Group Members: Paul, Ian, Jisha
Purpose
For this lab exercise you are taking on the role of a soil scientist. Soil scientists receive samples of soil from individuals in the community and it is your role to analyze the soil sample that you have been given to make a recommendation to the homeowner about the quality of their soil and what they can do to improve the fertility of the soil. You will determine the quality of the soil through physical, chemical, and biological testing.
Materials
- Trowel
- Soil cup
- Graduated cylinder
- Spray bottle
- Sheet of yellow paper
- Soil test kit
- Small container for organisms
Procedures
Physical Testing:
- First take your spade/trowel and dig a square into the ground. Place your removed soil in the soil cup. Once the soil is removed, look at the walls of your hole and identify any layers and differences in color that indicates your soil profile. Sketch a picture in your lab notebook.
- Look at your soil sample and observe and comment on the various particle sizes.
- Next, take 25 grams to determine what type of soil you have
- To determine what type of soil you have, use the following chart:
5. Fill a graduated cylinder with 25 mL of your soil sample
6. Add water until there is about 50 mL in the cylinder
7. Cover the cylinder with a film and invert several times until the soil thoroughly suspended in the water. Place the cylinder on the counter for at least 30 minutes.
8. When the soil has settled out, there should be 3 distinct layers. Measure the volume of each layer
9. Calculate the percentage of each component
6. Add water until there is about 50 mL in the cylinder
7. Cover the cylinder with a film and invert several times until the soil thoroughly suspended in the water. Place the cylinder on the counter for at least 30 minutes.
8. When the soil has settled out, there should be 3 distinct layers. Measure the volume of each layer
9. Calculate the percentage of each component
Chemical Testing
- There are four variables that are important in determining the fertility of soils. They are pH, amount of nitrogen, phosphorous, and potassium. Use the soil test kit to determine the values of each variable - follow directions provided on the kit itself
Biological Testing
- Spread out a sheet of yellow paper and empty the rest of your soil onto it.
- Look for small creatures in the soil. If you find a creature, place it in a small container
- Determine what each creature is based on the reference chart
- Keep a count of each different type of creature you discover and the number of organisms within a species
- Create a bar graph to represent the number of each organism and the overall diversity of the soil
Observations
- soil ranges from big chunks to powdery grains
- layers are different shades of brown
- Color: 5 yr 4/4
Data
Soil Triangle: Silt Loam
Biological Testing: Soil Biodiversity
- Wireworm
- Woodlouse (2 organisms)
- Ant (5 organisms)
- Millipede
Analysis
- Humus plays a vital role in soil fertility because it promotes plant growth. It provides plants with their needed nutrition and minerals. Also humus contains organisms that break down plant waste and help roots absorb the nutrients.
- A healthy layer of topsoil is moist, crumbly, and full of chunks of dirt and plant material. Depending on the location, topsoil could be acidic or alkaline; it could also have a greater composition of clay or silt. Topsoil is being lost at alarming rates due to high rates of topsoil erosion; this erosion is primarily a result of human activities such as over-farming. Water runoff also causes loss of topsoil; plant life is severely affected by this. One way to prevent further topsoil erosion is to increase vegetation; plants and trees protect the soil with their meandering roots. Another way to stop further erosion is to adopt farming practices that do not have water runoff, which will help maintain the integrity of the soil structure.
- The layers in a soil profile are called horizons. The O horizon is the topmost horizon and contains humus, which is ever so beneficial to plants. The next is the A horizon, or the topsoil, which is dark and contain humus and others minerals; this is the horizons where seeds sprout and roots grow. This is the E horizon; it is light and has mostly sand and silt. It leaches most minerals and clay as water drips through. The B horizon is the subsoil and has clay and mineral deposits leeched from above layers. Next, the C horizon has partially broken-up rock; roots do not grow in this layer. The last horizon is the R horizon, which is solid rock. This soil profile is likely to be found in a coniferous forest biome found in the North Caroline Piedmont region.
- pH is a very important aspect of soil fertility. It is important because it influences how easily plants can take up nutrients from the soil. For example, plants are able to absorb phosphorus when the pH of the soil is between 6.0 and 7.0.
- There are many natural sources of nitrogen, potassium, and phosphorus found in soil. Nitrogen is replenished in the soil after each harvest when plant matter and decaying plan matter is turned into humus. Phosphorus is produced by bacteria in the soil. Sources of potassium in the soil include dead plant material, manure, and compost.
- The form of nitrogen in the atmosphere, is unusable by plants because it is nonreactive; the process which atmospheric nitrogen is converted into a form that plants can readily absorb through their roots is called the nitrogen fixation. In order for plants to use nitrogen, it needs to be converted into a nitrate compound in the soil by nitrogen-fixing bacteria.
- The three primary plant nutrients, nitrogen, potassium, and phosphorus and used by living organisms in a plethora of ways. Living organisms use nitrogen to produce complex organic molecules. Phosphorus is necessary for nucleic acids and ATP and plays a big part in the nervous and circulatory systems. Potassium helps increase crop yields an aids in water absorption.
- According the results of this lab activity, the fertility of the soil is “bad.” There is a sufficient amount of potassium. But there is a deficiency in phosphorous and nitrogen is depleted. A deficiency in phosphorous causes small, frail plants with reddish leaves and a depletion in nitrogen will cause yellow leaves.
- A silt loam with a pH of 7.5 best supports grasses; the location had a few plants growing around it and had grasses growing.
- There was also an abundance of biological diversity present in the soil sample studied, which may indicate that the soil has nutrients. The biodiversity of the soil used in this lab activity is greater than that of other nearby locations. This is due to the fact that our location was surrounded by an abundance of producers who are the bases for food webs. One factor that may have impacted the amount of biodiversity for the soil studied is the moisture in the soil. Other factors, such as the nutrients in the soil and the surrounding temperature also determine the biodiversity in the soil.
- Some possible sources or error in this experiment are not digging the square to the specified depth, misreading the chemical tests, and missing some organisms living in the soil. Not digging the square to the specified depth would result in a different layer or horizon of soil studied. Misreading the chemical tests would mean that the amounts of measured nutrients in the soil are wrong, and lastly, missing some organisms living in the soil would lead to a lower biodiversity in the results.