Compaction Flashcards
Soil subjest to 2 types of machinery traffic
Compacts - wheel
Loosens - tillage
Rresponse to traffic is described in terms of the change in
Bulk density
Porosity
Penetration resistance
What is compaction and what causes it
process by which soil grains are rearranged to decrease void space
Machinery or stock movement
Cumulative and difficault to reverse
Compacted soil properties
Increases BD
Decreases total porosity
Increases microproes
Restricts water flow
Impedes root extension
Occurs easily in wet soil
Root elongation limited by
Penetraion resistance higher than pressure exerted by root = reduced water and nutrient uptake
Preventing soil compaction
Lighter machinery
Tire widdth and pressure
Zero till
Controlled traffic
Effects of tyre width and pressure
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
Wetness of soil effect on compaction
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
Management solutions to soil compaction problems (4)
Controlled Traffic CTF
Mechanical loosening such as Deep Ripping
Primer Crops/ Bio-drilling (strong tap roots)
Addition of OM
OM addition effects
Retains soil water = rebound against compaction
Stabilises soil structure
Dec. BD and soil strength
OM addition application methods and reasoning
OM to topsoil through incorporation of plant residues is widely used
Less common to solve subsoil compaction
Technical and economical
CTF effects
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
Tramping and soil compaction
0-20cm
Fine textured soils more susceptible to trampling
Can be reduced with vegetation and prevention of grazing in wet soils
Pros of depe ripping
Subsoil/deep ripping/subsoil cultivation
Effective way to relieve subsoil compaction
Increase water conductivity
Decrease soil BD
Increase porosity
Increase water infiltration
Negatives of Deep ripping
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
Shearing stregth of soil
Depends on soil cohesion and friction
Pore water reduces soil particle contact = reduced frictional stregth
Soil can deform in 3 ways
Brittle loosening disturbance
Compressive Disturbance
Tensile Disturbance
Brittle Loosening disturbance
Soil mass fractures into smaller units
occurs due to compressive forces
Decrease in overall density but not in the clods
Compressive Disturbance
SOil is forced on itself
Density of the whole mass increases; eliminating any fissurees or macro pores initially present
Tensile disturbanve
Similar to brittle but occurs under tensile forse
Alleviating comapction
Only done by brittle and tensile disturbance
Require upward soil movement
Upward movement
If it becomes to much due to soil load, and strength of soil, soil moves laterally ratther than upwar = compressive disturbance
Confining resistance of upwards movement is dependint upon
Working depth
Soil density
moisture content
Critical Depth definition and example
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
Critical Depth depends on
Tine Geometry
Soil compressibility
Soil Density
Soil Moisture- high MC decreases critical depth
To increase critical depth:
Increase tine point width
Increase wing lift height
Relieving confining resistance
Deep tillage moisture
Too wet = smeared
Too dry = large clods/dust
idea is 50% Field capacity (late spring)
Greater water content or lower ther bulk density =
Lower critical depthand greater the susceptibility of soil to compaction
If loosening at required depth is excessive:
Reduced using narrow point
Bring working depth closer to critical depth
if desired working is greater than critcal depth, CD is increased by:
Wider tine points
Reducing confining resistance of the surface layer
Wings =
lateral extent of brittle disturbance increases
leading tines =
Greater working depth
Compaction alleviation in grassland requires
Tensile disturbance, whilst avoiding grass kill and bringing soil to the surface
Moldboard plough
Inverts soil
Turns residue under soil surface
Extreme lifting
Little residue left on surface
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
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)
Blades and Sweep ploughs
Less agressive
Reduce surface cover 10-20%
Used for stubble mulching
Grreater residue handling capacity
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
