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