Parent Material (Lecture 18)

Question 1

What is organic parent material?

Answer 1

peat (histosols)

Question 2

What is quartz rich parent material?

Answer 2

sandy soils (arenosols)

Question 3

What is volcanic parent material?

Answer 3

Allophanes (andosols)

Question 4

What are arenosols?

Answer 4

Sandy soils dominated by sand size fraction

Soils in almost pure quartz sands

Not very fertile

Important because they cover large area (in many diff. envr)
- are among the most extentive soils in the world, covering about 7% of surface
- From arid to human envr and from extremely cold to extremely hot
- occur on very sold surfaces as well as in very recent landforms, and may be associated with almost any type of vegetation

Question 5

What are the 3 categories of arenosols?

Answer 5

Residual sands as a result of prolonged weathering of quartz rich rocks

Aeolian sands as a result of deposition by wind

Alluvial sands as a result of transportation by water

Question 6

What are the characteristics of arenosols of the arid zone?

Answer 6

Develop on shifting sands and sand dunes

Minimal soil dev. also due to permanent wind erosion

Diverse mineralogical composition. Many contain gypsum or carbonates

Rich in bases (K, Mg, Ca) despite being dominated by quartz since it is not leached away due to very low precipitation (what is there remains there)

Question 7

What are the characteristics of arenosols of the temperate zone?

Answer 7

More pronounced soil formation than those of the arid zone due to higher precipitation rates

Occur on fluvio-glacial, alluvial, lacustrine, marine, or eolian sandy sediments

Often first signs of podzolation

Deeply decalcified due to substantial precipitation (calcium is leached out of soil profile)

Low contents of bases

Low CEC due to sandy texture

Question 8

What are the characteristics of arenosols of the humid tropics?

Answer 8

Either young soils on eolian or alluvial deposits

Or very sold soils that lost almost all minerals with the exception of coarse grained quartz

Usually Ah horizon with thick sandy B horizon (can be very deeply developed)

Question 9

What are arenosols’ water properties?

Answer 9

Very permeable for water with saturated water conductivity

Low water holding capacity

Rapid drainage –> water losses

Mineral fertilizer should be provided in many single doses to reduce leaching losses

Question 10

How do arenosols hold up to erosion?

Answer 10

Sensitive to wind erosion and compaction due to loose single grain soil structure

Question 11

Where are andosols found?

Answer 11

Cover only 0.84% of the ice-free land but host 10% of the world population –> provides food for huge number of organisms

Question 12

How are volcanic rocks/magma grouped? What are the 3 categories?

Answer 12

According to their silica contents

1) Rhyolite: 65-75% SiO2
2) Andesite: 55-65% SiO2
3) Basalt: 45-55% SiO2

Question 13

How does SiO2 content correlate to viscocity, acidity and explosivity of volcano?

Answer 13

The higher the silica content of magma, the more acid and viscous it is and the more explosive volcanic eruptions are

Hence, rhyolite has slower lava flow than basalt

Question 14

Aa

Answer 14

Rhyolite

When these lava flows cool, they create very rugged rock envr.
- rock material has very sharp edges

New soil dev. would begin more quickly than Pahoehoe since weathering will be more pronounced and easier for organisms to set root and colonize (more surface)

Question 15

Pahoehoe

Answer 15

Less rich in silica (flow more fluid)

Rope-like features

Question 16

What are the characteristics of volcanic soils?

Answer 16

Volcanic rocks contain volcanic glass that weathers easily

Soils that developed on volcanic materials are classified as andosols

Excellent physical properties

High content of OM

Problem: very high sorption capacity for P due to minerals such as allophone and imogolite –> causes P limitations in agricultural because P becomes unavailable to plants

Question 17

Why are allophanes and imogolite efficient at sorpting PO4?

Answer 17

Imogolite forms nano-tubes –> inside is very efficient in soprtion and stabilizing SOM and PO4

Allophane forms nanoballs with holes in them where PO4 can diffuse into and get occluded

Question 18

How is allophane formation and pH related?

Answer 18

Allophone formation depends on soil pH

Mostly promoted in slightly acidic onditions around pH 6

Question 19

Characteristics of andosols

Answer 19

Very fertile soils (only exception is P)

Very high porosity, good drainage, and at the same time good water holding capacity

Due to good drainage, little risk of water erostion (exception are landslides)

Question 20

What are some problems associated with andosols?

Answer 20

P-fixation

Limited recycling of OM and its nutrients

Rich in Al which can be mobilized and create Al toxicity)