soil water 2

Question 1

• Interrill erosion

Answer 1

Lect 1 pg 7. In interril erosion, sheet erosion, detachment is occurring across whole area. Mechanism is rain splash. Interrill erosion is main form of water erosion, doesn’t form gullies, just rain splash movement of particles down slope. However, mass of particles moved is greater than rill (rill erosion is movement across the surface)

Question 2

erosivity

Answer 2

Is about the agent (erodibility is about the land and soil). About strength of wind and water as agent. Eg. Erositivity of rain – heavy rain = bigger drops which have faster terminal velocity

Question 3

USLE

Answer 3

Model to quantify and estimate soil loss as a product of different contributing factors. Erosivity, physical characteristics, slope etc

Question 4

Describe the operating principles (be specific) for two different instruments used to measure soil matric suction

Answer 4

• Ceramic Cup Tensiometer
  o Lecture comments: Air can’t move into porous ceramic cup. Porous ceramic cup at bottom, allows movement of soil solution but not air if wet. Cup has water filled pores. Ceramic cup starts out filled with water. Matric suctionsucks water out of pores in ceramic tip. Measure pressure of gas. Water pulled out of ceramic until that pressure equals suction of soil pores on the water in the ceramic connected to those soil pores
  o Specific slide info:
   Filled with air-free water, sealed, set to zero, placed in soil
   Measures matric suction (sucks water out of pores in ceramic tip) in range 0-85 kPa (lecture comment: will only work in range 10-1500 kPa – wet range of soil, won’t work at plant wilting point etc)
   Slow response time (depends on quality of vacuum-gauge & permeability of ceramic cup)
   Used to monitor water demand and to schedule irrigated row crops, glasshouses, and containers
• In drier regions need different technology: Gypsum block
  o Is a rectangular shaped cast of gypsum with bared copper wire electrodes embedded.
  o As gypsum dries out electrical resistance increases. When placed in direct contact with soil it comes into equilibrium with soil water potential, which can be related to electrical resistance
  o Basically, is porous material which forms an electric circuit, and the resistance of the circuit depends on the amount of water in the block

Question 5

In the context of the USLE, list and discuss 3 inherent soil properties that influence soil erodibility. PHYSICAL CHARACTERISTICS PART OF ERODIBILITY FLOW CHART
K depends on the OM, texture of the soil, its permeability and profile structure

Answer 5

• Texture
  o Fine, sandy and silty soil textures more erodible
   Small, light, and also soils that don’t bind
   Hard to influence texture
   (not really clays b/c they bind to things and so don’t erode quickly)
• Structural Stability
  o Slaking
  o Dispersion
• Structure
  o Hydraulic properties
  o Ie of whole soil profile. E.g. if sandy on top, and clay below. Water moves quickly in through sand. If sand becomes saturated, whats limiting movement downward is whats beneath it. If it can’t move down into the clay, starts pooling on the surface, increases potential for erosion
• Surface structure
  o Influences water retention of water
  o Again related to pooling, but if you make surface rougher, and make water stay on surface longer reducing run off

Question 6

clay content

Answer 6

: (shrinking and swelling – high clay content, strong aggs, won’t slake as much. With V sandy soils no aggs). Need clay to bind to microbial matter/ provide structure