APES-“Soil Lab” Introduction: Soil consists of rock particles, water, dissolved chemical substances, decaying organic matter, and a large assortment of microorganisms, plants, and animals. Therefore, the soil constitutes an important type of ecological community. In this lab, you will explore the physical and chemical makeup of a soil sample. Part I-Soil Texture Background: Through the process of weathering, rocks are weathered into fine particles of clay (<0.002 mm in diameter), silt (0.002 to 0.05 mm), and sand (0.5 to 1.0 mm). The relative amounts of the different sizes of particles control two very important properties of soil; its fertility and its ability to hold water. Soil fertility is measured by the amount of nutrients available for plant growth. These nutrients in soils are usually found in the form of positively charged ions, such as sodium, calcium, and potassium. Since the very small particles of clay (called micelles) often have a negative charge, these ions can be held in the soil on the surface of the micelles. The larger particles of silt and sand do not have this negative charge. Therefore, soils with more clay tend to be more fertile. The infiltration and retention of water in a soil are also important. Soils with low infiltration, such as clay, are more likely to have a high runoff after rain and the potential for flooding. Yet these soils can retain a good deal of water. In contrast, sandy soils have very high infiltration rates, but are unable to retain much water (most of the water flows through the soil to the water table). High infiltration can result in leaching, the loss of nutrient ions from the layers of the soil where roots are most abundant. These soils are likely to be infertile, and the leachate can have high concentrations of nutrients and pesticides, polluting both the groundwater and adjacent rivers and lakes. The “best” soils, called loam, are a mixture of sand, silt, and clay. These soils contain the best of each of the textural components and have relatively high fertility and a relatively high water-holding capacity. Procedure (Part 1): 1. Soil Texture Triangle • Examine Figure 1, which shows the classes of soil textures based on their percentage proportions. • Read the accompanying explanation to determine how the composition of Point A was determined, and in which category it was placed. Pre-Lab Questions: • Determine the name and percent composition of points B, C, D, and E. • Write your answers to the above in your lab notebook. Procedure (Part 1.2 continued): 2. Qualitative Soil Test – Visual Identification Obtain a soil sample from home. • Note its general color and appearance. Look at your soil through a magnifying lens. Note the color, the size, and shape of the particles, describing as many as you can. Try to identify the organic material that might be present. • Record your qualitative observations in Data Table. 1 3.

Qualitative Soil Test – Ribbon Test • Using the flow chart called “Estimating Soil Texture,” and the “Diagram for Estimating Soil Texture,” (Figure 2) perform the ribbon test to: i. determine the texture of your soil sample ii. place an “X” on Figure 2 to indicate its approximate location iii. refer to Figure 1 to determine approximate percentages of sand, silt, and clay for your sample. • Record all results in Data Table 2.

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Quantitative Soil Test ▪ Fill a jar ¾ way full with your soil. ▪ Add enough water to saturate the soil completely and then keep adding water until the level gets to near the top. ▪ Now, place a lid on your jar to seal it and carefully shake the jar until the soil and water completely mix to make a free-moving slurry. Be sure to break up any lumps in the soil. Do this for at least one minute. ▪ Now, label the jar with tape and place the jar on the back table for 24 hours, to let the soils settle out. The denser, larger sand particles will settle out first and be on the bottom of the cylinder. A layer of silt will settle out on the top of the sand, and finally, after 12-24 hours, the tiny clay particles will settle out on top of the silt. ▪ Refer to Figure 1 to determine approximate percentages of sand, silt, and clay for your sample. ▪ Record your results in Data Table 3.

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Part I Lab Discussion/Analysis Questions ▪ Discuss the answers to Part I analysis questions 1-7. 1. What is meant by soil texture? 2. What role does sand play in determining soil fertility? 3. Explain the role of clay in determining soil fertility? 4. What role does sand play in the growth of plants? 5. What problems can occur in a soil that has: ◦ Too much sand? ◦ Too much clay? 6. Summarize the physical characteristics of your soil sample as observed under the magnifying lens (Procedure Part I.2). Using your observations and the soil texture triangle, what type of soil do you have? 7. Using the data from Procedure 4 of Part I (quantitative soil test) and your soil texture triangle, what type of soil do you have? How does this compare to the qualitative results (Procedure 2)?

Figure 1 – Soil Texture Triangle

D B C E

Figure 2 - Estimating Soil Texture (Ribbon Test)

Part 2-Chemical Composition: Background: Soil offers a unique environment to examine the interaction between the environment and living things. All of the organisms which live in or on the soil interact with the chemical constituents of the soil. Organisms are influenced by their chemical environment, and they also determine to some extent what that environment will be. In this part of the lab, you will perform a series of tests to acquire a comprehensive qualitative analysis of the chemical composition of a soil sample. The pH of soil is an important factor in determining which plants will grow because soil pH controls which nutrients are available for plants to use. The actions of plants, animals, and microbes that inhabit soil, along with physical factors, especially the characteristics of rainfall in the area, affect soil pH. Contrary to popular belief, rainwater does not have a pH of 7.0. As raindrops fall through the troposphere, carbon dioxide (CO2) is absorbed and dissolves in the rainwater, as a result the raindrops become acidic as CO2 reacts with water to form carbonic acid (H2CO3), as shown below. CO2 + H2O --> H2CO3 Since air has always contained CO2, rain has always been acidic. Today, the pH of rain can be 5.0 or lower if it is contaminated with oxides of sulfur and nitrogen which can form sulfuric and nitric acids respectively. In this lab activity, the pH of a soil sample will be determined. Procedure: 1. Follow the instructions in the soil test kit to perform the pH test, Nitrate, Phosphate, and Potassium tests on your soil sample. Record results in your Data Table 3. Data Analysis: Answer analysis questions 1-12 in your lab notebook. These questions will require research from online sources, book, and notes. 1. How are plants affected by the pH of the soil? 2.

How is the pH of the soil influenced by plants?

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Why is important to know the pH of the soil?

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How can the pH of the soil be adjusted?

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Discuss the role of nitrogen in promoting plant growth.

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Discuss the role of potassium in promoting plant growth.

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Discuss the role of phosphorus in promoting plant growth.

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Based on the results of Part II, what conclusion would you reach about the fertility of our soil samples? Support your answer with data obtained from the tests you performed. Which topsoil sample had the best fertility? Why?

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If fertilizers are applied to soils already rich in nutrients, they can not be absorbed by the plants. What happens to them and what environmental consequences will result?

Conclusion: Write a detailed conclusion in your lab notebook referring back to your hypothesis, data analysis answers and referring to the results of your soil tests.