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Quality Of Soils Flashcards

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1
Q

What is a soil function?

A

A service that the soil gives to the environment

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2
Q

Examples of soil functions

A

Food, fibre, fuel
Carbon store
Water purification
Climate regulation
Nutrient cycling
Habitat
Flood regulation
Pharmaceutical
Infrastructure
Construction material
Cultural heritage

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3
Q

Soil health

Soil quality

A

Self regulation, stability, resilience, lack of stress

Properties of soil that are fit to perform particular functions

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4
Q

Soil formation factors

A

Parent material
Topography
Biology
Climate
Time

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5
Q

Soil Horizons

A

O Horizon = organic top layer
A Horizon = topsoil
B Horizon = subsoil
C Horizon = substratum
R Horizon = bedrock

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6
Q

What does surface area influence?

A

Increased water retention - more pores
Increased nutrient retention
Nutrient release
Soil particle flocculation
Microorganism activity

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7
Q

When are soils no longer mineral?

A

10% organic mineral soil
50% pure peat

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8
Q

Primary particle

A

Sand
Silt
Clay

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9
Q

What is an aggregate?

A

Soil unit made of primary particles with binding agents

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10
Q

What is a Ped?

A

Structural unit formed of aggregates

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11
Q

What is a Clod?

A

Structural unit formed by artificial process eg traffic, cultivations

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12
Q

Friability

A

Ability of soil to break apart

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13
Q

What is Plastic limit?

A

Moisture content at which soil starts to behave plastic (smear)

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14
Q

What is Liquid limit?

A

Moisture content to cause a plastic soil to behave as a liquid

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15
Q

What is Soil aggregation?

A

Macro aggregates compromised of micro aggregates formed by aggregation

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16
Q

Factors influencing aggregation

A

Physical-chemical: clay flocculation and cation exchange, volume changes in clays (wet-dry), oxides acting like cement (tropics)

Biological: soil organisms (burrowing, hyphae, glues), organic matter, tillage

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17
Q

Aggregates can be destabilised by:

A

Forces of impact - rain
Slaking - dry to wet
Micro cracking by swelling - gradual wetting
Dispersion - sodium

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18
Q

Consequence of poor soil aggregation?

A

Breakdown of structure
Pore clogging
Erosion
Reduced infiltration
No protection of organic matter
Reduced habitat
Less aeration

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19
Q

Bulk Density

A

Mass of a unit volume of dry soil
- includes solids and pore space
- need known volume of soil (core)

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20
Q

Size and function of pores?

A

Macropores - transport of water and air, drain under gravity, found in sand, larger aggregates and peds

Mesopores - air/water store

Micropores - filled with water, clay, inaccessible to roots

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21
Q

Effects on bulk density of:
- traffic
- soil texture = more sand
- organic matter
- tillage

A
  • increase = compactability
  • increase = less pore space
  • decrease = more pore space, OM lighter then minerals
  • increase long term = loss of OM, weakened soil structure
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22
Q

Impact of compaction on bulk density

A

Increased bulk density
Root growth inhibited by soil resistance to penetration, poor aeration, reduced movement of water and nutrients, potential anaerobism

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23
Q

What is Tilth?

A

Relies on friability - good cohesion of individual aggregates
Depends on texture, aggregate stability, moisture, density, organic matter

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24
Q

Soil capillarity

A

Water can move up through adhesion and cohesion
More capillary flow in fine structures = smaller pore space

