The Physical Environment (AS); Soil (Complete) Flashcards

1
Q

What is soil essential for?

A

Plant growth in natural ecosystems & agroecosystems

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2
Q

What is soil fertility?

A

The ability of soil to sustain plant growth

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3
Q

How is water content a feature of fertile soil?

A

-Water → essential for all organisms living in soil including plants
-Fertile soil allows good drainage so doesn’t become water logged but still retains enough water for soil biota survival
-Plant nutrients = absorbed in ionic form, dissolved in water

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4
Q

How are soluble materials a feature of fertile soil?

A

-Have macronutrients like nitrogen, phosphorus & potassium, present in ionic form ; mainly nitrates, phosphates & potassium ions
-Have micronutrients like boron, cobalt, copper, iron, manganese & magnesium
-Toxin ions like aluminium & heavy metals are absorbed → surface of mineral particles (usually clay); so can’t dissolve in water & harm soil organisms

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5
Q

How is air content a feature of fertile soil?

A

Most living organisms in soil & many processes increasing fertility = aerobic → well aerated soils likely to be more fertile

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6
Q

How does dead organic matter contribute to soil fertility?

A

-Usually have a high dead organic matter content → releases plant nutrients as decomposes
-Increases water retention & provides food for soil biota

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7
Q

How is pH a feature of fertile soil?

A

-Usually in range of pH 5. 5- 7.0 → range of tolerance for most plants, soil biota
-Acidic soils can ↑ leaching of plant nutrients & damage root cell membranes
-Alkaline conditions; phosphates become insoluble

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8
Q

How do soil biota contribute to the fertility of soil?

A

Living organisms = involved in many processes affecting soil fertility;
-Detritivores like beetle larvae, worms break up dead organic matter, release nutrients → soil. Also ↑ soil drainage & aeration by making tunnels in soil
-Decomposers like fungi break down dead organic matter; secrete digestive enzymes + rely on detritivores to physically break up dead organic matter, increase its surface area
-Nitrogen fixing bacteria convert gaseous nitrogen into ammonium ions
-Nitrifying bacteria oxidise ammonium ions → nitrite ions → nitrate ions
-Mycorrhizal fungi form symbiotic relationships w/ plant roots, aid phosphate uptake by plants

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9
Q

What is soil texture controlled by and what does this involve?

A

Proportions of different size categories of mineral particles present in soil;
- Clay; <0.002 mm diameter
-Silt; 0.002 - 0.02 mm diameter
-Sand; 0.02- 2.0 mm diameter

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10
Q

How do drainage rates compare in sandy and clay soils?

A

-Larger pore spaces of sandy soils allows rapid drainage → reduces water content, increases aeration
-Clay soils = poorly drained

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11
Q

How does capillary action compare in sandy and clay soils?

A

-Tiny pore spaces between clay particles allow underground water to rise towards surface
-No capillary rise of water in sandy soils

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12
Q

How does aeration compare in sandy and clay soils?

A

-Pore spaces in well-drained sandy soils; filled w/ air
-clay soils; more likely to be waterlogged w/ low aeration rate

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13
Q

How does nutrient retention compare in sandy and clay soils?

A

Nutrient ions absorb easily onto clay particles but not onto sand particles

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14
Q

How does thermal capacity differ in sandy and clay soils?

A

-High water content of clay soils; high thermal capacity, warm up & cool down slowly
-Sandy soils; low thermal capacity, warm up more rapidly after cold weather

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15
Q

How does root penetration differ in sandy and clay soils?

A

-Clay particles = held together by capillary water on particle surfaces; harder for plant roots to force way between soil particles
-Sandy soils = root penetration easier

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16
Q

How does ease of cultivation compare in sandy and clay soils?

A

Lack of adhesion between particles in sandy soils; easier to cultivate than clay soils

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17
Q

What is the composition of loam soils and why is this advantageous?

A

-Fairly even mix of sand, silt & clay (approx 40:40:20)
-Ideal mix of properties for cultivating most crops; good drainage,water retention, high nutrient content

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18
Q

What is the structure of soil and its different types?

A

-Soil particles form aggregates called peds
-Particles = bound together by polysaccharide gums made by decomposition, by fungal hyphae, by roots, by action of soil biota & hygroscopic clay particles
-Ped type affects soil properties & fertility. Crumb peds= small & round. Produce good drainage, aeration & easy root penetration → improve soil fertility. Platy peds= large & flat. Reduce drainage, aeration & root penetration → less fertile soils

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19
Q

How does depth affect soil?

