Soil Flashcards
What is soil fertility?
The ability of soil to sustain plant growth
What are good features of fertilie soil?
Good drainage so it doesn’t become waterlogged but so it retains enough for soil biota.
Well aerated
High DOM content which releases nutrients as it decomposes, also increases water retention.
PH 5.5-7
What are the macronutrients of soil?
Nitrates, phosphates, potassium
What are the micronutrients of soil?
boron, copper, iron, magnesium
What happens to toxic ions in soil?
Toxic ions like aluminium and heavy metals are adsorbed onto clay so they cannot dissolve in water
What do acidic soils do?
Increases leaching of plant nutrients and damages root cell membranes
What do alkaline soils do?
Make phosphates insoluble, which is not good because they already have low solubility.
What are the processes of soil biota?
Decomposers break down DOM by secreting enzymes
Detritivores finishing breaking up the process started by decomposers releasing nutrients to the soil
NF bacteria converting gaseous nitrogen to ammonium ions
Nitrifying bacteria oxidising ammonium ions to nitrites then nitrates
Mycorrhizal fungi aids phosphate uptake
What do detritivores include?
Worms, slugs, woodlice
What do decomposers include?
Bacteria and fungi
What do worms do to the soil?
Increase soil drainage and aeration by creating tunnels
What are the three types of soil erosion?
Rain splash
Wind
Surface runoff
How does ploughing and draining affect soil?
Makes soils more aerobic so increases the rate of NF, nitrification and decomposition of DOM
How do soil nutrient levels be increased or decreased?
Soil nutrient levels can be increased by adding inorganic/organic fertiliser so soils are more fertile.
Soil nutrient levels can be decrease by soil erosion, biomass removal or leaching which reduces soil fertility.
How does irrigation affect soil?
Irrigation will increase fertility where water is a limiting factor.
Sufficient water allows plants to keep their stomata open and continue gas exchange.
Water dissolves minerals to ions needed by plants
How does soil compaction affect soil?
Soil compaction by heavy machinery, or high livestock densities will reduce aeration of soils and make them more waterlogged.
Waterlogged soils increases denitrification and will increase surface runoff.
What do pH control do?
Ensures nutrients are soluble but not too easily leached
What is wind erosion and the problem it could cause?
Mainly in dry soils where there is no cohesion so soil isn’t held together so it blows away.
Unprotected soil will blow away.
Soil being blown can cover crops
What is water rain splash erosion?
When soil particles become dislodged by splashes from raindrops, the soil will be dispersed in all directions and will travel further downhill.
What is surface runoff erosion?
Occurs when the infiltration capacity if full/exceeded. The soil cannot hold anymore water so it runs off the soil.
When are landslides/slumping most likely to occur?
When soil becomes less stable after deforestation because roots are no longer holding soil together.
After heavy rain due to infiltration capacity being reached.
How can vegetation reduce the rate of soil erosion?
Vegetation acts as a windbreak reducing the kinetic energy that would carry soil particles away by wind erosion.
Vegetation cover/leaf litter reduces rain splash impact.
Humus helps bind soil particles.
Plant roots hold soil together.
Plants help increase infiltration so reduces runoff.
How does vegetation removal increase soil erosion?
Increases wind erosion due to less windbreak.
Increases rain splash erosion due to less leaf litter/vegetation cover.
Decreases infiltration storage and holds soil together less so more wind erosion and runoff erosion
How does ploughing increase soil erosion?
It breaks up the soil particles exposing them more
How does overgrazing increase soil erosion?
High livestock densities means vegetation will be eaten faster than it can grow this increases the exposure of soil to wind/rain so more erosion.
Root damage by hooves increases erosion
How does reduced soil biota increase soil erosion?
Less decomposers/detritivores so less DOM will be broken down leaving less nutrients in the soil so less vegetation grows.
Less decomposition so less humus, soil is therefore not held together
Less worms so less aeration of soil, less space for infiltration increases surface runoff.
