Soil Science Exam

What is soil?

Soil is an organic mineral mix in which four distinct spheres interface. Namely the:

• Lithosphere

• Biosphere

• Hydrosphere

• Atmosphere

the intersection of those spheres is pedosphere - in other words: soil 

Describe 5 soil functions

Soil functions: 

• purification system for water

• modifier of the atmosphere 

• system for water supply  

• engineering medium 

• serves as habitat for soil organisms 

• recycles nutrients and organic matter 

• medium for plant growth 

Name Horizons> Name main properties for Horizons

• O - not present in all soils. feature of mostly forest soils in which a dense layer of organic material builds up on the surface of the topsoil 

• A - organic matter and minerals are intimately mixed

• E - not present in all soils - mostly in forest soils with a lot of downward movement of water. zone in which minerals are leached resulting in a distinctive “bleached layer” consisting mostly of quartz minerals  

• B - zone of accumulation. its lower in organic content then A horizon. contains more of the minerals leached from upper horizons. contains less pore space being usually dominated by micropores. 

• C - consists of unconsolidated parent material which has been partly weathered by plant roots, enzymes and so on

• Bedrock ® - consolidated parent material 
  

Soil-forming factors

Soil-forming factors: all interdependent!

a) Parent material

b) Climate

c) Biota

d) Topography

e) Time

The 4 Soil Forming Processes. AND EXAMPLES

- Additions -> dust, fertilizer, manure, OM from litter/roots
- Losses -> leaching, surface erosion

- Translocations -> earthworm mixing of OM, water transport of OM  

- Transformations -> humification, chemical weathering, synthesis (clays formed from primary minerals)

Know how to read the texture triangle

What are the sizes of clay, silt and sand particles?

Clay (smallest) - >0.002 millimeters in diameter 

Silt - 0.002 mm to 0.05 mm in diameter 

Sand - 2mm to 0.05 mm in diameter

SOM: why is it important?

- Nutrient release: vital to cycling of C, N, S, P 
- Soil aggregate stabilisation  

- Cation exchange capacity 
- Water holding capacity 
- Inactivation of pollutants 
- Long-term C storage (climate change) 
- Soil temperature adjustment 
- Habitat and energy source for soil microbes

Why are soil colloids important?

- Negative and positive charges 
- Attraction and repulsion of ions 
- Attraction of water molecules 
- Adsorption of cations (Al3+, Ca2+, Mg2+, K+, Na+, H+) 
- Constant exchange & release of plant nutrients 
- Equilibrium of soil solution and exchange sites 
- Fixation of pollutants

Which are the important steps of cultivation on arable land?

1. Primary tillage and reconsolidation

2. Secondary tillage or seedbed preparation

3. Seeding/planting

4. Plant protection/weeding/fertilizer application/irrigation

5. Harvest

What are the aims of the different cultivation steps?

- create a good soil structure (granular, crumb)

- remove unwanted plants by burying, cutting, ripping out and squeezing

- leveling soil surface

- alter surface to enhance infiltration of water

- stimulate organic matter breakdown to release nutrients (mineralisation)

- place seeds and fertilizer

- increasing trafficability of soil

How do these steps influence soil properties?

- consolidation (reduction of soil volume due to loss of macropores < 30 µm) 
- plough pans from subsoil compaction reducing air/water storage = hampered growth of deep-rooted crops e.g. corn 
-coalescence = fine particles deposited between aggregates after tillage in dry conditions 
- slaking = structural collapse when dry aggregates wetted rapidly 
- sealing = fine particles enter macropores, reduce infiltration
- soil erosion by water and wind
- loss of soil organic matter by decomposition

Earthworms: name the main groups and their habitats/behavior. . Habitat and characteristics of earthworms (anecic, epigei, endogeic) and how they live.

epigeic - leaf litter compost, pigmented
endogeic - top soil, subsoil (unpigmented)

anecic - deep burrowing (unpigmented, part of the tail is colored)  

Why is the size of the soil microbial biomass important?

-> Soil microbial biomass is an important pool of nutrients.

- “Early warning system”, e.g. change of organic matter content;

- Microbial biomass is closely related to the soil organic matter content

- Indicator of soil quality (size, metabolism)

- Biological buffer against environmental stress (resilience, self regulation, functional diversity, functional redundancy)

- Biocatalyst: degradation of xenobiotics (resilience)

- Suppressive soils

- Weathering of soil minerals

- Altering the redox properties of the soil

- Humification organic matter enrichment

- N2-fixation

Know the diagram: Different soil water contents in soils of different textural classes

Define soil texture and soil structure

Soil texture - relative amount of soil particles of different sizes (salt, silt, clay) forming the soil mineral matter

Soil structure - describes how those particles are arranged, soil structure considers the pore space as well as organic matter.

