Why might soil weather and erode? There are a number of factors… 1. Climate 2. Vegetation 3. Topography 4. Parent Material 5. Time 6. Human Activities

How does climate cause soil erosion?

Energy and precipitation strongly influence physical and chemical reactions on parent material in the soil. Climate also determines vegetation cover, which in turn influences soil development. Precipitation also affects horizon development factors like the translocation of dissolved ions through the soil. How does hot dry climates impact the soil?

Hot, dry desert regions- sparse vegetation and hence limited organic material available for the soil. Lack of precipitation inhibits chemical weathering leading to coarse textured soil in arid (dry) regions. In cold regions- bacterial activity is limited. In the warm and wet tropics- bacterial activity proceeds at a rapid rate, thoroughly decomposing leaf litter. (Tress take up the nutrients from the soil, and high rain fall flushes away some organic material in the soil). As a result the upper horizons (layers) of the soil lack organic matter.

Vegetation's role in impacting soil… Pine forests- Decomposing pine needles in the presence of water creates a weak acid that strips soluble bases from the soil leaving it in an acidic state. pine trees have low nutrient demands so few soil nutrients are taken back up by the trees to be later recycled by decaying needle litter. Deciduous forests- Broadleaf deciduous trees like oak and maple have higher nutrient demand and thus continually recycle soil nutrients keeping soils high in soluble bases.

How might topography affect soil?

Water moving across the surface strips parent material away impeding soil development. Water erosion is more effective on steeper, unvegetated slopes. The amount and velocity of water, and rate of erosion increases as you near the base of the slope. (Parent material is striped away and can’t develop into a soil).

Soil parent material is the material that soil develops from. Which of the following is more prone to weathering? Soils developed on parent material that is coarse grained and composed of minerals. Soils developed on parent material that is fine grained unstable minerals.

Parent material composition has a direct impact on soil chemistry and fertility: Parent materials rich in soluble ions -calcium, magnesium, potassium, and sodium, are easily dissolved in water and made available to plants. Limestone and basaltic lava- both have a high content of soluble bases and produce fertile soil in humid climates. Parent materials low in soluble ion- water moving through the soil removes the bases and substitutes them with hydrogen ions making the soil acidic and unsuitable for agriculture. Soils developed over sandstone- are low in soluble bases and coarse in texture which facilitates leaching (the loss of water-soluble plant nutrients from the soil due to rain).

Time: As time passes, the weathering processes continue to act on soil parent material to break it down and decompose it. Horizon development processes continue to differentiate layers in the soil profile by their physical and chemical properties. older more mature soils have well-developed sequence of horizons. Some geological processes keep soils from developing by constantly altering the surface and not allowing parent material to weather over a significant period of time. (ex: Hillside erosion, river deposition of sediment).

Organism, both plant and animal, play an important role in the development and composition of soil. Biotic elements of the environment need life-sustaining nutrients that find their origin in the soil. Upon their death, organisms return these nutrients to the soil to be taken up again by other plants and animals. This cycling refreshes and maintains the nutrient status of soils (this enables soils to support life). What types of trees contribute little nutrients to the forest floor?