Soil water balance Flashcards
Structure determines
Porosity
Bulk Density
Pore continuality
Pore size distribution
3 modes of structural decline
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
Physical degradation symptoms (4)
Crusting
Compaction
Hardsetting
Erosion
Physical degradation leads to
Retarded emergence Greater reistance to root penetration Poor heat exchange Poor water infiltration Poor gas exchange
Ramifications of physical degratation
Loss od OM
Loss nutrientsRestricted traffic
Loss production area
Desertification
Pore space affects
Infiltration Water distribution Air movement Nutrient movement erosion storage drainage = influence productivity
2 types of pores
Structural /Macro
(pore space between soil grains)
Textural/matrix
Texture vs structure:
Structure
Affected by management
Vulnerable to mechanical destruction
Unstable
Good Structure
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
Poor Soil
Crusting Erosion Compaction Root root penetration High density Poor aeration Poor water holding Poor nut retention Poor
Evaluation of Structure
Bulk density
Hydraulic Conductivity
Aggregate stability
Penetration resistance
Aggregate Stability
Ability of soil aggregates to resist disintegration when disruptive forces applied -tillage, wind, water
Why is Aggregate stability important
Water infiltration
Root Growth
Resistance to erosion
Unstable aggregates= disintegrate during rain
Dispersive soil fills surface pores, hard crist develops once it dries
Infiltration reduced =
increase run off, water erosion and decreased water available
Aggregate stability is a function of:
Clay content (kaolinite dispersicve) CEC Level of organic sunstances for bonding Ca= flocculation Na, Mg= dispersive, unstable to wetting
OM/OC
Increased OM = Inc. structure
O C is food for microorganisms = Inc. soil structure due to binding particles
Increased Clay %
= Inc. OM needed for stability
Aggregatin affects susceptibility to rain drop impact, surface sealing and erosion
3 Types of Organic Polymers
Transient - micro aggregation
Tempory - macro aggregation
Persistent - micro aggregation
Transient
Organic material rapidly decomposed by microorganisms
Additoins of plant and animal residues that are rapidly produced and rapidly decomposed
Tempory - macro aggregation
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
Persistent
Consists of extensively degraded Organic fragements
Roots, Hyphae, Bacteria
<250micron aggregates
Insentive to management
Factors affecting OC
Soil Management Plants species/crop selection Residue management Soil and nutrient loss Climate
Cultivation
Physically disturbs soil, mixing upper and lower layers
Dec. OM
Inc. BD
Changes way particles are bonded
Inc. erosion potentia;
Disk plough
Bury layer of OM built up, exposing layer of low OM at surface
Tillage Effects on Soil Properties
Aggregation Porosity % Infiltration capacity BD Soil Fauna Soil Moisture Soil Temp
Tillage effects on soil processes
Crusting Compaction Aeration Erosion Leaching OC mineralisation Evaporation
Tillage effects on crop Growth
Root development
WUE
NUE
Conventional Tillage, Stubble removal, Burning =
Dec. soil C
2 practices to decrease soil structural decline
Crop / parture rotation
NT/RT
Conservative Farming
Dec. tillage, increased platn residues = conserve soil, water and energy
Stubble buring
COntrols weeds and disease
Retention of residues is important
Protects soil surface
Decreases erosion by minimising rain drop impact
COntributes to OM
Tillage effects
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
Increased infiltration with NT due to (4)
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
Conventional Tillage
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
MT or NT Pros
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
NT cons
Increased run off due to less roughness
Higher deep drainage = nut loss to groundwater
Weeds and herbicides = her resistance
