Name: Part I: Soil Texture DIRT! APES Laboratory Activity Can one determine the texture of soil by examining the particles found in a particular sample? The purpose of this activity is to determine the amount of sand, silt, and clay in a given soil. This additional method of determining the profile of soil is to conduct a profile test using a soil sieve to separate out the different particles by their relative size. Soil is made of both living and dead plants and animals (organic matter) and mineral particles such as sand, silt, and clay. It is said to consist of rocks and minerals (about 45%), water (25%), air (25%), and organic matter (5%). The profile and texture of soil indicate the relative types of rocks and minerals that compose the soil, chief of which are sand, silt, and clay. Soil texture is an important indicator of the ability of soil to absorb and hold both water and plant nutrients. Soil type can be classified as follows: Soil Types by Percentages:! Sands: 85-90% sand and <10% clay and silt! Loamy Sands: 70-85% sand and <15% clay! Sandy Loams: >52% sand and <20% clay! Loam: 7-27% clay, 28-50% silt, and <52% sand! Silt Loam: >50% silt, 12-27% clay OR 50-80% silt and <12% clay! Clay Loam: 27-40% clay and 20-45% sand! Clay: 27-40% clay and less than 45% sand and less than 40% silt Estimating Soil Texture by Feel: Materials:! Your fingers!! Water! Light- colored soil sample! Dark- colored soil sample Instructions: Take a small moist wad of your soil sample and squeeze it between your thumb and fore finger. If it feels gritty, then you have mostly sand. If it feels sticky, then you have mostly clay. If it feels neither gritty nor sticky, then you have mostly silt. If you can squeeze out a long, unbroken ribbon of soil from your fingers, you have clay. If you can squeeze out a short ribbon, you have silt or loam. If you cannot form a ribbon, then it is sand or sandy loam. Analyzing & Concluding: 1. What kind of soils do you have? a. Light- colored soil: b. Dark- colored soil: 2. Why would we do more than one type of test to determine soil type?
Determining Soil Texture by Soil Sieve: Materials:! Weighing paper! Balance! Soil Samples (light- colored and dark- colored samples)! Soil Sieves (#6, #20, #40, and #100)! Weighing paper and/or trays Instructions: 1. Place your weighing paper on the pan of the balance and press the tare button to make the balance read zero grams. 2. Arrange the soil sieves so that the largest screen size is on the top, followed by decreasing screen size to the bottom. 3. Weigh out about 30 g of soil (light- and dark- colored soils). 4. Place your first soil sample into sieve tube. Shake your sample over the sieves for a couple of minutes so that the particles fall through all of the screens. 5. Place the remaining soil from sieve #1 on the weighing paper and record its mass. Record this on your data table. 6. Repeat with sieve #2, #3, #4, and the bottom container. 7. Calculate the relative percent of gravel, sand, silt, and clay in the soil sample and record your data in the table below. For example, you can calculate the percent gravel by the following calculation: % Gravel = mass of gravel/total soil mass x 100 8. Determine the type of soil based on the relative overall percents you calculated. 9. Repeat the process with the other soil type or swap information with the other group. 10. Answer the conclusion questions and clean up your materials. Table 1 Determining Soil Texture by Sieve LIGHT- COLORED SOIL DARK- COLORED SOIL Sample Mass measured Soil percentage Mass measured Soil percentage Weighing Paper Total Soil Sample Sieve #1 Gravel Sieve #2 Fine Gravel Sieve #3 Coarse Sand Sieve #4 Fine Sand Bottom Container Silt & Clay Type of soil for sample collected: Light- colored soil: Dark- colored soil: Analyzing & Concluding: 1. How do the light- and dark- colored soil sample textures compare? 2. How would the size of soil particles affect the ability of soil to hold moisture?
3. Which type of soil would be most likely to allow for the greatest amount of groundwater beneath the soil? Explain your choice. 4. Why might trees and other terrestrial vegetation have difficulty growing in sandy or gravel- like soil? 5. Why would a soil texture analysis be important not only to an ecologist, but to a construction or highway engineer? 6. What types of minerals do you think would be helpful to add to soil to make it a healthier substrate for plant growth? 7. What kind of conclusions have you drawn about the history of the soil sample: its parent material, erosion (including which types of agents, how long, and what climates), and finally, its environment of deposition. (Do your best, this question is tricky and requires educated guesses, exactly what real geologists have to do!) Part II: Soil ph When you think of ph, you probably think of acidic and basic solutions. But soil can be acidic or basic, too. Soil ph, sometimes referred to as soil acidity, can be expressed using the ph scale. The ph scale ranges from 0 to 14. Soils with ph above 7 are basic or sweet. Soils with ph below 7 are acidic or sour. A soil with a ph of 7 is neither acidic nor basic, but is neutral. Macronutrients Nitrogen Phosphorus The ph of soil is an important factor in determining which plants Potassium will grow because it controls which nutrients are available for the plants to use. Three primary plant nutrients nitrogen, Sulfur phosphorus, and potassium are required for healthy plant Calcium growth. Because plants need them in large quantities, they are called macronutrients. They are the main ingredients of most Magnesium fertilizers that farmers and gardeners add to their soil. Other nutrients such as iron and manganese are also needed by plants, but only in very small amounts. These nutrients are called micronutrients. Plant Nutrients Micronutrients Iron Manganese Zinc Copper Molybdenum Cobalt Chlorine The availability of these nutrients depends not only on the amount but also on the form that is present, on the rate they are released from the soil, and on the ph of the soil. In general, macronutrients are more available in soil with high ph and micronutrients are more available in soil with low ph. The figure to the right shows the effect of ph on the availability of nutrients in the soil.