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25
Soil water potential
Gravitational Matric (pressure) = capillary - unsaturated zone Osmotic - low to high potential
26
Field saturation to wilting point
When field at saturation water lost through gravitational Field capacity = water held by matric Wilting point = no more water available to plants
27
Plant available water
Water retained in soil between field capacity and wilting point Silt has the most
28
What factors influence soil water for plant uptake?
Texture - finer particles more available, some clays lock up water in micropores Organic matter - improved structure + high water holding capacity Structure - reduced porosity and infiltration Osmotic potential - more soluble salts in solution Soil depth and horizons
29
Benefits of drainage
Soil workability Enhanced root growth Reduced disease Rapid soil warming Reduced gas Removal of salts
30
Gases in soil
Oxygen - aerobic respiration CO2 - toxic above 10% Water vapour, methane, N2O
31
Aeration and influenced
To supply oxygen and remove harmful gasses Drainage, soil respiration, depth, pore size
32
Effects of Soil temperature
Effects germination, root functions, microbial processes, freeze-thaw Influenced by pore space, water, slope/aspect, colour, rainfall, soil cover
33
What is Cation exchange
Positively charged cations are attracted to negative charges on clay and OM Cations replace one another charge for charge
34
what is Cation exchange capacity
Sum of total exchangeable cations that a soil can hold Organic being highest then clay and sand lowest
35
Why would we use Gypsum
Sodium causes deflocculation Gypsum works by calcium displacing the sodium and allowing better flocculation Same with magnesium (causes swelling and shrinking)
36
Sources of H+
Oxidation of N Root respiration OM Acid rain Plant uptake of cations
37
Effects of soil pH
Al and Fe toxicity at low ph Nutrient availability - lack of Mn at high and Ca at low Bacteria less active at low Disease - club root at low common scab at high
38
Liming
Must displace H+ from exchange sites Neutralise them in solution Liming materials with lower neutralising value must be applied in higher cuantities depending on pH and texture
39
Macronutrients
N P K Mg Ca S
40
Micronutrients
Mn Cu B Mo Zn Fe Co Se Ni
41
Nutrient Interactions
Antagonism - high N = low B Stimulation - high N = high Mg
42
N deficiency
Makes up plant proteins Yellowing of older leaves Sands, low OM, leaching, anaerobic
43
P deficiency
Needed for ATP Stunting High/low pH, high erosion
44
How to increase nutrient efficiency?
Nutrient management plan Ph Structure for roots
45
How much carbon in organic matter?
0.58kg C in 1kg OM
46
What is detritus?
Remains of dead plant and animal material Undergoes decomposition into humus
47
What is plant residue?
Sugars, starches, simple proteins Crude proteins Hemicellulose Cellulose Fats and waxes Lignin
48
What is Decomposition?
Microorganisms break down organic compounds in presence of oxygen Essential nutrients released and/or immobilised New compounds are synthesised by microbes Some compounds locked up in soil
49
What is humus made up of?
Fulvic acids Humic acids Humins - water holding, soil structure, stability, CEC
50
Influence of OM on soil
Soil colour Soil aggregation and stability - reduces erosion increases aeration and C store Soil workability - reduces plasticity Infiltration and water holding capacity - more pore space Cation exchange capacity Nutrient slow release Soil biology
51
How is OM built up or lost
Plant residues, animal inputs, biomaterial, root residues, rhizodposition Oxidation, erosion, leaching, removal off-site
52
Environmental factors influencing OM
Temperature - low = faster accumulation, high = slower accumulation Moisture pH Residue location
53
CN ratio
CN ratio of residues determine rate of decay and rate of available N Microorganisms need 8:1 but due to respiration loss need 24:1 High CN ratio causes depletion in N (immobilisation) Low CN release more soluble N but too much can result in anaerobic
54
Management influences on OM
Organic amendments - compost best then FYM Cover crops Reduced tillage Grass leys
55
Microbiota
Viruses Bacteria Archaea
56
Important soil bacteria
N fixing = Azotobacter, rhizobacteria Nitifrifcation = Proteobacteria Mineralisation = Actinobacteria Denitrification = Pseudomonas Disease = pectobacteria (blackleg)
57
Important soil Archaea
Extreme halophiles - salt Methanogens - methane
58
Importance of soil bacteria and archaea
Release and recycle nutrients Mutualistic symbionts - biofertilisers Plant pathogens - biopesticides
59
Types of fungi
