U.S. DEPARTMENT OF THE INTERIORBUREAU OF LAND MANAGEMENT

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### SLOPE ASPECT AND SOIL TEMPERATURE

Objective: Students will determine the effect of aspect (the direction faced by the slopes that contain crops) on soil temperature.

Materials: For this activity, you will need

• two empty half-gallon milk cartons,
• two laboratory thermometers,
• enough soil to fill both cartons,
• dark-colored construction paper,
• scissors,
• and graph paper.

Procedure: To construct the model, first cut away a side from one of the milk cartons, and staple or tape closed the top portion where the carton opens. Then, cut a rectangle of construction paper that measures the length of the carton and twice its width. Place the paper rectangle inside the carton so that half of it still extends above the side. Fill the carton with soil, which will hold the paper in place. Prepare the second carton in the same manner.

Find a window sill on which the two samples will fit with room to spare. They must also be easily accessible to students. Face one carton directly toward the outside, tilting it slightly to simulate a south-facing slope. The construction paper should be opposite to the side facing the window. Place the other carton in the window so that it faces away from the outside (construction paper toward the window), simulating a north-facing slope. Tilt the carton a bit.

Locate the center of each carton and push the thermometers into the soil about 5 cm. When the mercury in the thermometers stabilizes, record the temperature. Remove the thermometers after each reading.

Continue to check and record the temperatures throughout the day. Compile a log of times and temperatures, and then graph the data. You might run this experiment for a single class period, for one day, for a season, or for an entire school year.

The carton facing the outside will show temperature readings significantly higher than will the inward-facing carton. As well, the soil from the simulated south-facing slope will retain heat longer.

Discuss the results with your class. What was the greatest difference in temperature between the two cartons? What was the least difference? When did those readings occur? Was there a difference in how quickly the soil samples heated up or cooled down between readings? How does slope aspect affect soil temperature? How might your conclusions apply to the people of the Hupobi and their dry-farming techniques? (The ancient inhabitants of the Hupobi planted those crops requiring higher temperatures and a longer growing season (such as maize) on south-facing slopes. Crops that grow for a shorter period and in cooler temperatures (such as squash) were planted on the other slopes.)

This lesson was developed by Terrill L. Nickerson, the Santa Fe Indian School.

Last updated: 11-13-2009