Particles, Structures and Water

Question 1

What is soil texture based on?

Answer 1

Proportion of sand, silt and clays

Question 2

Example of soil texture…

Answer 2

10% clay, 60% silt and 30% sand being sandy loam

Question 3

Example of soil porosity…

Answer 3

Clay gaps small whilst sand large

Question 4

What does porosity influecenc?

Answer 4

Drainage and water retainment

Question 5

What does texture influence?

Answer 5

Soil fertility based on storage and plant nutrient supply

Question 6

Soil Structure

Answer 6

Refers to sand/silt/clay bonded into aggreagets

Question 7

How does aggregation occur?

Answer 7

Formation then stabilisation, formation by shrinking/swelling of soil by freezing or root penetration breaking soils into discrete units

Question 8

Types of aggregate?

Answer 8

Microaggregates (<250micrometres) (Macroaggregates(>250micrometres_

Question 9

Microaggregates formation…

Answer 9

First clay flocculation where clay paritcles conglomerate

Question 10

What enhances microaggreagate microbial adegradation?

Answer 10

Organic matter association

Question 11

What does macroaggregates derive from?

Answer 11

Microaggregate coalescing

Question 12

What does stability depend on in low clay concentration?

Answer 12

OM

Question 13

What does stabilising OM consist of?

Answer 13

Plant by-products like polysaccharide glue and the other and roots and fungal hyphae

Question 14

How is pore and aggregate arrangement altered?

Answer 14

Tillage, plant roots and swelling

Question 14

How can pore space be calculated?

Answer 14

Rastio of weight to volume, as greater amount of soil particles with least amount of pore space weighs more3

Question 15

Why is pore size important?

Answer 15

Determine retention, larger pores holding water more loosley whilst smaller more tightly

Question 15

How is bulk density measured?

Answer 15

Mass of soil divided by volume of a cylinder

Question 16

Three pore classificaitons?

Answer 16

Macropores
Mesopores
Micropores

Question 17

What is soil moisture characterisitcs determined by?

Answer 17

Composition of pores

Question 18

Hyrdrualic Conducitivty

Answer 18

How easily water can move through profile, determining wetting front

Question 19

Wetting Front

Answer 19

Water infiltration moving down the profile

Question 20

What does HC depend on?

Answer 20

Water flow resistance by soil particles
Pressure generated by water in soil

Question 21

What is pressure a function of?

Answer 21

Elevation and pressure generation of overlying water columb

Question 22

What is pore resistance to water flow?

Answer 22

Determined by how well pores are connected, pore-size distribution and water ocntent of the soil

Question 23

Darcy Law

Answer 23

Refers to discharge being proportional to the loss

Question 24

Field Capacity

Answer 24

Emptying of macropores where remaining water held is within meso/micropores

Question 25

Why is aggregation important?

Answer 25

Allows withstanding slaking and compaction preventing poor water infiltration and gas exchange

Question 26

Where is aggregate instability most present?

Answer 26

Sand and silt

Question 27

Soil crusting

Answer 27

Where aggregates release into soil pores, preventing further water infilitration

Question 28

Why might water tension be bad?

Answer 28

Limit nutrient uptake due to the energy required to extract them

Question 29

What does pore size distribution determine?

Answer 29

Plant-availabe wateM

Question 30

Moisture Release Curve

Answer 30

Gives water content against water tension

Question 31

Why shouuld large and small pores be balanced?

Answer 31

Gas exchange and water storage

Question 32

What are the best agriculture soils?

Answer 32

Loamy textures with equal silt, clay and sand for enough water for plant growht and pores for gas exchange