it. Be sure the cap is screwed on tightly before you shake the bottle and that your hands are dry. Allow the mixture in your half pint bottle to settle until distinct layers of soils have formed beneath the water. A. When the sample is well mixed, place the bottle upright on the lab table. B. Describe the appearance of you soil sample on line A of Data Table 1 Note: Some soils may take several hours to settle, particularly if they include large amounts of clay. If your sample hasnt formed distinct layers after 20 minutes, label it and keep it until the next lab period. Continue the lab using a different soil. 6. Hold a piece of cardboard next to the half-pint bottle. A. Draw horizontal lines on the cardboard box to mark the soil layers.
B. C.
Next to each layer write the type of soil particle found in that layer: clay, sand, silt. Perform the calculations in the next section to fill in Lines B, C, D, and E of Data Table 1.
Observations and Data Collection: DATA TABLE 1 A. How did your sample look after you mixed it with water?
B. C. D.
% sand silt % % clay
__________% __________% __________%
E. Soil type for your soil sample Calculations: 1. Using the formula below, calculate the % of each type of soil (sand, silt, clay) in the soil in the soil column of your half-pint bottle. Depth of sand layer in mm % sand = total depth of soil in mm X 100% 2. Using the %s in Date Table 1 and the soil triangle included in the lab, determine the soil type for you sample as follows: A. Find each % on the proper axis of the soil triangle. B. Follow the dotted lines from each % to the point where they intersect in side the soil triangle. C. Identify your soil type by identifying the region of the soil triangle that contains the point of intersection. (For example, for a soil with 50% sand, 30% silt, and 20% clay, the 3 dotted lines intersect in the region marked loam) D. If the dotted lines intersect on the boundary between two regions, assign the soil type f the graph region of greater area. Cleanup Instructions: 1. Save you soil sample for use in another lab. A. Seal the plastic bag containing the remainder of your soil sample. B. Add the soil type label you made for your sample in Step 1. C. Store the sample as directed by your teacher. 2. Do not empty your half-pint bottle directly into the sink. A. Form a filter cone from several sheets of newspaper. B. Place the cone in a large funnel. C. Place the funnel in the sink drain. D. Empty you half-pint bottle into the cone.
E. F. G. H.
Fill the bottle with clean water and again empty it into the cone. Repeat the rinsing process as needed until the soil particles are ...