Soil: Formation, Composition & Conservation

Key Chemical Processes

  • Oxidation (e.g., rust)

  • Carbonic acid from CO<em>2CO<em>2 + H</em>2OH</em>2O

  • Acid rain (from SO<em>2SO<em>2, NO</em>xNO</em>x)

Humus & Detritus

  • Humus: dark, nutrient-rich organic fraction; holds moisture

  • Detritus: eroded mineral/organic debris, fuel for detritus food chain

Human Impacts (Keystone Species)

  • Dust Bowl: drought + poor tillage + wind erosion

  • Midwest loss: 57.657.6 billion t topsoil in 160160 yrs; erosion ≈ 1.9 mm/yr1.9\,\text{mm/yr}

  • Topsoil formation rate ≈ 1 inch1\,\text{inch} per 10001000 yrs

Soil Conservation Strategies

  • No-till / low-till: could cut erosion ≈95%\approx95\% in 100100 yrs

  • Contour strip cropping, residue cover, cover crops

  • Benefits: less erosion, higher water retention, lower CO2CO_2 release, reduced fuel use

Special Soil Systems

  • Dolomite prairies: high MgMg from weathered limestone → unique flora

  • Biological soil crusts: lichens, cyanobacteria etc.; stabilize ~12%12\% of land; fix CC, NN

Quick Facts & Figures

  • Topsoil depth (ag fields) ↓ 14 in14\,\text{in} relative to prairie

  • Potential yield loss when topsoil gone: 50!–!70%50!–!70\%

  • Shiprock (NM) shows differential weathering of volcanic neck vs. shale

Review Questions

  • Why is soil an interface?

  • What makes soil “alive”?

  • List soil components & their %.

  • Define weathering & its two main types.

  • Time to create 11 inch topsoil?

  • Could another Dust Bowl occur?