Saprotrophs - feed on dead tissue Mutualists - mycorrhizal fungi Parasites or pathogens
60
Importance of fungi
Release and recycle nutrients Decomposers Mutualistic symbionts Soil structure - glomalin
61
Microfauna
Protozoa - feed on bacteria, mineralise nutrients and release N Nematodes - mineralise and release nutrients, plant pathogen Rotifers - feed on detritus, dead bacteria and Protozoa
62
Nitrogen cycle processes
N fixation: N2 - ammonium Nitrification: ammonia - nitrite - nitrate Denitrification: nitrates into N gas Mineralisation: organic N into available N Immobilisation: uptake of N by plants o organisms
63
Microorganisms with N fixing
Free living e.g. Azotobacter Bacteria associated within rhizosphere Phototrophic N fixing bacteria Symbiotic N fixing e.g. Rhizobium in legumes
64
Microorganism for nitrification
Proteobacteria for ammonia and nitrate oxidisers e.g. Nitrobacter for nitrate Causes acidification
65
Microorganism for Denitrification
Pseudomonas bacteria
66
P forms in the soil
Soluble P - plant available Organic P - within microbes and plants Inorganic P - locked up
67
What is P mineralisation and immobilisation?
Organic P into P P into organic P Influenced by soil moisture, temperature, pH and microbial population
68
P adsorption
P attached to soil particles by clay, Al, Fe oxides pH dependent, highest available at 6.5
69
Factors influencing P availability
OM - mineralisation + release P from soil Clay - locks up P Soil mineralogy - Fe and Al locks up P Soil pH - 6.5 Abiotic factors
70
P microorganisms
Bacteria, fungi Mycorrhizal fungi form Mutualistic symbiosis - P in exchange for carbohydrates Can be outside (ectomycorrhizas) and inside (arbuscular mycorrhizas) the root
71
Benefits of mycorrhizal fungi
Improved nutrient uptake Increased soil stability Resistance against pathogens and herbivores Improve water balance Alleviate abiotic stress
72
What is the rhizosphere?
The soil volume around roots that is strongly affected by root functioning Roots release enzymes, H+, CO2, exudates Roots uptake nutrients, O2 and water
73
Rhizosphere interactions
Positive: Mutualistic symbiosis, growth facilitators, biocontrol Negative: Phytotoxins, pathogens, root herbivores
74
Allelopathy and Autotoxicity
Chemical mediated plant-plant interference where phytotoxins released to reduce survival of neighbours Plant or decomposing residues release toxins to prevent germination of same species
75
Farm practices and the rhizosphere
Crop rotation - reduce allelopathy, crop cover maintains temperature and moisture Tillage - less tillage increased biodiversity Nutrients Mulching
76
Mesofauna size and examples
0.2 micromilimeters - 2mm Tardigrades - feed on bacteria, plant cells, Protozoa, Rotifera and nematodes. Survive extreme conditions Springtails - decomposers, feed on bacteria, fungi, nematodes. Different ecotypes. Mites - break down OM and feed on fungi and bacteria Important for nutrient cycling by feeding and being prey
77
Macro fauna size and examples
Over 2mm Pot worms - feed on bacteria, fungi, OM decomp Thrips Centipedes - predators, venomous Millipedes - detritivores Pseudocentipedes - decaying vegetation, seeds, roots Earthworms Wireworms Ground beetles
78
Types of Earthworms
Epigeic - small, litter dwelling Endogeic - small to medium, horizontal burrows Anecic - large, deep vertical burrows Good indicators of soil health - improve structure and decomposers Earthworm counts - AHDB
79
Assessing soil quality
Physical: Texture - hand, laser diffraction, VESS - 1-5, infiltration rates, penetrometer, bulk density Chemical: pH, PK, Mg - lab, W pattern 15cm, N - blocks of 30cm, C Biological: earthworm count, SOM - loss of ignition (LOI), microbial activity - respiration rates underpant test, taxonomy ID, DNA
80
Gas analysis
Flux tower Dynamic chambers Static chambers
81
What is conservation ag and regen ag
Minimum soil disturbance, permanent soil cover, diverse crop rotation Plus: living roots, livestock
82
Management options for improving soil quality
Tillage - mintill, no till, strip till Rotation - early winter cereals, grasses, spring cereals after cover crop Cover crops Leys and grazing Mulching Organic manures Drainage Nutrient management plan Pesticide use Biostimulants Windbreaks/shelterbelts Agroforestry Buffer strips
83
Soil policy
Sustainable development goals 4 per mile - increase SOM by 0.4% a year 25 year environmental plan - soils must be managed sustainably ELMS - SFIs - soil management plan, cover crops, herbal leys, no till farming, NVZ Farming rules for water Catchment sensitive farming

Advanced Soils (2 decks)

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