structure salinity sodicity

Question 1

soil structure controls

Answer 1

size and arrangement of pores

Question 2

soil structure is developed by 2 processes

Answer 2

physical and biological processes

Question 3

Soil structure controls 3 imp properties:

Answer 3

Permeability, pore size and soil strength

Question 4

Soil structural stability describes the…

Answer 4

ability of soil structure to be retained when stressed (e.g. wetting, traffic)

Question 5

Two processes that degrade soil structure

Answer 5

DIspersion and slaking

Question 6

Two ways to enhance structural stability

Answer 6

Increasee OM content, and add sources of Ca, especially gypsum and lime

Question 7

What changes to soil structure from poor structural stability, and can they be measured?

Answer 7

• generation of finger material on wetting
  +eg. slaking produces smaller aggregates
  + e.g. dispersion: colloids (dispersed clay)
  -decreaseed permeability
  +simple lab tests of hydraulic conductivity
• increased strength
  +penetrometer resistance

Question 8

Mechanisms that destroy soil structure

Answer 8

• Tillage
• Compaction
• Grazing
• Raindrop impact
• Slaking
• dispersion

Question 9

Slaking

Answer 9

Water moves into pores, rapid wetting, air has to go somewhere, starts pushing outwards. Increased water content causes swellling which reduces strength. Agg starts breaking down

Question 10

Dispersion

Answer 10

Na: Ca ratios. Clay platelets spread apart. Float around when wetting occurs

Question 11

Conserving soil structure. Maximise soil stability by:

Answer 11

• Avoid soil disturbance (minimum tillage, no traffice, reduce grazying, increase plant cover)
• Increase OM - plant residue rotation, more pasture, reduced tillage
• Calcium amendments (lime (CaCO3), gypsum (CaSO4, 2 H2O)

Question 12

Restoring soil structure

Answer 12

1. maximise plant and biological activity (plants, roots provide glue to stick aggs together)
2. OM/ Ca inputs