A

-Deeper soils—> less likely to become waterlogged/dry out rapidly
-Can also aid good root anchorage

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20
Q

Humans affecting soil fertility; aeration by ploughing & drainage?

A

Ploughing + drainage makes soils more aerobic= increases rates of N fixing, nitrification & decomposition of dead organic matter

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21
Q

Humans affecting soil fertility; soil nutrient levels?

A

-Farmers increase soil nutrient levels by adding inorganic fertilisers, organic matter, supporting natural processes increasing nutrient levels like bacterial nitrogen fixation
-Farming can also deplete soil nutrient levels due to soil erosion, biomass removal, inhibiting natural processes increasing nutrient levels/increasing leaching of dissolved nutrients

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22
Q

Humans affecting soil fertility; irrigation?

A

-Increases fertility of soil where water= limiting factor on growth
-Sufficient water allows plants to keep stomata open, continue gaseous exchange when soil would otherwise be dry
-Water dissolves nutrients, can be absorbed by plants in ionic form

23
Q

Humans affecting soil fertility; soil compaction?

A

-Excessive use of heavy machinery/high livestock densities—> soil becomes compacted
-Aeration is reduced & waterlogging is more likely; especially when soil is wet

24
Q

Humans affecting soil fertility; pH?

A

Controlling soil pH helps ensure nutrients= soluble but not too easily leached

25
How does soil erosion occur naturally and what is the rate of this?
-Soil particles are removed by wind/water -Soil erosion rate is likely to equal/less than rate of soil formation
26
Types of soil erosion; what is wind erosion and why is it an issue?
-Soil= dry, low clay content—> likely to become loose w/ little cohesion between particles holding soil together -If it’s windy, soil is unprotected; may blow away -Can cause issues where soil is deposited as may cover crops/land in urban areas
27
Types of soil erosion; how is water erosion increased?
Steeper gradients
28
Types of soil erosion; what is rain splash erosion and why is it an issue?
-A type of water erosion -Soil particles dislodged by splash of a raindrop. Soil particles are dispersed in all directions, those going downhill= likely to travel further -Overtime, can cause downhill movements of large soil amounts
29
Types of soil erosion; what is surface runoff erosion and how is it an issue?
-Caused by surface runoff when infiltration capacity of soil has been exceeded -Can occur when rainfall= heavy/prolonged, or soil is relatively impermeable so more water flows over ground surface
30
Types of soil erosion; when do slumping and landslides occur and how is this an issue?
-When soil on slopes becomes very wet, increased mass & lubrication of water—> downward movement of large soil amounts more likely -Often occurs when deep soil on steep slopes becomes less stable post deforestation -As roots that held soil together decompose, soil= held together less strongly & landslides following rain are more likely
31
How does vegetation reduce the rate of soil erosion?
-Acts as a natural windbreak, reducing wind velocity & therefore kinetic energy carrying away soil particles -Vegetation cover & leaf litter reduce impact of raindrops on soil surface—> soil particles less likely to be dislodged -Soil organic matter, incl colloidal material humus, helps bind soil particles together -Plant roots hold soil together -Plants help increase infiltration of water into soil—> reduces rate of runoff & water erosion
32
Humans activities increasing rate of soil erosion; vegetation removal?
Removes protection from erosion
33
Humans activities increasing rate of soil erosion; ploughing vulnerable soils?
Breaks up soil structure, exposing soil particles to erosion by water/wind
34
Humans activities increasing rate of soil erosion; overgrazing?
-If livestock density= too high, vegetation will be eaten faster than it can grow, increasing exposure of soil & risk of erosion -Disturbance & root damage by hooves increases erosion risk
35
Humans activities increasing rate of soil erosion; reduced soil biota?
-Ploughing, reducing soil organic matter & use of agrochemicals can reduce # of living organisms in soil, which play an important part in reducing soil erosion; -Detritivores & decomposers break down dead organic matter, releasing plant nutrients—> may increase vegetation cover -Decomposition produces humus—> increases adhesion between soil particles -Worms aerate soil, increasing drainage rate, infiltration capacity of soil
36
Humans activities increasing rate of soil erosion; soil compaction?
-Use of heavy machinery, high livestock densities, reduction in soil detritivores= more likely soil will be compacted -This has smaller interstitial spaces, reduces infiltration rate so more likely rainfall will produce surface runoff & erosion
37