Materials:! Vernier LabQuest! Vernier ph Probe! Soil samples (light- colored & dark- colored sample) Instructions: 1. Prepare the water- soil mixture.! 200 ml beaker! 100 ml graduated cylinder! distilled water! spoon/stirrer! 0.01 M CaCl 2 a. Place roughly 20 g of soil into a 250 ml beaker. b. Add about 40 ml 0.01 M CaCl 2 and stir thoroughly. c. Stir once every two minutes for about 6 minutes. d. After the final stirring, let the mixture settle for about five minutes. This allows the soil to settle out, leaving a layer of water on top for you to take your ph measurement. Proceed with Step 2 while you are waiting. 2. Connect the ph Sensor and the data- collection interface. 3. Remove the buffer container from the end of the sensor, careful not to spill the contents. Rinse the ph Sensor with distilled water using a pipette. 4. Measure the ph. a. Carefully place the tip of the ph Sensor into the liquid part of the beaker contents. Make sure the glass bulb at the tip of the sensor is covered by the water. Stir gently. b. Continue gentle stirring. Note and record the ph value when the reading stabilizes. 5. Rinse the ph Sensor with distilled water and return it to its storage container. 5. As a comparison for accuracy, now use the ph strips to measure the ph of the water- soil mixture. Analyzing & Concluding: 1. What is the ph of the light- colored soil sample you tested? Compare the ph Sensor reading to the ph strips. 2. What is the ph of the dark- colored soil sample you tested? Compare the ph Sensor reading to the ph strips. 3. Are the soil samples classified as sweet, sour, or neutral? 4. How is soil ph important to plants? 5. How is soil ph important in a discussion of the acid deposition and its influence on plant growth?
Part III: Soil Permeability Materials: Procedure: A soil's permeability is a measure of the ability of air and water to move through it. Permeability is influenced by the size, shape, and continuity of the pore spaces, which in turn are dependent on the soil bulk density, structure and texture. Most soil series are assigned to a single permeability class based on the most restrictive layer in the upper 5 feet of the soil profile (Table 1). However, soil series with contrasting textures in the soil profile are assigned to more than one permeability class. In most cases, soils with a slow, very slow, rapid or very rapid permeability classification are considered poor for irrigation. Soil Permeability Classes. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Infiltration Rate Classification (inches/hour) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Very Slow Less than 0.06 Slow 0.06 to 0.2 Moderately Slow 0.2 to 0.6 Moderate 0.6 to 2.0 Moderately Rapid 2.0 to 6.0 Rapid 6.0 to 20.0 Very Rapid Greater than 20.0 Infiltration is the downward flow of water from the surface through the soil. The infiltration rate (sometimes called intake rate) of a soil is a measure of its ability to absorb an amount of rain or irrigation water over a given time period. It is commonly expressed in inches per hour. It is dependent on the permeability of the surface soil, moisture content of the soil and surface conditions such as roughness (tillage and plant residue), slope, and plant cover. Coarse textured soils such as sands and gravel usually have high infiltration rates. The infiltration rates of medium and fine textured soils such as loams, silts, and clays are lower than those of coarse textured soils and more dependent on the stability of the soil aggregates. Water and plant nutrient losses may be greater on coarse textured soils, so the timing and quantity of chemical and water applications is particularly critical on these soils. 2 Plastic or Styrofoam cups 2 Soil samples 50 ml beaker 50 ml graduated cylinder 1. Take one of the plastic or Styrofoam cups and poke three holes in the bottom. 2. Fill the plastic cup with the holes half way with one of the soil samples. Pack it down lightly so that there are not large air spaces. 3. One of the lab partners will hold the cup with the soil above the cup that has no holes and is empty so that they can catch the water as it drips through the soil.
4. The other lab partner will measure out 50 mls of water and slowly pour it on top of the soil. 5. Time for 1 minute and then set the cup with the soil aside. (Be careful, it will still drip water, so put it in a sink or over a cup or beaker). 6. Pour the water from the cup into the graduated cylinder to see how much of the 50 mls came through. 7. Record the amount in the chart below and repeat the procedure for the remaining two soil sample. Volume of Water (ml) Light Soil Sample 1 Dark Soil Sample 2 Analysis: 1. Could the size of the soil particles affect life of microorganisms living in the soil? 2. Which soil sample contains the most clay? Sand? 3. Why would a farmer need to know the soil permeability on his land? 4. Which of the soil samples held more water and why?