Compaction Flashcards

1
Q

Soil subjest to 2 types of machinery traffic

A

Compacts - wheel

Loosens - tillage

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2
Q

Rresponse to traffic is described in terms of the change in

A

Bulk density
Porosity
Penetration resistance

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3
Q

What is compaction and what causes it

A

process by which soil grains are rearranged to decrease void space

Machinery or stock movement

Cumulative and difficault to reverse

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4
Q

Compacted soil properties

A

Increases BD
Decreases total porosity
Increases microproes

Restricts water flow
Impedes root extension
Occurs easily in wet soil

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5
Q

Root elongation limited by

A

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

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6
Q

Preventing soil compaction

A

Lighter machinery
Tire widdth and pressure
Zero till
Controlled traffic

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7
Q

Effects of tyre width and pressure

A

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

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8
Q

Wetness of soil effect on compaction

A

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

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9
Q

Management solutions to soil compaction problems (4)

A

Controlled Traffic CTF

Mechanical loosening such as Deep Ripping

Primer Crops/ Bio-drilling (strong tap roots)

Addition of OM

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10
Q

OM addition effects

A

Retains soil water = rebound against compaction

Stabilises soil structure

Dec. BD and soil strength

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11
Q

OM addition application methods and reasoning

A

OM to topsoil through incorporation of plant residues is widely used

Less common to solve subsoil compaction

Technical and economical

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12
Q

CTF effects

A

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

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13
Q

Tramping and soil compaction

A

0-20cm

Fine textured soils more susceptible to trampling

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

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14
Q

Pros of depe ripping

Subsoil/deep ripping/subsoil cultivation

A

Effective way to relieve subsoil compaction

Increase water conductivity

Decrease soil BD

Increase porosity

Increase water infiltration

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15
Q

Negatives of Deep ripping

A

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

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16
Q

Shearing stregth of soil

A

Depends on soil cohesion and friction

Pore water reduces soil particle contact = reduced frictional stregth

17
Q

Soil can deform in 3 ways

A

Brittle loosening disturbance

Compressive Disturbance

Tensile Disturbance

18
Q

Brittle Loosening disturbance

A

Soil mass fractures into smaller units

occurs due to compressive forces

Decrease in overall density but not in the clods

19
Q

Compressive Disturbance

A

SOil is forced on itself

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

20
Q

Tensile disturbanve

A

Similar to brittle but occurs under tensile forse

21
Q

Alleviating comapction

A

Only done by brittle and tensile disturbance

Require upward soil movement

22
Q

Upward movement

A

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

23
Q

Confining resistance of upwards movement is dependint upon

A

Working depth

Soil density

moisture content

24
Q

Critical Depth definition and example

A

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

25
Critical Depth depends on
Tine Geometry Soil compressibility Soil Density Soil Moisture- high MC decreases critical depth
26
To increase critical depth:
Increase tine point width Increase wing lift height Relieving confining resistance
27
Deep tillage moisture
Too wet = smeared Too dry = large clods/dust idea is 50% Field capacity (late spring)
28
Greater water content or lower ther bulk density =
Lower critical depthand greater the susceptibility of soil to compaction
29
If loosening at required depth is excessive:
Reduced using narrow point Bring working depth closer to critical depth
30
if desired working is greater than critcal depth, CD is increased by:
Wider tine points Reducing confining resistance of the surface layer
31
Wings =
lateral extent of brittle disturbance increases
32
leading tines =
Greater working depth
33
Compaction alleviation in grassland requires
Tensile disturbance, whilst avoiding grass kill and bringing soil to the surface
34
Moldboard plough
Inverts soil Turns residue under soil surface Extreme lifting Little residue left on surface
35
Disk plough
Large concave disks Reduces surface residue by 50-60% Better in stricky soils Good weed control Cut, invert and mix surface soil and stubble
36
Chisel plough
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)
37
Blades and Sweep ploughs
Less agressive Reduce surface cover 10-20% Used for stubble mulching Grreater residue handling capacity
38
Ripper
Break hard pan DR greater than 30cm is beneficial only in deep sandy soils Clayey soils form compacted pans at much shallower depth and