Humans activities increasing rate of soil erosion; cultivating steep slopes?
-Surface runoff water flows more rapidly down steeper slopes, has more kinetic energy to pick up and carry soil particles -Cultivating w/ techniques disturbing soil (eg ploughing) adds to erosion risk
38
Effects of accelerated soil erosion; reduced productivity?
-Soil eroded → often most fertile topsoil lost -Remaining soil may=less fertile → reduced plant growth + smaller harvests -Erosions → leave shallower soil, root penetration may = more difficult
39
Effects of accelerated soil erosion; sedimentation in rivers & reservoirs?
-Soil particles carried → river may be deposited if water slows down, has less kinetic energy -Can occur where river naturally slows down in reservoirs/on coastlines if suspended soils reach sea -Soil that sediments in a river ↓ flow capacity, so river = more likely to overflow & cause flooding post heavy rain
40
Effects of accelerated soil erosion; Increased atmospheric particulates?
-Wind erosion ↑ level of atmospheric particulates -Can make health problems like asthma worse
41
Effects of accelerated soil erosion; Desertification?
-Soil erosion → important part of combination of processes causing expansion of deserts -Makes it mare difficult for vegetation to grow, contributes to further soil erosion, reduced rainfall
42
How do long-term crops reduce soil erosion?
-Growth of crops not requiring frequent replanting & soil disturbance =↓ erosion rate -Eg permanent grassland & tree crops like fruit, tea, coffee
43
How does zero-tillage cultivation reduce soil erosion?
-Cultivation minimizing soil disturbance → reduces risk of soil erosion -Direct drilling of seeds into ground = less disturbing than ploughing/ sowing
44
How does contour ploughing reduce soil erosion?
-Ploughing up & down slope → gulleys,↑ velocity of runoff + cause more rapid erosion -Ploughing along contacts at 90° to slope ↓ erosion as water flow is stopped by ploughed furrows loses kinetic energy → can't carry soil particles -W/ slower flow rate → soil particles deposited in furrow. Works well unless rainfall is so heavy furrows overflow
45
What is tied ridging and how does it reduce soil erosion?
-Used on almost flat land -Field divided w/ criss-cross of intersecting ridges -Ridges retain water when it rains,↑ infiltration &↓ runoff that may have caused erosion
46
What is terracing and how does it reduce soil erosion?
-Where sloping land = cultivated, series of narrow fields are created w/ soil held in place by retaining walls built along contours -Water flowing over walls flows quickly, but slows down as flows across fields -Much of the water may infiltrate into soil
47
How do rows of stones reduce soil erosion?
-If gradient = gentle, rows of stones laid along contours can slow runoff &↓ erosion rate -Any disturbed soil is deposited behind stone rows
48
What are windbreaks and how do they reduce soil erosion?
-Growing crop ↓ velocity of wind,↓ wind erosion but field will be exposed if plants are removed when crop is harvested -Protection from wind is maintained if there's hedgerows / rows of trees around field -Hedgerow → reduces wind velocity for distance up to 30m its height
49
How can multicropping reduce soil erosion?
-Growing 1> crop in a field at same time can ↓ exposure to wind erosion if are harvested & re-sown at diff times b/c there's always a crop in the field protecting the soil -Works most easily where farming uses human labour, not machinery -If work is done w/ machinery, wider strips of diff crops may be cultivated in 'strip cropping'; strips more effective if arranged at 90° to prevailing wind direction
50
How can increasing soil organic matter reduce soil erosion?
-Any method retaining/adding organic matter will ↓ risk of erosion -Organic matter an soil surface like mulch protects soil from wind & impact of rain drops -As organic matter decomposes it makes humus (colloidal material) , which helps soil particles adhere to each other
51
How can livestock management reduce soil erosion?
-Stocking density can be controlled to ↓ soil damage, eg trampling damage -Livestock movement can be controlled; eg ↓ access to riverbanks where trampling = more likely to cause erosion into river -Livestock may be removed at high-risk times, eg post heavy rain
52
What does The Universal Soil Loss Equation (USLE) estimate and assess?
-Estimates soil loss rates & the rate of soil erosion for particular local conditions and cultivation practices -Assesses impact of changes in farming techniques
53
What is the USLE formula and what does it represent?
A= R x K x L x S x C x P A= Rate of soil erosion (annual soil loss) R= Rainfall erosivity factor (measure of the potential ability of soil to be eroded by rain) K= Soil erodibility factor (susceptibility of soil particles to detachment by rainfall and runoff) L= Slope length factor (effect of slope length) S= Slope gradient factor (steepness of slope) C= Cropping management factor (impact of vegetation) P= Erosion control factor (effect of type of ploughing)