Flashcards
Soils
Flashcards do conjunto (54)
- 1What are soils made up of?Inorganic Materials - sands/ silts/ clays/ minerals
Organic Materials - Alive and dead
Air
Water - 2What are the roles of soils?- A medium for plant growth - support, nutrients and air
- Reservoir of water - influences quantities elsewhere
- For filtering and transforming minerals added to the soil
- Recycling dead organic matter into nutrients
- Providing a habitat for organisms
- Providing raw materials (sands/clays/minerals)
- As foundations for buildings
- Protecting cultural heritages by preservation - 3What are the 4 major components of soil?1. Inorganic fraction (mineral fraction)
2. Organic matter
3. Water
4. Air - 4Describe the characteristical splitting of topsoil1. Half of it contains solid organic and inorganic material
2. The other half contains voids (pores) filled with air and water around more solid soil
(Agricultural soils can contain less than 10% organic matter and are considered mineral soils) - 5Explain the mineral particle property of soil- The predominant fraction of most soils
- Derived from weathering of parent material (physically and chemically)
- Larger - boulders, stones, gravel, coarse sands
- Smaller single minerals - 6What are primary minerals?Minerals that have seen very little change since they were formed from magma (quartz, feldspars and micas)
- 7What are secondary minerals?Breakdown particles of the less resistant primary minerals (clays, iron/aluminium oxides)
- 8What is organic soil matter made of?1. Litter - decaying matter
2. Humus - a more resistant organic matter
3. Soil biomass - living organisms and plant roots - 9What is meant by mineralisation?When decomposition is occurring progressively by micro-organisms and nutrients are being released (nitrogen/phosphorous/sulphur)
- 10What is the average content of organic matter of soils?-Averages around 2-6% by volume
-In arid climates it can be 0.5-2%
-In waterlogged conditions it can be higher as it takes longer to breakdown - as much as 65-90% and its then known as peat (can be a few metres deep)
-Balance between inputs and outputs determines the organic matter content - 11Why is soil organic matter important?1. The main source of food for soil organisms
2. Binds mineral particles together = stabilisation = less erosion
3. Improves water holding capacities
4. Improves porosity + aeration aiding plant growth
5. Influence on fertility through nutrients - 12What is meant by the soil solution?Soil water containing dissolved organic and inorganic substances, including all the ions
- 13What is an important function of soil solution?-Ensure the continued supply of anions and cations to the roots
-Acts as the main agent for translocation - 14How is water held in the soil?*By the attraction of water molecules to each other and soil particles which is then greater than any gravitational forces
- 15What are the three states that water can exist in in soil?1. SATURATED - All soil pores are filled with water
2. GRAVITATIONAL WATER - Water is drained from the larger pores and replaced by air (when all of it has drained, the soil is at FIELD CAPACITY)
3. CAPILLARY WATER - The smaller pores retaining water against gravitational forces - this makes for the majority of water available for plant uptake (moves from zones of higher potential (wet) to lower (dry))
4. Hygroscopic water - Held as a tight film around individual soil particles - water is unavailable to plants as attraction is too great - 16What is the wilting point?The point where at hygroscopic water the plant can't withdraw any water at all from the tightly held soil
- 17What is meant by available water?The amount of water in the soil between field capacity and wilting point
- 18What effects the amount of water held in each state?1. Soil texture -small (clay type) particles hold more water (S.A:Vol), but this is mainly hygroscopic as its contained in very small pores
2. Soil structure - Nature and abundance of pores relates to how much water is drained
3. Organic matter content - Increases moisture holding content and influences structure - 19What is soil air?Any pores in the soil not filled with water
- 20What is meant by aeration?Because of the living element of soils, oxygen and carbon dioxide exchanges have to exist in the soil - this ventilation is known as aeration
- 21What is aeration affected by?1. Pore size distribution
2. Pore continuity
3. Soil water content
4. Rate of oxygen consumption by respiring organisms - 22What is the composition of soil air?*Generally has a higher moisture and carbon dioxide content (can be several hundreds of times higher) and lower oxygen contents than in the atmosphere
*It constantly changes with diurnal and seasonal variations by differences in biological activity
*Is different throughout soil layers - 23What is the soil profile?*A vertical section from ground surface to parent material
*Made of horizontal layers - soil horizons made by the translocations of materials and water movement - 24What is meant by eluviation?The removal of solid or dissolved material from one horizon
- 25What is meant by illuviation?Deposition of materials into a horizon
