Erosion and Soil Degradation

Soil forms slowly, often less than a millimeter a year, as rock weathers and organic matter builds up. Erosion removes it fast whenever soil sits exposed. Wind picks up loose, dry particles and carries them off; rain detaches particles and washes them downslope before they can soak in. Plant roots are what normally stop this: they physically lock soil grains together and their canopies break the force of wind and falling rain before it hits bare ground. Strip the plants away, through plowing, overgrazing, or clearing, and the same wind or rainstorm that the soil used to shrug off now carries it away.

Farmers fight erosion by changing how a field handles wind and water rather than by resisting them head-on. Contour plowing follows the curves of a hillside instead of running furrows straight downhill, so each ridge acts as a small dam that slows runoff. Terracing cuts a slope into flat steps, turning one long fast fall of water into several short, gentle ones. Windbreaks are rows of trees or shrubs planted to slow wind at ground level, so it can no longer lift dry topsoil. Each method targets a different force, water flowing downhill or wind moving across the surface, but all three work by keeping soil in contact with something that holds it.

This matters beyond the field itself. A watershed connects every slope to the streams below it, so soil stripped from upstream fields does not just disappear. It washes into rivers, clouding water, smothering fish habitat, and filling reservoirs with sediment, linking soil degradation directly to the water systems covered alongside it in this unit.