How does soil compaction increase soil erosion?
Machinery/livestock causing compaction will decrease the amount of air spaces in the soil so less space for infiltration increases surface runoff.
What is accelerated soil erosion?
Where the rate of erosion is faster than the formation of soil
What happens to water flowing down steep slopes?
It has more kinetic energy because its flowing faster which means it can pick up more soil particles so more erosion
What can soil erosion lead to?
Reduced productivity as soil is less fertile.
Soil carried by wind may be deposited in rivers reducing the flow capacity so flooding is more likely.
Wind erosion increases atmospheric particles, making asthma worse.
Desertification
What are some methods to decrease soil disturbance and therefore soil erosion?
Long term crops so less soil disturbance.
Zero-tillage cultivation where seeds are drilled directly into the ground reducing soil disturbance.
What is contour ploughing?
Used to reduce soil erosion.
It is ploughing along contours at 90 degrees to a slope to reduce the kinetic energy and slow down water flow.
Water has lower kinetic energy so carries less soil particles
What is tied ridging?
Used to reduce soil erosion.
Used on almost flat land where it is divided in criss-crosses. They contain the water when it rains increases infiltration and reducing run off
What is terracing?
Used to reduce soil erosion.
On sloping land that is being cultivated soil is held in place by walls built along the contours.
This slows water flow so increases infiltration
What are rows of stones?
Used to reduce soil erosion.
Used on gentle gradients, the stones slow runoff so less erosion.
What are windbreaks?
Used to reduce soil erosion.
Growing crops to reduce wind erosion and velocity.
What is multicropping?
Growing more than one crop in a field to reduce exposure to wind when one is harvested.
How does increasing soil organic matter reduce soil erosion?
Organic matter as mulch will protect the soil from wind and the impact of rain drops.
As organic matter decomposes it produces humus which helps bind soil together.
What is the USLE used for?
To estimate soil loss rates
What is the USLE?
A= R x K x L x S x C x P
What do the letters in the USLE stand for?
A = soil loss
R = erosion type
K = change by adding DOM
L + S = length of field
C = crop management/plant
P = ploughing impact
What are the features of sandy soils and what do they allow?
Large pore spaces, so increased infiltration.
Nutrient ions do not absorb onto sand.
Easier root penetration
What are the features of clay soils and what do they allow?
Poorly drained/little pore spaces so less infiltration, more likely to be waterlogged.
Nutrient ions adsorb onto clay particles
List soil particles from smallest to biggest
Clay, silt, sand, gravel
List the method for soil colourimetry
2.5 cm3 soil to test tube
1cm3 barium sulfate to it
3.5cm3 distilled water and 10 drops of universal indicator
Bung tube and invert, leave for 15
Compare colour change to chart
Why are soil samples put in a sealed bag?
To prevent water loss by evaporation
What is the method to find soil water content?
Collect soil with auger
Place in bag to stop evaporation
Preweigh basin and soil sample
heat for 24hrs 100 degrees
reweigh then heat to constant mass
How do you calculate % water content?
Wet soil mass - dry soil mass / wet soil mass x 100
How do you collect a soil sample?
With an auger
What is the method to find soil organic matter content?
Preweigh crucible and DRY soil
Heat soil at 250 degrees with a bunsen burner until burnt
weigh crucible and find burnt soil mass, use this mass to calculate organic matter
How do you find the % organic matter content?
Dry soil mass - burnt soil mass/ dry soil mass x 100
Why should the temp be below 550 degress when finding the organic matter content?
Because minerals may break down and release CO2 which will affect the weight of burnt soil
What is soil bulk density?
Mass of dry soil per unit volume
How do u calculate soil bulk density?
mass of dry soil/ volume dry soil
to get vol of soil you have to use an auger
What are limitations of soil flooding?
Irritant in solution may not reach deep worms
Worms may move further down or to the side instead of out of the soil
Worm too slow/ dont move
Can harm worms