- 26Describe the horizons cross sectionO - Surface layer of accumulated organic matter
A - Mineral horizon - contains a mixture of mineral and organic (humus) material and is dark in colour
E - Elluvial horizon - zone of deposition (clay/iron/aluminium) lighter than A and B
B - illuvial horizon - zone of accumulation (iron oxides will give it a reddish colour)
C - Regolith - unconsolidated weathered parent material
R - the unweathered bedrock - 27What is the solum?A, E and B horizons
- Where soil forming processes are active and plant/animal life is - 28What is topsoil?Upper portion of the soil - A horizon (most important part for plant growth)
- 29What is subsoil?Soil below the topsoil (plough depths) usually the B horizon
- 30What is pedogenesis?*The process of soil formation
*Over hundreds and thousands of years - 31What are the main inputs for soil formation?*Starts with the parent materials breakdown
*Surface accumulation (particularly from organic matter) builds it up
*Other inputs include solutes and particles carried by wind/rain, energy from the sun and atmospheric gases - 32What are the main outputs for soils?*Wind and water erosion
*Leaching - Removal of soil minerals in solution (especially at times of high rainfall/ rapid drainage). Either takes them further into the soil or out of it completely (often indicated by acidity)
*Loss of gases
*Uptake of solutes by plants - 33How are organic and inorganic components mixed together?1. Carried by animals, roots, microbes
2. Freeze/ thaw
3. Anthropogenic - ploughing
4. Chemical and biological processes - decaying organic components/ dissolved minerals - 34How does translocations of particles occur?- Gradients of water potential
- Chemical concentrations within soil pores
- Where rainfall exceeds evapotranspiration then net water movement is down through soil - 35What is an argillic horizon?- Horizons characterised by clay accumulation
- Happens when, in free draining soils, clay particles are carried by percolating water down and create films around aggregate surfaces or in pores around stones - 36What are luvisols?Soils typically been affected by clay eluvation
- 37What are podzols and how are they formed?- Podzolization occurs where there is extreme leaching and translocation of material
- Organic compounds/iron and aluminium horizons taken by percolated water from E to B
- Happens in freely drained sites (under forests/ heaths)
- Creates a podzol - soil with O horizon, leached E and high iron/aluminium content in B
- Not agriculturally productive as are acidic and free drainage from leaching takes fertalisers - 38What is gleying?Where the ferric (Fe3+ compound) to the more mobile ferrous (Fe2+ compound) occurs through waterlogged ground by microorganisms
- This soil looses brown/red colour of ferric oxide and becomes blue/grey - 39What is meant by lateralisation?Occuring in tropical/subtropical soils, where high temps and heavy rain results in leaching
Less base cations in horizons (Ca/Mg/K/Na)
More silica/aluminium and iron oxides in horizons
(Where evapotranspiration exceeds rainfall, water is drawn to the soil surface and salts then left on surface from evaporation) - 40What factors can influence soil formtion?1. Climate
2. Parental Material
3.Relief
4. Organisms
5. Time
6. Combined influences - 41How does climate affect soil formation?- Arguably the most influential factor
- Determines the moisture and temperature regimes under which the soil develops
- Rainwater not only will effect hydrological processes within the soil, but on weathering and leaching
- Amount that percolates and the speed at which it does are also very important (depends on amount of precipitation and rate of evaporation)
- Topography and permeability are also important factors
- Percolating water will determine soil horizons and influences soil depth
- Temperature influences the rate of soil formation via mineral weathering and organic material decomposition
- For every 10oC temp rise, chemical processes increase by 2/3, biological processes double (until 30-35oC) and evaporation increases
-Soils are influenced by microclimates that are related to altitude and aspect - 42How does the parent material affect soil formation?* Soils can develop on weathered surfaces of exposed consolidated in situ rocks surfaces or unconsolidated superficial material that's been transported by gravity/water/ice/wind
*Parent material --> weathered material --> soil processes
*Rock types will influence the rate of weathering through mineralogical composition and S.A of rock exposed
*Minerals that crystallise first form under much higher temperatures and are more susceptible to weathering
*The weathering products of chalk and limestone are very soluble - soil depths are shallow (particularly on steeper slopes). On foots of slopes, soils are deeper and are well drained and base ion rich - 43How does the relief affect soil formation?- Relief relates to altitude/ slope and aspect and can hasten/ delay climatic influences
- Slope is important - steeper slopes reduce the amount of water infiltrating and percolating and allow for increased erosion of surface layers
- Soils on steeper slopes are then thin, coarse and more poorly developed
