Transcript Chapter 18
Soil Conservation Erosion • Two billion tons of U.S. soil lost annually • Improved from Five billion tons in 1982 • Conservation programs and voluntary conservation tillage practices • Tolerable losses (rule of thumb) at most – • One to five tons/acre annually • Missouri 4.1 tons/acre (2003 data) Erosion • Damage may be On-site or Off-site • On-site damage includes: • • • • • Topsoil losses O.M. and nutrients Decreased root zone Decreased Plant Available Water Gullies - make equipment operation difficult Erosion • Off-site damage includes: • Pollution of lakes and streams (nutrients and pesticides carried with eroded soil) • Sediment filling in lakes and reservoirs Erosion • Cost of Erosion • Two separate costs » Costs to the farmer and consumer (production loss) » Costs to the public (pollution and sedimentation) How Water Erosion Occurs • Three steps: • 1) raindrop impact shatters aggregates • Loosened particles seal soil voids limiting infiltration • Moving water also removes particles • 2) detached grains move in flowing water • 3) soil is deposited when water slows down How Water Erosion Occurs • Erosion (a form of work) takes energy • Energy comes from falling raindrops or moving water • Energy relates to size of drop and velocity • High energy can remove more and larger particles affecting amount carried off field • Deposition occurs when energy of running water decreases Four Erosion Factors • • • • Texture and Structure Slope Soil cover Roughness of soil surface Four Erosion Factors • Texture and Structure • Texture has two effects – Influences infiltration rate – Particle size affects ease of detachment » Silt particles are most easily detached • Structure also influences infiltration – Granules reduce runoff – Strong peds resist impact of raindrops – O.M. content aids in good structure formation Four Erosion Factors • Slope: • Two components • Length • Grade • Long, gentle slopes can have the same erosive potential as short, steep slopes – see figure 18-6, p. 300 Four Erosion Factors • Surface Roughness – Rough surface slows velocity – Depends on tillage practices • Conventional tillage – smooth • Chisel plowing - rough Four Erosion Factors • Soil cover – Reduces energy available to cause erosion • Mulch • Cover of crop – e.g. turf or hay reduces energy plus plant roots hold soil • Row crops or nursery have varying effects depending on planting distances and stage of growth (canopy increases with growth) Types of Water Erosion Listing by Increasing Severity • • • • • Splash erosion Sheet erosion Rill erosion Ephemeral gullies Gully erosion • Severity limits workability; e.g. gullies can’t be crossed by equipment Predicting Soil Loss: The USLE and RUSLE • Universal Soil Loss Equation • Main tool for estimating erosion rates • Predicts only sheet and rill erosion