Soil

Question 1

What are the five factors of soil formation?

Answer 1

*Climate
*Organisms
*Relief
*Parent material
*Time

Question 2

How can climate impact soil formation?

Answer 2

Temperature and moisture (rainfall), freeze-thaw effects, Influences speed of chemical & physical weathering of parent material, Influences activity of soil organisms, Influences speed of decomposition of dead organisms, Soils develop faster in warm/moist climates and slower in cold/arid climates, High amounts of precipitation results in leaching of minerals and nutrients

Question 3

How can organisms impact soil formation?

Answer 3

Input of organic matter, e.g,. decaying plants, necromass, nutrient cycling, bioturbation (soil mixing), higher activity speeds up soil formation

Question 4

How can relief impact soil formation?

Answer 4

Slope and aspect, sunlight hours, temperature, water runoff, erosion, organic matter buildup, and position in the landscape determine if the soil receives or leaches nutrients

Question 5

How can parent material impact soil formation?

Answer 5

The physical, chemical, and mineralogical composition of unconsolidated material influences texture, structure, drainage, and chemistry. Mode of transportation is important e.g. ice-glacial till-, flowing water-alluvium-, gravity-colluvium-, wind-tephra, loess, Aeolian-, Lake-Lacustrine-, Ocean-marine-, in place-residual

Question 6

How can time impact soil formation?

Answer 6

Soils are not static; soils develop and change over time. Older soils are more weathered than younger soils, and soils in the tropics tend to be old, not affected by remixing due to glaciation

Question 7

What are the anthropogenic factors that impact soil?

Answer 7

*Building materials e.g., concrete, aggregates, bricks
*Machinery and movement of soils
*Soil amendments e.g., compost, fertilizer, pesticides, lime, sewage sludge
*Removal of biomass (organic matter not returned to the soil)
*Land-use and erosion
*Climate change, an increase in extreme weather events
*Increased CO2 speeds up the dissolution of rocks (more carbonic acid in the rain)
*Construction and urbanization are altering the topography
*Terracing

Question 8

Who developed the UK’s soil classification system?

Answer 8

Soil Survey of England and Wales

Question 9

What is a soil profile?

Answer 9

A series of soil layers or horizons that can be seen when you dig a hole

Question 10

What is a soil catena?

Answer 10

A group of soils in a landscape

Question 11

What is a soil series?

Answer 11

Similar profiles, under similar conditions on one parent material, usually have a geographical name suggesting where they were first mapped

Question 12

How many soil series are currently recognised?

Answer 12

753 soil series are currently recognized, and the most detailed level of soil classification

Question 13

What are soil horizons?

Answer 13

Distinct layers within a soil profile, each with unique characteristics resulting from soil-forming processes.

Question 14

What are the 10 types of UK soils?

Answer 14

*Terrestrial raw soils
*Lithomorphic soils
*Brown soils
*Grown-water gley soils
*Raw gleys soils
*Pelosols
*Podzolic soils
*Surface-water gley soils
*Man-made soils
*Peat soils

Question 15

Characteristics of Terrestrial Raw Soils

Answer 15

Formed in very recent parent material, not significantly altered by soil-forming processes, with no pedogenic horizons, mainly on coastal sand dunes. They are nutrient-poor, moisture-deficient, high salinity, poor structure, sand texture, and wind erosion-prone.

Question 16

Characteristics of Lithomorphic Soils

Answer 16

Mainly rock and soil, shallow soils in which the only significant pedogenic process has been the formation of an organically enriched surface horizon, two types: **

Question 17

What are the two types of Lithomorphic soils?

Answer 17

*rankers (non-calcareous): Nutrient poor, freely draining, low salinity, highly organic, not erosion-prone, oxic, no CaCO3, low pH (<pH 5), acid parent material

*rendzinas (calcareous): nutrient-rich, freely draining, low salinity, highly organic, not erosion-prone, oxic, abundant CaCO3, high pH (>pH 7.5)

Question 18

Characteristics of Brown Soils

Answer 18

One of the most common types (45%), pedogenic processes have produced predominantly brownish or reddish subsurface horizons, freely draining, mostly in agricultural use, high biological activity, earthworm mixing, and channels (Broad transition zones rather than clear horizon boundaries), nutrient-rich, low salinity, mod-high organic matter mixed through the profile, not erosion-prone, loam texture, oxic, not much CaC03, medium pH, highly crumb structure.

