Academic journal article The Science Teacher

The Resource beneath Our Feet: Gaining a New Awareness during the International Year of Soils

Academic journal article The Science Teacher

The Resource beneath Our Feet: Gaining a New Awareness during the International Year of Soils

Article excerpt

We purchase small bags of soil for our household plants and till our yards to develop gardens. We plow, cultivate, trample, contaminate, and remove soil. Our food, clothing, and ecosystems closely intertwine with soil, and yet we seldom notice or appreciate it.

Though soils continue to develop and mature, we degrade and destroy soil at an increasing rate (Amundson et al. 2015). By one estimate, erosion, nutrient depletion, acidification, salinization, compaction, and chemical pollution have moderately to highly degraded 33% of soil worldwide (FAO 2015b).

To increase public awareness of the importance of soil, the United Nations General Assembly designated 2015 as the International Year of Soils (IYS). One objective is to educate people about the crucial role of soils in food security, climate change adaptation and mitigation, essential ecosystem services, poverty alleviation, and sustainable development (FAO 2015a).

This article describes activities in which students sample, investigate, classify, and compare characteristics (i.e., texture, color, density, porosity) of local soils, evaluating whether the soils are healthy or at risk. Students investigate correlations between geology and geography, predict which soil types may go extinct in their state, and analyze how this will affect people.

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A soil primer

Soil, an accumulation of weathering products on the Earth's surface, is part of the pedosphere, which interacts with the atmosphere, lithosphere, hydrosphere, and biosphere. It can include varying amounts of organic material (e.g., humus) and pieces of broken rock. During weathering and erosion, exposed rock can break down to smaller particles. Physical weathering processes include frost wedging, pressure release (to create exfoliation domes), and the mechanical breakdown of rocks through biological activity (e.g., growing tree roots, burrowing animals). Rocks can also weather chemically, resulting in smaller particles of a different composition. Chemical weathering processes include dissolution, oxidation, and hydrolysis.

Soils are not homogeneous, and a layered soil profile develops over time (Figure 1). A typical soil profile has four main zones or horizons:

* O: build-up of organics, humus;

* A: zone of leaching, intense biological activity, topsoil;

* B: zone of accumulation, ores, subsoil; and

* C: partially disintegrated bedrock.

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Soil horizons (layers) can evolve and vary in thickness. Figure 2 illustrates how soil quality in Montana changed through agriculture, urbanization, and restoration.

Rock type and size (i.e., sand, silt, clay), climate, and topography affect soil formation--leading to many variations of soil horizons. These many types of soils constitute an area's pedodiversity (i.e., the variations of soil properties and classes). The United States categorizes over 13,000 soil series (Tennesen 2014), which the U.S. Department of Agriculture's Soil Taxonomy classifies according to 12 soil orders (Figure 3). Information, pictures, and global distributions of the orders are available online (see "On the web").

Soils in the classroom

In the activities described below, students investigate local soils that are relevant to them (Clary and Wandersee 2006) to identify characteristics and classify the soils via texture, color, density, and porosity.

Collecting soils

The following tips for classroom soil sampling come from Bigham (2010) and Taylor and Graves (2010). Before collection, teachers should determine how much soil is needed from each collection site, based on the classroom soil activities that will follow.

Use agricultural areas and undisturbed natural areas for sample sites. Soil types can vary within a relatively short distance (e.g., the soil atop a natural levee differs from the soil on the slope), so collect several soil samples at a site to document soil diversity. …

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