Soils Online Laboratory

Soils Laboratory Introduction Soil is a mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms (mostly microscopic decomposers). By volume, soil is 45% mineral (from underlying rock, or deposited by glaciers, rivers, ocean currents, wind, or landslides), 25% air, 25% water, and 5% organic matter. Soil is one of our most important natural resources for its obvious role as a growing medium for plants. It also serves important functions in storing and purifying water, decomposing biodegradable wastes and recycling nutrients. Mature soils are organized into layers, called horizons that vary in texture and composition. Each layer has a unique composition and special properties. The uppermost layer is called the O Horizon and is composed of surface litter (fallen leaves, twigs) and humus , which is partially decomposed organic matter. This layer contains millions of organisms, including algae, fungi, bacteria, worms, insects and other macroinvertebrates (animals without backbones that are large enough to be seen without a microscope). Below this layer is the A Horizon , or topsoil, composed of a porous mixture of humus and inorganic minerals. Although several other horizons exist below, these two uppermost layers are most important in terms of soil fertility , or the ability to support plant growth. The roots of most plants are concentrated in the O and A horizons. Soil characteristics that influence fertility include color , texture and porosity . Darker soils contain more organic matter than light-colored soils. Organic matter contains plant nutrients, which are important for growth. Plant growth is often limited by inadequate amounts of nitrogen, phosphorus and potassium (which is the reason most fertilizers are composed of these 3 nutrients). Soil pH is also important, because nutrient uptake may be limited under acidic or alkaline conditions. Different plant species prefer soils of different acidity levels. Soil fertility may be enhanced by adding amendments that can change texture, porosity, pH and nutrient content. Adding peat moss increases soil acidity and water-holding capacity. Compost adds nutrients and enhances texture. Adding sand to clay soils may help increase porosity. Soils with a grayish or greenish color indicate wetland, or hydric soils, which generally have high clay content. These soils may be flooded for months at a time and are not suitable for agriculture or development without large inputs of compost, sandy fill material or chemical fertilizers. Soil texture refers to the size of soil particles. Sand particles are the largest, clay particles are the smallest and silt particles are intermediate in size. Texture relates to porosity , or the amount of air spaces contained in soil. Plant roots need oxygen for metabolic processes. Porosity also indicates how well water will infiltrate and percolate downwards through the soil column. The larger the soil particles, the more porous the soil and the quicker water will infiltrate and percolate. The most fertile soils in terms of particle size are called loams , which are 40% sand, 40% silt, and 20% clay and humus.

In this laboratory exercise, you will examine soil characteristics, including depth of the A and O horizons, color, and texture for a soil in your neighborhood. In addition, you will explore state soils in the United States. All questions, or spaces where you need to supply an answer, are written in red so you can easily find them. Please type your descriptions and answers directly into this file in BLUE so that they are easy for me to find. You will submit this completed file and the photos of you performing different steps of this lab through a CANVAS submission link on your CANVAS course page. II. Activities A. Collect soil sample. 1. Gather the following materials together: ruler, pencil, something to dig with (i.e. spade, shovel, spoon), and a plastic bag. 2. Select a sampling site in your backyard or in nearby area where you are allowed to dig a hole. Describe your sampling site: (Please write your answers in blue) 3. Push away leaves or any debris on top of the soil. Cut into the soil with your digging implement approximately 6-8 inches deep, making a square hole about 6 inches in diameter. Try to pull out this square clump of soil without disturbing the layers. Put your soil sample in a plastic bag so that you can analyze it at home. (take a photo of you with your soil clump at your sampling site, include your face in the photo. Paste the photo here) 4. Measure the height (cm) of O and A layers using your ruler. (take a photo measuring the depths of the soil horizons in your soil pit, include your face in the photo. Paste the photo here.) Height of O horizon (cm): ____________ Height of A horizon (cm): ____________ B. Determine Soil Color of Your Sample Gather the following materials together: 1. Munsell Soil Chart. This can be found as a PDF file online. Here is the link: https://www.southsuburbanairport.com/Environmental/pdf2/Part%204%20-%20References/Reference%2016%20Munsell %20Color%20Charts/MunsellColorChart.pdf ) 2. a bottle of water.

Try to form a "ribbon" by pushing out the soil between your thumb and forefinger (as demonstrated by the instructor). If you cannot form a ribbon, or the ribbon breaks quickly, there is little clay in the sample. Practice making a ribbon for a few minutes, then measure the length (in mm) of the ribbon that breaks off. Do this three times and calculate an average ribbon length (mm) (take a photo showing your soil ball, include your face in the photo. Paste your photo here) Refer to the descriptions of soil texture classifications in Table 1 and estimate your soil texture type based on the most appropriate description and average ribbon length. Table 1. Soil texture classification Texture Classification Description of bolus Ribbon Length Approx. Clay Content Sand Cannot be molded, little coherence, single sand grains stick to fingers nil <10% Loamy Sand Slight coherence ~5mm 5-10% Clayey Sand Slight coherence, sticky when wet; many sand grains stick to fingers; clay stains hands 5-15mm 5-10% Sandy Loam Coherent but sandy to touch; large sand grains visible 15-25mm 10-20% Loam Coherent and spongy; smooth when manipulated; no obvious sandiness or silkiness ~25mm 25% Silty Loam Coherent; very smooth to silky when manipulated ~25mm ~25% Sand Clay Loam very coherent, sandy to touch; some sand grains visible 25-40mm ~25% Clay Loam Coherent, plastic, smooth to touch 40-50mm 20-30% Silty Clay Loam Coherent, smooth, plastic, silky to touch 40-50mm 30-35% Sandy Clay Plastic; can feel sand grains 50-75mm 35-40% Clay Plastic, smooth, can be molded into rods without fracture, sticky when wet >50mm ~40% or more What is the texture classification for your soil sample?

D. State Soil Types Visit the following website to learn more about the state soils in United States: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=stelprdb1236841 Select four state soils, and explore them further by clicking on the Factsheet. Fill in information about each state soil below. Soil #1 State Name: State Soil Name: How many distinct layers can you see in the profile? What is (are) the dominant color(s) of the soil (i.e. dark brown, red, yellow)? When did this soil series become the state soil? Is this state soil well suited for agriculture? If yes, what kind? Describe one cool fact that you learned about this soil from the Factsheet: Soil #2 State Name: State Soil Name: How many distinct layers can you see in the profile? What is (are) the dominant color(s) of the soil (i.e. dark brown, red, yellow)? When did this soil series become the state soil? Is this state soil well suited for agriculture? If yes, what kind?

Final Questions 1. Based on the texture of your soil sample, would you expect water to infiltrate well or poorly in your soil? Explain. 2. What does the color of the soil sample suggest about the fertility of your soil? 3. What does the depth of the O and A horizons suggest about the fertility of your soil? 4. What amendments (i.e. fertilizer, compost, peat moss, etc.) would be needed to make your soil sample optimal for agriculture? 5. Did your soil sample look at all like the Maryland State soil? Why or why not?