Question 19

Characteristics of Groundwater Gley Soils

Answer 19

Soils that have prominently mottle or grey subsoils resulting from periodic waterlogging by a fluctuating groundwater table (stems from the topographic position rather than draining soil), moderate nutrients, poorly draining, low salinity, high organic matter at the surface, not erosion-prone, mottles, silty-clay texture, earthworms only at surface, anoxic, can be CaCO3, medium pH (pH 5-7), poor structure

Question 20

Characteristics of Raw Gley Soils

Answer 20

High salinity, salt marshes, and intertidal mud flats occur in mineral material that has remained waterlogged since deposition, nutrient-rich, poor structure, water erosion-prone, anoxic, silt texture, high CaCO3, and high pH

Question 21

Characteristics of Pelosols

Answer 21

Slowly permeable soils, very rich in clay with no waterlogging, crack deeply in dry seasons and have a coarse blocky or prismatic structure, nutrient-rich, not well draining, low salinity, moderate organic matter, not erosion prone clay texture, deep cracking, oxic, not much CaCo3, medium pH, high structure.

Question 22

Characteristics of Podzolic Soils

Answer 22

Horizon structure, soils with a subsurface accumulation of Fe or Al, normally formed from acid weathering conditions and under natural or semi-natural vegetation (e.g., conifer or heath), have an unincorporated acid organic layer at the surface,a characteristic bleached horizon, and often have an iron pan at depth

Question 23

Characteristics of Surface-water Gley Soils

Answer 23

Named after the gleying process, seasonally waterlogged, slowly permeable, series of chemical reactions when O2 is in short supply, chemical reduction of Fe3+ → Fe2+, causes mottling in the surface horizon, Fe2+ bluish/greyish/green, Fe3+ yellow/brown/red, moderate nutrients, poorly draining, compaction layer at depth, low salinity, can be high organic matter at the surface, not erosion-prone, mottles, silty-clay texture, no earthworms, anoxic, can be CaCO3, medium pH, poor structure.

Question 24

Characteristics of Man-made Soils

Answer 24

Soils formed in material modified or created by human activity, created from abnormal management, moderate nutrients, poorly draining, compacted, can be contaminated, often anoxic, with poor structure

Question 25

Characteristics of Peat Soils

Answer 25

Organic soils derived from partially decomposed plant remains that accumulate under waterlogged conditions, e.g., Oligotrophic peat and Eutrophic peats, decomposition is prevented as conditions are either too wet or too acidic, has to be more than 40cm and 50% organic matter

Question 26

What are the 15 global soil regions?

Answer 26

Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, Vertisols, Rocky land, Shifting sand, Ice/Glacier

Question 27

What are Gelisols?

Answer 27

Soils that are permeated frozen, contain permafrost within 100cm of the soil surface, contain ‘gelic material’ (material affected by cryoturbation- frost churning), found in tundra and cold-weather environments, carbon reservoir, climate change has potential to thaw and release trapped carbon

Question 28

What are Andisols?

Answer 28

Volcanic-ash and pumice parent material, relatively light and porous, high cation exchange capacity, high water holding capacity, rich in allophane and imogolite (weathering products of volcanic ash)

Question 29

What are Oxisols?

Answer 29

Formed in the tropics, highly weathered, dominated by oxides of Fe and Al, distinctive red color, very deep, low in natural fertility (leaching of base cations), high acidity, require extensive inputs to be productive (lime and fertilizers)

Question 30

What are the two types of Peat Soils?

Answer 30

-*Eutrophic peat: formed in lowlands, water drains in from surrounding areas to basin, high nutrients, poorly draining, shallow water tables, low salinity, high organic matter, not erosion-prone, no earthworms, anoxic, can be CaCo3 underlying, moderate pH, undecomposed organic (spongy) structure, e.g., Cors Eddreiniog, originate as open water, gradually filled in by reedbeds, sedges followed by woodland *Oligotrophic peats: formed in uplands, water from high rainfall in uplands, low nutrients, poorly draining, shallow water table, low salinity, high organic matter, erosion-prone, no earthworms (Too acidic), anoxic, no CaCO3, low pH, undecomposed organic (spongy) structure, E.g., raised bog and blanket bog

Question 31

What are Vertisols?

Answer 31

Clay-rich, shrink and swell characteristics, dark colored, most common in warm sub-humid or semi-arid climates

Question 32

What are Utisols?

Answer 32

Tropical weathered soils, geologically old landscape settings, subsurface clay accumulations, low fertility, high acidity

Question 33

What are Aridisols?

Answer 33

Formed in arid, desert climates, dry soils, often have accumulations of CaCo3 (Lime), Na or salts, light in color, low organic matter, irrigation necessary for production

Question 34

What is weathering?

