APES Soil Science Labs
Objective: To investigate the physical, chemical and biological properties of soils
Overview: You may work with a partner or in a group of three to complete a series of laboratory investigations to determine the physical, chemical and biological characteristics of your chosen soil. Each lab must be written up according to the guidelines for writing a science lab report at Roosevelt High school. You may choose to write all the reports as a group or designate group members responsible for specific reports. Each student should retain a copy of every lab for their notes.
You are expected to use Chapt. 9 of your textbook, the soil formation and properties background information handout and any other resources you find useful, to write an appropriate background and discussion section for each lab in your own words. Remember to use the rubric to guide your lab write up.
The labs are as follows:
1. The physical and chemical weathering of rocks
2. Soil texture, structure and color (texture must be conducted using texture by feel and particle size analysis)
3. Soil permeability and density
4. Soil nutrients and pH (see test kits for procedure)
5. Soil mesofauna extraction
Each lab is worth 25 points and will be graded according to the standardized rubric for Roosevelt Science Dept. lab reports.
All labs are due by the end of the unit.
Soil Texture, Structure and Color Lab
Soil texture by Feel
Procedure: In this activity you will use the “texture by feel” analysis of soil flow chart to determine the texture of your unknown soil sample. First, familiarize yourself with the procedure by practicing the soil analysis using the known samples, sand and clay. Then determine the texture of the unknown.
During the known sample analysis, sand should not form a ball even after water is added. Use the clay sample to practice forming a ribbon. Clay should form a ribbon that is at least 5cm long before it breaks. If you have trouble getting a 5 cm ribbon, make sure the ribbon is of uniform thickness and width. Practice with the clay until you can confidently make a ribbon. Then use this technique to determine the texture of your soil.
Record your results on your own paper.
Soil Texture by Fractionation
Sand is larger and so will settle out faster in a suspension. Silt is the next size, so it will settle next. Clay is the smallest so it will settle on top.
Procedure:
Day one: Fill a graduated cylinder to 25ml with your soil sample. Add water up to the 75ml line. Cover with film and invert several times to make sure sample is in suspension. Leave it to settle.
Day two: Observe three distinct layers. Measure the volume of each layer and the total volume of the sample. Calculate the percentage of each component.
Amount of each component / total vol. of soil X 100 = %component
Record your results. Use the “soil textural triangle” to identify your soil texture.
Compare your results to the results obtained by texture by feel analysis.
Soil Structure
Procedure: compare your soil structure to the pictures provided. Identify your soil as granular, blocky or platy. Then define the size of the aggregates. If it appears not to have any structure it may be described as single grained or massive.
Soil Color
Procedure: This is typically conducted in the field as soil moisture content will affect color. Soil scientists grade soil samples with a munsell color chart by matching three distinct categories:
Chroma – the purity of the color
Hue – the dominant rainbow colors (red, yellow, blue and green)
Value – the relative darkness of the color (how much light is reflected)
Match your sample to the munsell color chart and record your results.
Soil Permeability
Objective: To compare the permeability of your collected soil sample to known samples of sand and clay.
Procedure: Work as teams of three so each person can monitor one of the three cylinders. Line each of the three filter funnels with filter paper and place on top of a 50ml or larger graduated cylinder. Fill each funnel with 15 grams of sample. Pour 40mls of water into each funnel and record the amount of water drained into the cylinder every 30 seconds for up to 5 minutes.
Note: You will want to create an appropriate results table before you start this lab
Questions:
1. Which sample drained fastest? Which was slowest?
2. What can this data tell you about the movement of nutrients and pollutants through each soil type?
3. Prairie soils, such as those found in much of Iowa, have a relatively low clay content. What can you infer about the movement of water, minerals and pollutants through such soils?
Soil Bulk Density
Objective: To determine the bulk density of your own soil sample relative to the density of sand, clay and humus.
Dense soils have high strength, low porosity, and poor plant growth. Soils can become more dense due to compaction resulting from machinery or high traffic.
Procedure: Weigh out 15 grams of sand. Pour into a dry 100ml cylinder. Tap gently on the table to settle the sand. Determine the volume in the cylinder and record your result. Calculate the bulk density (Density = mass/volume) remember your units! Repeat this procedure for the clay sample, humus and your own soil. Present your results in a table.
Questions:
1. Compare the bulk densities of soils with different particle size distributions and different textures. Is there any correlation between particle size, texture and bulk density?