Soil Bulk Density Teacher Instructions Introduction: This protocol allows students to determine the bulk density of soil in several locations. The bulk density is one way to look at soil health. You will need access to a drying oven or toaster oven. This lab works best when combined with the other soil labs ie Soil Compaction, Soil Food Webs etc. Also, remind students to wear clothing suitable for outdoor work. Objectives: 1) Determine the bulk density of soil. 2) Determine the structure of the soil. 3) Hypothesize what type of biota may live in that soil. Students Required: Groups of four. Estimated Time: 3 class periods (depending on nearness to sample site). (Day one 40 minutes, days two and three 50 minutes each) Overview of Tasks: Day One(40 minutes): 1) Break the students into groups of four. 2) Have the students read the student instructions together as a group. 3) Have the students assign the following roles: a) Researcher – student is responsible for conducting the protocol. b) Recorder – student is responsible for recording all data in his/her journal. c) Reporter – student is responsible for compiling the data to be used in the written report. d) Assistant – student is responsible for helping any of the other students. 4) Have the students record any initial questions or ideas about the task in their journal. 5) Conduct a class discussion about these questions or concerns. 6) Assign soil sites to each group. 7) Have students prepare trash bags and sand buckets. 8) Have students label their sample bags before going to the field. Day Two (50 minutes): 1) Go to the field. 2) Allow students to conduct student instructions. 3 Come back to class. 4) Have the students begin drying the soil. *Remember that the soil should be dried overnight. 13) Debrief the day’s work.

Day Three (50 minutes): 1) Review the experiment. 2) Allow students to continue through student instructions. *Monitor the removal of drying pans to prevent student injury 3) Debrief the student instructions. 4) Have the students interpret results and discuss. 5) Allow students to write a lab report and share findings with the class.

Soil Bulk Density Student Instructions Introduction: The number and variety of plants and soil organisms found in a forest are affected by the density of the soil (remember: density = mass/volume, measured in g/mL). Soil “bulk density” (dry weight of soil /volume) depends on several factors including the following: Density of the mineral soil particles, amount of organic matter, compaction of the soil, activities of burrowing soil animals such as earthworms, and the abundance of plant roots. Bulk density for a soil is often used as a measure of soil structure. A lower density generally means greater porosity and larger soil aggregates. A healthier forest soil will have a lower density, which corresponds to greater stability, less compaction, and probably greater moisture content than a soil with a higher density. A simple method for measuring soil density is to dig a hole, keeping all the soil removed from the hole as a sample, determine the volume of the soil sample by pouring a volume of dry sand into the hole from which the sample was removed. Finally, dry the removed soil sample to determine the dry weight of the soil.

Materials: Small Aluminum tins Tall kitchen trash bags Plastic containers with lids, such as liter bottles for moving sand Sand (3L) Drying oven Ziploc baggies Balance

Procedure: Each group will follow these procedures. You will aggregate your results. Day 1 (40 minutes): 1. Break up into groups of four 2. Each group should assign to the following roles to individual group members: a. Researcher – student is responsible for conducting the student instructions. b. Recorder – student is responsible for recording all data in his/her journal. c. Reporter – student is responsible for compiling the data to be used in the written report. d. Assistant – student is responsible for helping any of the other students. 3. Read all of the student instructions. 4. Select the soil sampling sites for each group.

5. Prepare Trash Bags: 1) Cut the kitchen bags into 50cm x 50cm squares - you will need at least 3 squares. 2) Fill containers with sand. 3) Determine Sample Site 4) Label baggies to reflect the sample location. Day 2 (50 minutes, note travel times will vary): In the Field 1) Go to the sample site. 2) Record any observations about the site, like: water content, type of plants around, development etc. 3) Clear the soil of litter and the O horizon. 4) Use a spade or trowel to dig a small hole about 10cm deep and 10cm in diameter. Make certain that all the contents of the hole are transferred to an appropriately labeled Ziploc bag. The sides of the hole should be as smooth as possible. Do not remove rocks from the sample, as they are included in the bulk density measurement. 5) Line the hole with the square piece of plastic. 6) Pour sand into the hole until the surface of the sand is flush with the top of the soil. 7) Carefully remove the plastic liner with the sand. Be careful not to lose any sand, as this will help determine the soil density. Put the sand and the liner into another baggie. Back at the Classroom 8) Return to the classroom. 9) Mass and record each soil sample while still in the Ziploc bag. 10) Label enough tins to place each sample in its own container. 11) Mass each empty tin and record this in your data table. 12) Place each soil sample into a labeled tin. 13) Allow the samples to dry overnight in a drying oven at a low temperature o

(100 F). 14) Carefully remove the sand that filled the hole from the sample bag, and place it in a large graduated cylinder (100 mL or 250 mL). 15) Record the volume of sand. (This is the volume of the soil sample).

Day 3 (50 minutes): 1) After the soil has dried, obtain the dry mass. 2) Subtract the mass of the tin from the mass of the dry soil. 3) Calculate the bulk density of the soil by dividing the dry mass of soil by the volume of the sand. 4) Record all your results

5) Each group should share their findings/data with the class. This should include a site description. 6) Interpret results and discuss findings. The following questions are designed to help you make meaningful conclusions. a. Which site had the highest soil bulk density? Which had the smallest? b. How would you describe the distribution of different densities of soil across your sire? c. What do you think was the cause of the variation in density at your site or when you compared two or more sites?

Soil Bulk Density Sample Data Sheet

Sample Site: Sample Number

Moist Soil Mass

Mass of Tin

Dry Soil Mass

Calculations: (Dry soil mass - Mass of tin)/Volume of sand

Volume of Sand

Soil Bulk Density