Answer 34

Breakdown of rocks at the earth’s surface

Question 35

What are the three types of weathering?

Answer 35

*Physical: weakening and disintegration of rocks by physical force *Chemical: weakening and disintegration of rocks by chemical reactions *Biological: weakening and disintegration of rocks by plants, animals, and microbes

Question 36

What are the five types of physical weathering?

Answer 36

*Thermal expansion: extreme temperatures cause rocks to expand and retract *Abrasion *Salt Crystal growth: salt dissolves in water and runs down into cracks in rocks, expansion forces cracks *Sheeting/exfoliation: as the rock is buried underground, pressure is applied, and when pressure is released, the rock cracks. *Frost wedging: expands when frozen water creates pressure and then breaks rock apart

Question 37

What are the four types of chemical weathering?

Answer 37

*Carbonation: acid causes the rock to dissolve e.g. carbonic acid *Oxidation: iron-rich rocks getting ‘rusty’ color *Hydrolysis: new solution when minerals are mixed with water e.g. Na-minerals forming saltwater solution *Hydration: chemical bonds change on interaction with water e.g. Anhydrite reacts with groundwater to form gypsum

Question 38

What are the five types of biological weathering?

Answer 38

*Root wedging: grow through the gaps in the rocks breaking it apart *Rock-boring bivalves: eat away at the rock to create holes e.g. piddock *Root and fungal exudates: tree roots grow through bedrock, weakening rock as well as releasing chemicals, rocks break apart *Microbial weathering of rocks and minerals: nutrient depletion and minerals causing weathering, metabolic activity, and use up carbon* *Lichen and moss: primary colonizers of bare rock and recent lava flows, excretion of organic acids e.g. oxalic acid (dissolve minerals and chelate metallic cations)

Question 39

What are the two types of minerals?

Answer 39

*Primary minerals: little change in composition since extruded in molten lava, most prominent in sand and silt fractions e.g. quartz, mica, feldspars *Secondary minerals: formed by the breakdown and weathering of minerals as soil formation progressed, clay friction, e.g. silicate clays, iron oxides, aluminum oxides

Question 40

What do chemical reactions in soils do?

Answer 40

*Controls pollutant movement: heavy metals, acid rain, eutrophication, drinking water *Controls productivity: agricultural productivity, forest productivity, environmental remediation

Question 41

What are cations?

Answer 41

Positively charged ions in the soil. They are mobile with soil water, attracted to some soil particles (generally have a negative surface charge), other cations in solution can displace absorbed cations. Displacement of cations depends on relative concentration and number of charges on cation.

Question 42

What are anions?

Answer 42

Negatively charged ions in the soil

Question 43

What is CEC?

Answer 43

Cation exchange capacity, which is the total amount of cations a soil can hold

Question 44

What are the sources of cations in soils?

Answer 44

Decomposition of organic matter, weathering (breakdown) of minerals, addition in fertilizers, addition in dry and wet deposition (rainfall)

Question 45

What are the key properties of clay?

Answer 45

Clay particles are <2 μm, the smallest soil minerals. There are many types of clay: Kaolinite, Vermiculite, Smectite, and Illite. Each type of clay has a different chemistry and all clays are negatively charged, and all clays bind positively charged cations e.g. Kaolinite, formed from weathered feldspar, 1:1 mineral, Simplest clay mineral (Aluminium silicate mineral), Common in tropical soils

Question 46

What is Isomorphous substitution?

Answer 46

This type of charge is permanent and is the replacement of one atom by another of similar size in a crystal lattice without changing the crystal structure of the mineral.

Question 47

What are broken edges?

Answer 47

This type of charge is variable, hydroxides create negative charges at edges of clay, all types of clay have this type of charge

Question 48

What is chemotaxis?

Answer 48

The movement of microbes towards a specific stimulus

Question 49

What are the key properties of Soil Organic Matter?

Answer 49

*Increases soil surface area *Increases water holding capacity *Improves buffering capacity: able to retain irons in the soil for microorganisms to break it down *Increases soil biotic activity *CHO (Carbon, Hydrogen, Oxygen), NPS (Nitrogen, Phosphorous, Sulphur), and Carbon storage

Question 50

What is the difference between Soil Organic Matter (SOM) and Soil Organic Carbon (SOC)?

Answer 50

SOM is the mass of biotic-derived material in soil, reduced Carbon, and HON (Hydrogen, Oxygen, Nitrogen) whereas SOC is only the carbon in soil organic matter

Question 51

What are the two types of inorganic carbon in soil?