Is there soil on the moon? Why?

No, there is no soil on the moon because the atmosphere, hydrosphere and biosphere is not present and they are all necessary constituents of the pedosphere.

What Does the C/N ratio mean?

a ratio of the mass of carbon to the mass of nitrogen in organic residues.

It can, amongst other things, be used in analyzing sediments and soil including soil organic matter

What processes influence C and OM pools?

Agricultural practices like tilling will quickly start to influence SOM reducing the amount of plant residues, active OM, slow OM and will slowly start to degrade passive OM pool.

Overall loss of total SOM with the SOM being eventually dominated by the passive OM and therefore a low C/N ratio.

SOM content can also be improved by eg. OM management practices like:

- reduced till

- no till

- cover cropping

- mulching

- putting the land back into native vegetation

Explain the steps of Leguminous N2>fixation with the rhizobia bacteria. Which factors influence that process?

Steps:

1. Rhizobia in soil contact legume roots

2. Infection of root hairs → nodule formation

3. Rhizobia fix N₂ → NH₃ inside nodules

4. Plant uses NH₃ for growth; supplies bacteria with sugars

5. Active nodules = pink (leghemoglobin); old = gray/green

Key Factors:

• Rhizobia strain + legume type

• Soil nutrients (P, K, micronutrients)

• Water, temp, O₂ balance

• Low soil N (high N suppresses fixation)

• Plant health, photosynthesis

Name the Pathways of:organic nitrogen, ammonium and nitrate

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How can you measure the phosphatase activity and what does it indicate?

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What types of classification and thresholds are there for soil salinity?

Saline, Sodic, …know ESP, EC, ph

EC = electrical conductivity (dS/m = decisiemens/meter), influenced by salt content (chlorides and sulfates of Ca, Mg, Na & K)

ESP = exchangeable sodium percentage (%)

SAR = sodium adsorption ratio

TDS = total dissolved solids; mass of dissolved salts per unit of volume soil water

CEC = cation exchange capacity (cmolc/kg soil)

How can these soil problems be tackled?

- Alkalinity

- Salinity

- Sodicity

Counteracting:

Salinity:

- Improve irrigation to leach excess salts below root zone (~80 % of salts can be removed by a volume of water passing through the same volume of soil)

- Improve drainage to lower water table -> reduce upward movement of water and salt

- Apply organic matter Utilize salt-tolerant crops

Sodicity:

Removing sodium from the exchange complex and soil profile as Na2SO4

- Application of gypsum, sulphur or sulphuric acid and excess water (leaching of salts)

2NaHCO3 + CaSO4 CaCO3 + Na2SO4 + CO2 + H2O Na2CO3 + CaSO4 CaCO3 + Na2SO4

Alkalinity

- Lowering the pH in the rhizosphere application of sulphur, sulphates (Fe, Ca) or sulphuric acid

Create a soil footprint 8P. How can we measure it? Which soil properties are relevant?

texture

pH

OM

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What is the difference between a resilient soil in comparison to a resistant soil? Give an example for a resilient soil( soil A) and a resistant soil (soil B)

Soil resistance = capacity of a soil to resist change when confronted with a disturbance e.g. compaction or nutrient depletion

e.g. plant uptake of K replenished more easily from fine textured than sandy soil = much better resistance

Soil resilience = the capacity of a soil to recover its structural and functional integrity after a disturbance

name functions of OM in soil

- Nutrient release, especially N

- Soil aggregate stabilization

- Cation exchange capacity

- Water holding capacity

- Inactivation of pollutants

- Long-term C storage

What produces the OM and C pool?

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name OM management tools

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Pesticides: How do they get into the soil? Environmental Effects? Alternatives to pesticides?

a) Soil has key role in a pesticide´s dispersal:

• many pesticides are soil-applied

• wider range enters soil due to rain-wash from leaves

• incorporation of pesticide-treated plant residues into soil

b) Alternatives to pesticide use:

- Integrated Pest Management:

• redesign agricultural system to favour pest predators, disadvantage pests e.g. crop rotation, ground cover and pest-resistant cultivars

- Natural pesticides:

• Nicotine kills sap-sucking insects

• Eugenol herbicide extracted from oil of cloves

- Biological strategies:

• aphid parasites attracted by clover and sunflower

• decoy plants e.g. mustard attracts cabbage butterflies

• use of hormones/pheromones to remove insects from crops e.g. fruit fly

c) Environmental effects:

residues may spread in environment and enter food chain

„broad spectrum“ chemicals may kill beneficial organisms (e.g. mycorrhizal fungi or N-fixation bacteria)

harm to pests´ natural predators

How can plants help to clean soils from toxins.2 different processes

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Fill out the flow diagram with the names of different parent material deposits

