Compaction

Question 1

Soil subjest to 2 types of machinery traffic

Answer 1

Compacts - wheel

Loosens - tillage

Question 2

Rresponse to traffic is described in terms of the change in

Answer 2

Bulk density
Porosity
Penetration resistance

Question 3

What is compaction and what causes it

Answer 3

process by which soil grains are rearranged to decrease void space

Machinery or stock movement

Cumulative and difficault to reverse

Question 4

Compacted soil properties

Answer 4

Increases BD
Decreases total porosity
Increases microproes

Restricts water flow
Impedes root extension
Occurs easily in wet soil

Question 5

Root elongation limited by

Answer 5

Penetraion resistance higher than pressure exerted by root = reduced water and nutrient uptake

Question 6

Preventing soil compaction

Answer 6

Lighter machinery
Tire widdth and pressure
Zero till
Controlled traffic

Question 7

Effects of tyre width and pressure

Answer 7

Increasing tyre width or decreasing pressure= spreads compaction pressure over a wider area

Low pressure reduces rut depth and soil damage but increases total area wheeled

Question 8

Wetness of soil effect on compaction

Answer 8

Dry soil not easily compacted

Saturated soil is also not easily compacted because water is not compressible which fills big pores

Moist soil is more compactable

Question 9

Management solutions to soil compaction problems (4)

Answer 9

Controlled Traffic CTF

Mechanical loosening such as Deep Ripping

Primer Crops/ Bio-drilling (strong tap roots)

Addition of OM

Question 10

OM addition effects

Answer 10

Retains soil water = rebound against compaction

Stabilises soil structure

Dec. BD and soil strength

Question 11

OM addition application methods and reasoning

Answer 11

OM to topsoil through incorporation of plant residues is widely used

Less common to solve subsoil compaction

Technical and economical

Question 12

CTF effects

Answer 12

ZT decreases operations but still 50% field area affected by heavy vehicle traffic

CT = permanent, compacted lanes leaving loose rooting zone

Recompaction of a deep tilled soil can be prevented using CT system

Question 13

Tramping and soil compaction

Answer 13

0-20cm

Fine textured soils more susceptible to trampling

Can be reduced with vegetation and prevention of grazing in wet soils

Question 14

Pros of depe ripping

Subsoil/deep ripping/subsoil cultivation

Answer 14

Effective way to relieve subsoil compaction

Increase water conductivity

Decrease soil BD

Increase porosity

Increase water infiltration

Question 15

Negatives of Deep ripping

Answer 15

Recompaction - subsequent machinery and animals

COst - fuel, reduced if using machinery with shallow leading tines and winged shanks

Soil mixing - deep cultivation that inverts soil may also bring dispersive subsoil to the soil surface

Question 16

Shearing stregth of soil

Answer 16

Depends on soil cohesion and friction

Pore water reduces soil particle contact = reduced frictional stregth

Question 17

Soil can deform in 3 ways

Answer 17

Brittle loosening disturbance

Compressive Disturbance

Tensile Disturbance

Question 18

Brittle Loosening disturbance

Answer 18

Soil mass fractures into smaller units

occurs due to compressive forces

Decrease in overall density but not in the clods

Question 19

Compressive Disturbance

Answer 19

SOil is forced on itself

Density of the whole mass increases; eliminating any fissurees or macro pores initially present

Question 20

Tensile disturbanve

Answer 20

Similar to brittle but occurs under tensile forse

Question 21

Alleviating comapction

Answer 21

Only done by brittle and tensile disturbance

Require upward soil movement

Question 22

Upward movement

Answer 22

If it becomes to much due to soil load, and strength of soil, soil moves laterally ratther than upwar = compressive disturbance

Question 23

Confining resistance of upwards movement is dependint upon

Answer 23

Working depth

Soil density

moisture content

Question 24

Critical Depth definition and example

Answer 24

Transition working depth above which the desired brittle type of disturbance occurs and below which a compressive disturbance occurs

Compaction at plough depth (plough an) is due to compressive disturbance below critical depth

Question 25

Critical Depth depends on

Answer 25

Tine Geometry

Soil compressibility

Soil Density

Soil Moisture- high MC decreases critical depth

Question 26

To increase critical depth:

Answer 26

Increase tine point width

Increase wing lift height

Relieving confining resistance

Question 27

Deep tillage moisture

Answer 27

Too wet = smeared

Too dry = large clods/dust

idea is 50% Field capacity (late spring)

Question 28

Greater water content or lower ther bulk density =

Answer 28

Lower critical depthand greater the susceptibility of soil to compaction

Question 29

If loosening at required depth is excessive:

Answer 29

Reduced using narrow point

Bring working depth closer to critical depth

Question 30

if desired working is greater than critcal depth, CD is increased by:

Answer 30

Wider tine points

Reducing confining resistance of the surface layer

Question 31

Wings =

Answer 31

lateral extent of brittle disturbance increases

Question 32

leading tines =

Answer 32

Greater working depth

Question 33

Compaction alleviation in grassland requires

Answer 33

Tensile disturbance, whilst avoiding grass kill and bringing soil to the surface

Question 34

Moldboard plough

Answer 34

Inverts soil
Turns residue under soil surface
Extreme lifting
Little residue left on surface

Question 35

Disk plough

Answer 35

Large concave disks
Reduces surface residue by 50-60%

Better in stricky soils

Good weed control

Cut, invert and mix surface soil and stubble

Question 36

Chisel plough

Answer 36

Heavy duty tines

Less inversion of soil and crop residue incorportaiton

Uses chisels or sweeps that shatter the soil and good for weed control

Reduce residue 12-50%

Higher risk of disease for tillage with blade/chisel than disk plough (stubble incorporated)

Question 37

Blades and Sweep ploughs

Answer 37

Less agressive
Reduce surface cover 10-20%

Used for stubble mulching

Grreater residue handling capacity

Question 38

Ripper

Answer 38

Break hard pan

DR greater than 30cm is beneficial only in deep sandy soils

Clayey soils form compacted pans at much shallower depth and