Answer 51

*Geogenic: parent material, limestone, or calcareous sediments *Pedogenic or biogenic: microbial and root respiration, accumulates at a depth of normal transport

Question 52

What are the four classes of organic materials?

Answer 52

*Living (biota) *Really dead (partially decomposed) *Dead (Fresh litter) *Really-really- dead (humus)

Question 53

What do macrofauna do for SOM?

Answer 53

Ingest OM (Organic matter) and excrete decomposed OM, worm casts have enriched nutrient content, available forms for plant uptake (can be hotspots of N20 production), burrowing activity increases aeration of the soil and improves drainage

Question 54

What is organic matter?

Answer 54

Living (microbial community), metabolic (amino acids, carbohydrates), slow (fats, waxes, lignin), passive (humus)

Question 55

What is humus?

Answer 55

The dark, stable, nutrient-rich organic matter in soil that improves its structure, water retention, and fertility.

Question 56

How are humic materials formed?

Answer 56

Formed from a combination of biotic and abiotic reactions, high charge density, high water holding capacity, pH-dependent charge

Question 57

What is the key driver of soil carbon efflux?

Answer 57

Soil respiration

Question 58

Why is dissolved organic matter significant?

Answer 58

It provides the main source of carbon needed for many biogeochemical processes within the soil.

Question 59

What is Dissolved organic matter split into?

Answer 59

*High molecular weight compounds: makes up the majority, mainly humic substances, slow turnover *Low molecular weight compounds: less than 10%, exuded into rhizosphere, fast turnover

Question 60

Why does SOM persist?

Answer 60

*Resupply of organic matter *Recalcitrance of organic molecules *Protection: chemical and physical

Question 61

What are soil aggregates?

Answer 61

Stable clumps of soil particles bound together by organic matter, clay, and biological activity, creating essential pore spaces for water, air, and root movement.

Question 62

What do soils help?

Answer 62

*Offset greenhouse gas emissions *Enhance soil structure *Improve water holding capacity *Soil aggregate stability = better infiltration

Question 63

How are soils resilient?

Answer 63

*They are not killed by fire *Survive invasions *Endure human disturbance

Question 64

How much of the UK's terrestrial carbon do soils hold?

Answer 64

10 Billion tonnes

Question 65

What are the main drivers impacting soil organic matter

Answer 65

*Changes in land use *Land management *Climate change

Question 66

What are the effects of land management on soil carbon?

Answer 66

*Drainage *Tillage operations *Management that increases risk of erosion *Reliance on inorganic fertilisers only *Removal of crop residues *Application of organic manures

Question 67

How to combat SOM loss?

Answer 67

*Block ditches in vulnerable peatlands *Stop using peat soils for agricultural/horticultural purposes *Convert land uses, e.g. arable to grass or woodland, grass to woodland *Adopt measures to reduce soil erosion losses *Reduce cultivation (surface operations vs plough)? *Apply livestock manures and other organic resources *Intercropping and cover crops *Breed crops with larger/deeper root systems? *Biochar: preta-soils

Question 68

What is the Global: 4 per 1000 initiative?

Answer 68

If we could increase the top soil carbon content to 0.4% per year, we could offset all carbon dioxide emissions

Question 69

What are the five types of subsoil carbon sequestration measures?

Answer 69

*Deep rooting plants *Deep burial of organic matter *Clay burial *Deep ploughing *Iron addition

Question 70

Why are roots important?

Answer 70

They anchor the plant, absorb water and nutrients, store nutrients and they can sense the environment.

Question 71

What is the roots anatomy?

Answer 71

*Epidermis: the outer layer of skin *Ground/cortex: tissue in between epidermis and vascular tissue (mainly parenchyma cells) *Stele: the ore of vascular tissue: *Xylem: water transport *Phloem: food transport *Pericycle: the layer of cells that can produce lateral roots *Apical meristem: zone of cell division i.e. stem cells, can become any type of tissue, starting point for primary growth, three primary meristems for development of the three types of tissue *Quiescent center: store of stem cells

Question 72

What are the three types of ground tissue?

Answer 72

*Parenchyma cells: forms cortex of roots, living thin-walled cells, large central vacuoles, storage of food and water, chlorenchyma (parenchyma containing chloroplasts) *Collenchyma cells: living thin-walled cells, areas of secondary thickening *(with cellulose)*, some structural support, provide tensile strength, generally elongated *Sclerenchyma cells: two types (fibers and sclereids), dead thick-walled cells, strengthened by cellulose, hemicellulose, and lignin, no intercellular air spaces, mechanical support and protection

Question 73

What are lateral roots?

