Soil water balance

Question 1

Structure determines

Answer 1

Porosity
Bulk Density
Pore continuality
Pore size distribution

Question 2

3 modes of structural decline

Answer 2

OM linked Decline (stubble burning or cultivatio = loss of structure in surface layer

Dicline linked to a chemical problem (sodicity) = hardsettining

Decline due to cultivation of vehilce traffic

Question 3

Physical degradation symptoms (4)

Answer 3

Crusting
Compaction
Hardsetting
Erosion

Question 4

Physical degradation leads to

Answer 4

Retarded emergence
Greater reistance to root penetration
Poor heat exchange
Poor water infiltration
Poor gas exchange

Question 5

Ramifications of physical degratation

Answer 5

Loss od OM
Loss nutrientsRestricted traffic
Loss production area
Desertification

Question 6

Pore space affects

Answer 6

Infiltration
Water distribution
Air movement
Nutrient movement
erosion
storage
drainage
= influence productivity

Question 7

2 types of pores

Answer 7

Structural /Macro
(pore space between soil grains)

Textural/matrix

Question 8

Texture vs structure:

Structure

Answer 8

Affected by management

Vulnerable to mechanical destruction

Unstable

Question 9

Good Structure

Answer 9

Water stable aggregates- 1-10mm
Sufficienct pores >0.75mm for aeration
0.2-30 miromill for water holding
Little resistance to root penetration
Good infilration, water and nutrient retention
Resists erosion
Easy to work
Absence of crusting

Question 10

Poor Soil

Answer 10

Crusting
Erosion
Compaction
Root root penetration
High density
Poor aeration
Poor water holding
Poor nut retention
Poor

Question 11

Evaluation of Structure

Answer 11

Bulk density
Hydraulic Conductivity
Aggregate stability
Penetration resistance

Question 12

Aggregate Stability

Answer 12

Ability of soil aggregates to resist disintegration when disruptive forces applied -tillage, wind, water

Question 13

Why is Aggregate stability important

Answer 13

Water infiltration
Root Growth
Resistance to erosion

Unstable aggregates= disintegrate during rain
Dispersive soil fills surface pores, hard crist develops once it dries

Question 14

Infiltration reduced =

Answer 14

increase run off, water erosion and decreased water available

Question 15

Aggregate stability is a function of:

Answer 15

Clay content (kaolinite dispersicve)
CEC
Level of organic sunstances for bonding
Ca= flocculation
Na, Mg= dispersive, unstable to wetting

Question 16

OM/OC

Answer 16

Increased OM = Inc. structure

O C is food for microorganisms = Inc. soil structure due to binding particles

Question 17

Increased Clay %

Answer 17

= Inc. OM needed for stability

Aggregatin affects susceptibility to rain drop impact, surface sealing and erosion

Question 18

3 Types of Organic Polymers

Answer 18

Transient - micro aggregation
Tempory - macro aggregation
Persistent - micro aggregation

Question 19

Transient

Answer 19

Organic material rapidly decomposed by microorganisms

Additoins of plant and animal residues that are rapidly produced and rapidly decomposed

Question 20

Tempory - macro aggregation

Answer 20

Partly decomposed material of plants or microbes
1) roots - decomposable litter, food source of microbes
2) Hyphae
>250micron
Affected by management but can still last months-years

Question 21

Persistent

Answer 21

Consists of extensively degraded Organic fragements

Roots, Hyphae, Bacteria

<250micron aggregates
Insentive to management

Question 22

Factors affecting OC

Answer 22

Soil Management
Plants species/crop selection
Residue management
Soil and nutrient loss
Climate

Question 23

Cultivation

Answer 23

Physically disturbs soil, mixing upper and lower layers

Dec. OM
Inc. BD
Changes way particles are bonded
Inc. erosion potentia;

Question 24

Disk plough

Answer 24

Bury layer of OM built up, exposing layer of low OM at surface

Question 25

Tillage Effects on Soil Properties

Answer 25

``` Aggregation Porosity % Infiltration capacity BD Soil Fauna Soil Moisture Soil Temp ```

Question 26

Tillage effects on soil processes

Answer 26

``` Crusting Compaction Aeration Erosion Leaching OC mineralisation Evaporation ```

Question 27

Tillage effects on crop Growth

Answer 27

Root development WUE NUE

Question 28

Conventional Tillage, Stubble removal, Burning =

Answer 28

Dec. soil C

Question 29

2 practices to decrease soil structural decline

Answer 29

Crop / parture rotation | NT/RT

Question 30

Conservative Farming

Answer 30

Dec. tillage, increased platn residues = conserve soil, water and energy

Question 31

Stubble buring

Answer 31

COntrols weeds and disease

Question 32

Retention of residues is important

Answer 32

Protects soil surface Decreases erosion by minimising rain drop impact COntributes to OM

Question 33

Tillage effects

Answer 33

High rate of microbial breakdown due to: - Shatters macro aggregates - Mixing surface soil - Increases intensity of wet/drying cycles Movement of soil C deeper into profile = microbial breakdown

Question 34

Increased infiltration with NT due to (4)

Answer 34

Residues protecting soil against impact of rain Minimising soil dispersion and surface sealing SOil biopores open to surface - roots, worms Non disturbance = continuous soil pore system = infiltration

Question 35

Conventional Tillage

Answer 35

Inverts soil and alters nature of sturcture COntrols weeds Looses compacted soil Incorporates residues Temporarily dec. BD Inc erosion Decreased structure Dec. microbial activity = dec agg stability, inc crusting and surface sealing Large pores created by tillage collapse readily becasue of soil recompaction, consolidation and decrease in soil Organic binding agents

Question 36

MT or NT Pros

Answer 36

30% residue cover Dec BD in clong run Increase aggregate size in duplex soils Increase number and size of interconnected pores Increases earthworms Increased water retention Increased saturated hydaulic conductivity Increased yield

Question 37

NT cons

Answer 37

Increased run off due to less roughness Higher deep drainage = nut loss to groundwater Weeds and herbicides = her resistance