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Fill out the flow diagram with the names of different parent material deposits

water logging results in upward movement of salts <only info

Fate of org N,

Fate of NH4

Fate of nitrate

Fate of:

a) Organic nitrogen:

1. Immobilization by soil microorganisms

2. Removal by plant uptake (amino acids)

3. Loss to groundwater by leaching

4. Mineralisation by soil microorganisms

Loss by runoff and erosion

b) NH4 +

1. Immobilization by soil microorganisms

2. Removal by plant uptake

3. Fixation to clay minerals

4. Volatilisation as gaseous NH3

5. Oxidation to nitrite and nitrate (nitrification)

Loss by runoff and erosion

c) NO3 -

1. Immobilization by soil microorganisms

2. Removal by plant uptake

3. Loss to ground-water by leaching

4. Dissimilatory nitrate reduction (to NH4 +)

5. Volatilisation as NOx, N2O, N2 (denitrification)

Which is the FAO classification of soil types?

The Food and Agriculture Organization of the United Nations (FAO) -

diagnostic properties and diagnostic horizons based on soil formation

eg.

Ferralsols

Acrisols

Lixisols

Luvisols

Nitisols

Arenosols

Calcisols

Solonetz

Gleysols

Fluvisols

Which properties define dry regions?

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Soil Types in tropical regions ­which is one? Vertisol, Ultisol, Oxisol, etc.

1. • Kaolinitic soil - Account for more than 70% of all tropical soils
   - A-horizon often sand to sandy loam
   - B-horizon clayey with kaolinite > 90% of clay minerals
   - Highly weathered, low CEC

2. . Oxidic soils - Second most widespread soils
   - Strongly weathered red and yellowish, fine-textured soils
   - Kaolinite and Fe-/Al-oxides

3. Allophanic soils
   - Dark-coloured young soils derived from volcanic ash
   - Low bulk density (<0.9 Mg/m³)
   - High WHC

4. Smectitic soils
   - Loamy to clayey soils of alluvial origin (delta & river plains)
   - Moderate to large amounts of smectites with shrink and swell ability
   - Moderate to high CEC, high base saturation and WHC

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What are the consequences of tropical humid climates for soil properties?

• Physical weathering, erosion and sedimentation
• Intensive vegetation/biomass development
• Fast organic matter turnover
• Increased acidification
• Leaching of salts, carbonates, basic cations
• Strong chemical weathering of primary minerals
• Formation of secondary minerals (clay minerals)
• Weathering of secondary minerals
• Release of Si and Al from clay minerals
• Free Al and Fe and Al and Fe-oxide accumulation
• Phosphorus fixation
• Low nutrient content (also trace elements) 

Why are moore high in acidity: Multiple choice. Low temp. ­ slow OM turnover, parent material poor in cations, strong leaching of cations, addition of rainwater / spring water

How can you raise a soil's CEC ? Explain the mechanism.

How can you influence CEC of clay particle (multiple choice)

Fill out the diagram of different parent materials deposits. (only 4 gaps: Alluvial/fluvial, lacustrine, colluvial (gravity) and eolian (wind)

Name influencing factors in water erosion?

Predicted annual soil loss: A = R x K x LS x C x P
R = rainfall erosivity
K = soil erodibility
L = slope length
S = slope gradient or steepness
C = cover and management
P = erosion-control practices

How can soil erosion by water be reduced?

1. Reduce raindrop impact
-> cover crops/mulches for rainy season
2. Increase infiltration and reduce runoff 
-> modify slope, mulches
3. Reduce runoff velocity
->  modify slope, contour cropping 
4. Safe runoff removal
-> grassed waterways
5. Vegetative barriers
-> perpendicular to slope direction 
-> dense stem system filters particles from runoff
e.g. vetiver grass
6. Minimize soil disturbance 
-> conservation tillage
e.g. chisel plowing stirs soil but only partially incorporates residues -> improves macroporosity, aggregation, infiltration and WHC

What are the influencing factors of soil erosion by wind?

Predicted wind erosion: E = f(I x C x K x L x V)
I = soil erodibility factor
C = climate factor
K = soil-ridge roughness factor
L = width of field factor
V = vegetative cover factor

How can soil erosion by wind be reduced?

1) Stabilize aggregates with OM
2) Plant cover crops to shield and anchor soil
3) Cultivate at right angles to dominant wind direction
4) Standing stubble to absorb shear stress of wind
5) Wind barriers e.g trees and perennial grass  trap wind-blown soil  reduce fetch (distance of unhindered travel) and wind velocity  effects felt at lengths 20 times the height of trees