Answer 73

Each lateral root has its own root cap and meristem (zone of cell division) that grows through the cortex. In fibrous root systems, there is much lateral root formation.

Question 74

What are the functions of root caps?

Answer 74

*Protects the growing tip *Secretes mucilage, facilitating movement through the soil *Statcyctes allow for gravity perception *(gravitropism):* - contain statoliths = starch-filled amyloplastic organelles - sediment at the lowest point in the cell triggering auxin production and redistribution *Slough cells/border cells *Communication with soil microbiota

Question 75

What are the functions of border cells?

Answer 75

*Sloughed cells remain metabolically active *biological ‘goalies’ = neutralize dangers to newly generated root tissue *Attract and immobilize root-feeding nematodes *defensive structures against fungal attack *control growth/gene expression in symbiotic bacteria *Repel/bind pathogenic bacteria *Protecting against toxic Al3+

Question 76

What are the functions of root hairs?

Answer 76

*Root hairs increase surface area *Root hairs secrete acid (H+) *H+ cation exchange with minerals *Mineral uptake into roots *Apoplast route: inter-cellular spaces within the root cortex along which water and solutes can diffuse *Symplast route: channels through cells along which water and solutes are actively transported.

Question 77

What is involved in nutrient movement?

Answer 77

Roots intercept some nutrients as they grow, and must move towards the root through mass flow (most common) or diffusion. Diffusion if concentrations in the cell are low, active transport if concentrations in the cell are high.

Question 78

What are the 10 root types?

Answer 78

*Seminal and adventitious roots: 1st, 2nd, and 3rd order lateral roots *Feeder roots: fine, short-lived, acquire nutrients and water *Primary roots: growth by apical meristem *Secondary roots: mature, thicker ‘woody’ roots with periderm and additional vascular tissue *Coarse roots: long living, transport, and mechanical support *Rhizoids: not true roots, e.g. mosses *Aerial roots: common in epiphytes, adventitious roots that generally do not enter the soil, absorb water and minerals from the air or runoff from plants *Contractile roots: helps pull down to protect against high heat or low moisture, underside of bulbs, e.g. cactus *Cluster roots: form in plant families that don't have … symbioses, low-phosphorous soils *Prop roots: specialized adventitious roots that arise from the stem of certain plants and provide extra support.

Question 79

What is the rhizosphere?

Answer 79

The soil volume directly surrounding living plant roots, which is influence by root activities

Question 80

What is bulk soil?

Answer 80

The soil volume that is not directly influenced by the activities of plant roots.

Question 81

What is mycorrhizae?

Answer 81

Mutually beneficial symbiotic associations between plant roots and fungi ("fungus-root").

Question 82

What does the fungus gain from its association with plant roots in mycorrhizae?

Answer 82

Carbohydrates (sugars) produced by the plant during photosynthesis, which the fungus uses as an energy source. A supply of carbon fixed during photosynthesis.

Question 83

What does the plant gain from its association with fungi in mycorrhizae?

Answer 83

Enhanced uptake of nutrients (especially phosphorus, nitrogen, and micronutrients) and increased water absorption due to the extended fungal hyphal network.

Question 84

Name the two main types of mycorrhizae.

Answer 84

Arbuscular Mycorrhizae (AM) and Ectomycorrhizae (ECM).

Question 85

How many plant families have mycorrhiza symbioses?

Answer 85

92%

Question 86

What is a typical length of hyphae found in mycorrhizal associations?

Answer 86

Typical hyphal length = 2000 km m⁻².

Question 87

What is the typical diameter range of mycorrhizal hyphae?

Answer 87

1-10 µm diameter.

Question 88

How do mycorrhizal fungi enhance nutrient uptake for their plant partners?

Answer 88

They absorb nutrients beyond the root depletion zone, increasing the uptake of relatively immobile ions, e.g., phosphate.

Question 89

What are some evidence for the positive effects of mycorrhizal associations?

Answer 89

Ecosystem productivity, increased resistance to pathogens, tolerance to heavy metals, enhanced drought resistance, increased nodulation. (Any two or more of these are acceptable).

Question 90

What are rhizomorphs?

Answer 90

Rhizomorphs are root-like structures formed by some mycorrhizal fungi, and their primary function mentioned is transport.

Question 91

What is the role of foraging hyphae in mycorrhizal networks?

Answer 91

Foraging hyphae are responsible for nutrient acquisition from the soil.

Question 92

What is anastomosis?

Answer 92

Anastomosis is the fusion of hyphae from different fungi or genetically distinct individuals of the same fungus, leading to the formation of a Common Mycelial Network (CMN).