Overview: This lesson will help students gain an understanding of the relationship between organic matter in the soil and water holding capacity. Normal field soil water- holding capacity is 60-80% of its total capacity; that is 60-80% of the water filled pore spaces are filled. This corresponds to the optimal biological activity of 60-80% of the water-holding capacity. When the water-holding capacity falls below 55-60%, organisms could suffer from dryness; and when the capacity is over 80%, they begin to suffer from a depletion of soil oxygen.
Grade Level: 6-9.
Connection to the Curriculum: This lesson is to be used in conjunction with a soil ecology unit that explores all aspects of soil use.
Time Required: The total time required including class discussion and follow up will be approximately two days.
Materials and Equipment: Soil samples (oven dried), Humid Chamber, Hilgard soil cups, Drying oven, Spatulas, Mortar and pestle, Triple beam balance, Filter paper.
Objectives: The student will complete a hands-on activity that will allow them to determine the water-holding capacity of soil. Each student will use the process of observation, classifying, exploring, recording, predicting, inferring, investigating, and valuing.
Body of Presentation: This will work well with any lesson on soil and water capacity or use. It works well with previous soil lessons that may have required the drying of soils for other experiments. This will allow the students to use other predried samples from previous experiments rather than dry samples for this one particular exercise.
Assessment: This will be accomplished by the students completing a correct data information sheet used during the course of this experiment.
Lesson Extension: This lesson can be extended by using other soil types. Soils used for comparison can range from those in cities, construction sites, grasslands, and fields in and out of production. Charts can be used to compare various soils for water holding capacity.
Soil A Soil B Weight of dry cup with wet filter _______________ _______________ Weight of dry cup and dry soil _______________ _______________ Gross weight (same as above) _______________ _______________ Dry soil weight _______________ _______________ Saturated soil and cup weight _______________ _______________ Minus weight of cup _______________ _______________ Weight of wet soil after drained _______________ _______________ Minus weight of dry soil _______________ _______________ Water (g) _______________ _______________ % Water holding capacity _______________ _______________