ENV111SoilLab

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Dec 6, 2023

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Virtual Lab Exercise on Soils, Drainage, and Runof Desiree Casablanca-Bentz Dierdre Hall ENV 1111 16 March 2023 Soils, Drainage and Runof INTRODUCTION Soil is a thin layer on top of most of Earth’s land surfaces. This thin layer is a precious natural resource. Soils so deeply affect every other part of the ecosystem that they are often called the “great integrator”. Soils hold nutrients and water for plants and animals. Water is filtered and cleansed as it flows through soils. Soils affect the chemistry of the water and the amount of water that returns to the atmosphere to form rain. The foods we eat and most of the materials we use for paper, buildings, and clothing are dependent on soils. Understanding soil is important in knowing where to build our houses, roads, and buildings as well as understanding environmental impacts. Soils are composed of three main ingredients: minerals, organic materials from the remains of dead plants and animals, and pores that may be filled with air or water. A good quality soil for growing plants should have about 45% minerals, 5% organic matter, 25% air and 25% water. Soils are dynamic and change over time. Some properties, such as soil moisture content, change very quickly (over hours), while other changes, such as mineral transformations, occur very slowly (over thousands of years). Soil formation and the properties of the soils are the result of five key factors. These factors are: 1. Parent material : The material from which the soil is formed. Soil parent material can be bedrock, organic material, or surface deposits from water, wind, glaciers, or volcanoes. 2. Climate : Heat and moisture break down the parent material and affect the speed of the soil processes. 3. Organisms : All plants and animals living on or in the soil. The dead remains of plants and animals become organic matter in the soil, and the animals living in the soil affect the decomposition of organic material. 4. Topography : The location of a soil on the landscape can affect how climatic forces impact it. For example, soils at the bottom of a hill will be wetter than those near the top of the slopes. 5. Time : All of the soil forming factors above assert themselves over time – from hundreds to tens of thousands of years. SOIL PROFILES Due to the interaction of the five soil-forming factors, soils differ greatly. Each soil on the landscape has its own unique characteristics. The way a soil looks if you extract a core sample is called a soil profile . 1

Virtual Lab Exercise on Soils, Drainage, and Runof The soil profile can be used to determine the properties of the soil and the best use of the soil. Every soil profile is made up of layers called soil horizons . Horizons can be identified by changes in color or texture compared to adjacent horizons. Horizons are labeled based on their properties. O horizon : The O-horizon is made up of organic material. The horizon is found at the soil surface. A horizon : The A-horizon is commonly called the topsoil and is the first mineral horizon in the soil profile. The A-horizon is mostly made up of sand, silt, and clay particles, but also contains some decomposed organic material. B horizon : The B-Horizon is composed of mineral materials that are undergoing chemical and physical weathering. Weathering causes changes in soil color, texture, and structure. The B-horizon is often rich in clays, iron, and aluminum. C horizon : The C-horizon is the parent material from which the horizons above have formed. SOIL TEXTURE One factor that determines a soil’s ability to hold water and resist erosion is soil texture. Soil texture refers to the ratio of different-sized mineral particles in soil. Based on size, mineral particles are referred to as clay, silt, or sand (Table 1). Clay particles are small and electrically charged. They attract and hold onto 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. But 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 (and is generally low in fertility). Exposed sandy soils may be subject to erosion if the angle of the land, the slope, is too severe. Table 1. The Size of Sand, Silt and Clay Name Particle Diameter Clay Below 0.002 mm Silt 0.002 to 0.05 mm Very fine sand 0.05 to 0.10 mm Fine sand 0.10 to 0.25 mm Medium sand 0.25 to 0.5 mm Coarse sand 0.5 to 1.0 mm Very coarse sand 1.0 to 2.0 mm Gravel 2.0 to 75.0 mm Rock Greater than 75 mm 2

Virtual Lab Exercise on Soils, Drainage, and Runof One method of classifying soils is to measure the relative amounts of sand (gritty), silt (dusty), and clay (fine and sticky) in a soil sample, then use a soil triangle to determine the soil type (Figure 1). Figure 1. Soil Texture Triangle. This triangle illustrates the 12 USDA soil classifications and is commonly used in classifying soil textures. Goal 1: Classify soils by grain size Watch this video first to learn how to use the soil texture triangle: https://www.youtube.com/watch?v=y4xndouxWPY 1. If a soil survey tells you that you have a ‘sandy clay loam’ on your property, what does your soil have in most abundance: sand, silt or clay? A “sandy clay loam’ would be abundant in sand. 2. If you send your soil out for a test and find out that it contains 75% silt and 25% clay, what kind of soil do you have? Your soil would be categorized as a ‘silt loam’ of it were 75% silt and 25% clay. 3

Virtual Lab Exercise on Soils, Drainage, and Runof 3. Pure loam is the best kind of soil for a farm or garden and is often defined as a soil with roughly equal proportions of sand, silt, and clay. Is that what the diagram shows? If not, what does it indicate? If I place 1/3 of each type of soil on the diagram, they intersect in the ‘clay loam’ portion of the diagram. 4. Use the soil triangle to determine the type of soils with the following particle sizes: a 20% silt, 10% clay, 70% sand sandy loam b 30% sand, 10% clay, 60% silt silt loam c 10% silt, 50% sand, 40% clay sandy clay d 30% clay, 30% sand, 40% silt clay loam e 60% clay, 10% sand, 30% silt clay f 40% sand, 10% silt, 50% clay clay Goal 2: Soil drainage experiments In this section we will examine how diferent soil types influence drainage. This is simulated data and the idea is that water was been added to a funnel full of the particular soil type. The last column corresponds to the total amount of water that had to be added before any water was able to drain through the soil. Soil Type Percentages Amount of water needed to drain (mL) Sand Silt Clay Heavy Clay -- -- 100 58 Silty Clay 0 50 50 54 Silty Clay Loam 0 70 30 52 Silt -- 100 -- 39 Silt Loam 30 70 0 41 Loam 40 20 20 45 Sandy Loam 60 20 20 37 4

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