Notes
Soil
- Soil forms slowly from weathered parent material and organic matter (humus). It contains sand, silt, clay, water, and air. Loam is balanced and ideal for farming.
- Horizons: O (organic litter), A (topsoil), E (leaching), B (subsoil), C (weathered parent material), R (bedrock).
- Leaching moves minerals downward. Soil pH controls nutrient availability.
Agriculture and erosion
- Monoculture is efficient but risky. Sustainable practices include crop rotation, cover crops, no-till, contour plowing, terracing, windbreaks, and integrated pest management.
- Irrigation can cause salinization. Overgrazing can cause desertification.
- Erosion removes topsoil; the 1930s Dust Bowl resulted from drought and plowing of prairie grasses.
Forests and cities
- Deforestation (ranching, crops, logging) destroys habitat, increases erosion, and releases $CO_2$. Use selective cutting, reforestation, and sustainable forestry.
- Urban sprawl converts land and increases impervious surfaces, runoff, and car use. The urban heat island makes cities warmer. Smart growth limits these effects.
Topics in this unit
Each topic has its own short notes and practice.
Practice
The A horizon, or topsoil, is rich in organic matter and living things.
Plowing along the contour slows water and reduces erosion.
Controlling evaporation and flushing salts reduces buildup.
Impervious surfaces send rain to storm drains instead of the soil.
Most nutrients were held in the vegetation, not the soil.
Sand has large pores that let water pass through quickly.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A farmer owns a steep hillside field planted with corn every year. After several heavy rains, the farmer notices gullies forming and muddy water running into a nearby stream.
(a) Identify the environmental problem occurring in the field and one cause.
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The problem is soil erosion (loss of topsoil). Causes include steep slope, plowing up and down the hill, and bare soil with little plant cover between crops.
Check off the points you earned:
(b) Describe two conservation practices that would reduce this problem.
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Contour plowing and terracing slow runoff on slopes. Cover crops or no-till farming keep roots and residue in the soil so water and wind cannot carry it away easily.
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(c) Explain one effect of the muddy runoff on the nearby stream.
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Sediment makes water cloudy, blocking sunlight from aquatic plants, and can smother fish eggs and clog gills. Fertilizer attached to soil can also add nutrients that cause algal blooms.
Check off the points you earned: