4: Soil Structure

Question 1

Soil structure

Answer 1

Defines how soil mineral particles (sand, silt and clay) are bound together and arranged in the three dimensional space

Question 2

Peds or aggregates

Answer 2

Are the structural units in soil formed by particles bound together

Question 3

Why is soil structure important?

Answer 3

Determines soil capacity to hold water and air

Provides habitat for microorganisms

Provides physical protection of organic matter/C sequestration

Question 4

Granular

Answer 4

A good, healthy soil structure
Aggregates look like “cookie crumbs”
Particles held together by organic substances

Question 5

Wedge

Answer 5

Elongated shape; polished surface (slickensides)
Caused by the shrink-swell process

Question 6

Platy

Answer 6

Thin, flat, horizontal plates
Compacted surface soils

Question 7

Blocky

Answer 7

Irregular blocks
1.5-5.0 cm in diameter
Particles held together by clay

Question 8

Prismatic

Answer 8

Vertical columns
Particles cemented by shrink/swell (smectitic) clay

Question 9

Columnar

Answer 9

Vertical columns with rounded tops

Question 10

Massive

Answer 10

Structureless
Have fine texture, essentially making them massive clumps

Question 11

Single grain

Answer 11

Mostly made of sand

Question 12

Balance between micro and macropores

Answer 12

Micropores hold water more tightly than macropores. Macropores and structure are critical for good drainage and aeration.

The balance between them determines if a soil drains well but also holds enough water