- On slopes of less permeable parent material, surface water logging causes gleying on flat ground
- Aspect affects solar energy received at ground surface - (In northern hemisphere, south facing slopes receive more and are warmer - have generally lower moisture) this means less vegetation = less organic matter
- Altitude affects by temperature declining with altitude - leads to reduction of biological activity, slowing decomposition of organic matter (accumulation of thick organic horizons at surface and eventual peat formaiton) - 44What is meant by catena?This is where there is no change in geology along the slope and soil differences are brought about by drainage conditions, differential transport, eroded material and the leaching, translocation and redeposition of chemical constituents
- 45How do organisms affect soil formation?- Vegetation takes out water and nutrients (in totally natural conditions this would go back into the soil as litter)
- The type of vegetation will determine type and amount of litter returned
- Vegetation would usually protect soil from water and wind erosion (interception / decreasing velocity of runoff / binding soil particles / improve structure and porosity
- Some animals will turn and areate soils as they burrow
- Earth worms have been found to increase infiltration rate of fine soils and contribute to increasing stability of soil structure by intermixing organic and mineral particles
- Saprotrophic bacterias play role in breakdown
- Humus as an end product will then influence soil formation through manipulation of vegetation - 46How does time affect soil formation?- Soil is continually forming from parent material
- Soil genesis of a 30cm layer takes from 1000 - 10000 years
- During this time properties continually change
- When rate of change of horizons/ depth and degree of differentiation is negligible the soil is said to be stable
- Most soils haven't developed under a single set of environmental factors (would have undergone successive waves of pedogenesis) - glacials/interglacials/ sea level change/ erosion/ deposition - 47What is meant by soil colour?- Has little effect on the soil itself
- Use it to determine the nature of soil properties (organic material content/ aeration/ drainage characteristics)
- Determines which horizon and horizon layer differentiations
- Black/ dark brown soils = high in organic matter
- Drainage characteristics determined by the iron content (well drained = oxidised iron = red/yellow
- In waterlogged soils - iron reduced (anaerobic conditions) grey/blue colour - 48Describe the Munsell colour chart- A standard system for describing colour of soil
- 3 measures determine colour
1. HUE = dominant colour of the pure spectrum
2. VALUE = degree of dark/lightness (0=black)
3. CHROMA = purity or strength of the colour
Then the final colour is described as a letter numerical code - 49What is meant by soil texture?* Mineral particles varying in size
1. BOULDERS - <600mm
2. STONES - <2 mm
3. SAND/ SILT/ CLAY - <2micrometres - often referred to as fine earth - separate from larger soil particles by passing through a sieve
* Surface area in different soil types differs and then this leads to different water holding capacities/ CEC (cation exchange capacity) and rate of mineral weathering
*Soils will very rarely be composed of a single particle caste
*Texture refers to the relative ratios of sand, silt and clay
*11 main textural classes - 50What is meant by soil structure?- Soil particles will adhere to each other, forming aggregates or peds
- Soil structure = shape, size and distinctiveness (grade) of the peds
- Each ped separates from another by voids/ natural planes of weakness
- 4 principal areas
1. BLOCKY - common in B horizon. Peds in same order of magnitude, with flattened surfaces from adjacent peds
2. SPHERODIAL- A horizon. Peds equidimensional. 1. GRANULAR - non- porous 2. CRUMB - porous. Organic matter and roots helps their development
3. PLATY - E horizon. Compacted clay soils. Predominantly horizontal cleavage/ short vertical axis
4. PRISMATIC - B horizon in clayey soils. Peds with vertical axis longer than horizontal - form vertical columns often with rounded tops - 51What terms describe the grade of soils?1. Structureless (no peds)
2. Weak (indistinct peds - breaks easily into unaggregated material)
3. Moderate (well formed peds/ little unaggregated material)
4. Strong (distinct peds/ aggregated even if disturbed) - 52What factors form stable peds?1. FREEZE-THAW / WET-DRY / SHRINK-SWELL processes, especially in the top layers. Help mould shape into peds and change volume of soil, moving particles throughout the profile
2. BURROWING ANIMALS - mixing of organic particles - formation of stable organo-mineral complexes. Produce macropores and channels. roots can also secret polysaccharides that then bind soils. Fungal hyphae hold mineral and organics - 53What does ploughing do to soil structure?- Weakening the ped and aggregate structures
- Hevy farm machinery can also compact topsoils - 54—
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- FlashCards sobre Soils, criado por ph133132 em 02-11-2015.
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