Lecture 1 - Intro to soils

Question 1

What is soil

Answer 1

the layer of unconsolidated material on the Earth’s surface that serves as a natural medium for plant growth

Question 2

importance of soils

Answer 2

• releases nutrients required for life in waterways and for land animals (ag)
• store water for plants
• improve water quality
• recycle nutrients and carbon -> nutrient cycles
• recycle wastes -> decomp
• food
• physical support for building and construction

Question 3

function of voids

Answer 3

• allow space for root growth deep into the soil
• provide water storage
• store carbon and air for plant growth – aeration of roots

Question 4

major components of soils

Answer 4

• mineral (45%)
• OM (1-5%)
• air (25%)
• water (25%)
• soil organisms – billions

Question 5

How do soils support plants

Answer 5

• physically
• aeration of roots
• water storage
• thermal insulation
• control toxicity (filtration + pH)
• nutrient supply (recycle)

Question 6

how is Australian soil difficult?

Answer 6

• slow formation (~ 300 years per cm)
• nutritionally impoverished, structurally challenging, salty, N2 and P deficiency
• infertile and mostly sandy loams

Question 7

what factors impact soil formation

Answer 7

• parental material, climate (precip and temp), macro and microorganisms, topography (elevation, slope, position), time

Question 8

process of soil formation

Answer 8

1. weathering of top layer (lichens etc)
2. water movement into the soil
3. cracking and voids occur
4. roots able to penertrate soils

Question 9

how do soils change compared to parent material

Answer 9

• ## physically, biologically, chemically and structurally

Question 10

what is WA soils parental material?

Answer 10

• major rock types contains quartz, orthoclase, plagioclase
• Most of Australia is covered in a deeply weathered regolith which is covered in resistant duricrust (major parent material in Aus)

Question 11

define soil profiling

Answer 11

recording of morphological properties for each horizon recognised

Question 12

What are the different ways to describe a soil

Answer 12

• horizons (depths and thickness)
• texture
• pedality (ped shape, size, stability, abundance)
• colour (when wet)
• roots
• mottles (two different colours of soil next to each other)
• coarse fragments
• segregations
• moisture status
• pans (dense layer, might stop roots growing if hard)

Question 13

what are the soil horizons in a profile and how to ID

Answer 13

1. topsoil/Horizon A (top and high OM) - usually darker
2. subsoil/ Horizon B – different composition (lighter), materials leached from A, more clay (leached)
3. Parental material/ partially weathered rock (roots unlikely to penetrate -> rock or partly decomposed sand/clay
4. • very slightly weathered area (no roots)

Question 14

what is soil fertility?

Answer 14

• ability to support plant growth