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.