SSC Exam 2

Which of the following complete reactions describes why natural rainfall is slightly acidic?

H2O + SO2 + ½O2 2H+ + SO4-2

CO3-2 + 2H+ CO2 + H2O

H2O + CO2 CO3-2 + 2H+

H2O + CO2 CO + H2O2

H2O + CO2 CO3-2 + 2H+

Soil forming factors:

parent material,

time,

climate,

organisms (biology),

topography

In the following list of soil parameters or processes, indicate how enhancing soil biological activity influences each

A. Soil formation

B. Soil Aggregation

C. Soil Structure

D. Crop Productivity

E. Soil Areation

F. Soil Texture

G. Infiltration

A. Enhances

B. Enhances

C. Enhances

D. Increases

E. Increases

F. No effect

G. Increases

fungi can be used by humans as a food source

True

a toeslope represents the top of a variable sloped landscape

False

soils developed under grasses exhibit higher soil OM content than under forests

True

acid soils often contain Na+ that can reduce productivity in some crops

False

the most weathered soils occur in climates with highest rainfall and temperatures

True

slope aspect represents the steepness of a slope

False (it represents the direction the slope faces)

soil development & soil depth generally increases with increasing infiltration & percolation

True

Some microorganisms require plants to exist in soil. Describe two symbiotic relationships

N2 fixing bacteria(Rhizobium) - bacteria infect a root hair, the root supplies C to bacteria....Bacteria convert N2 to NH4 for plant use, as the legume roots decompose soil N increases

Mychorrizal fungi - fungi gets C from the plants and they also increase nutrient and H2O uptake

Rainfall pH that is lower than natural rainfall is commonly caused by which of the following reactions?

NH4+ + 2O2 NO3- + 2H+ + H2O

CO3-2 + 2H+ CO2 + H2O

H2O + CO2 CO + H2O2

SO2 + H2O + ½O2 2H+ + SO4-2

SO2 + H2O + ½O2 2H+ + SO4-2

Define nitrogen mineralization and how it benefits N availability to plants

Process where bacteria and fungi take organic nutrients and convert it to inorganic nutrients which increases N availability to plants and it is a very important nitrogen conservation process

Most soils are developed from parent materials transported from one place to another by (select one):

volcanoes, floods, wind, earthquakes

ice, water, gravity, wind

water, wind, animals, earthquakes

gravity, wind, animals, rivers

ice, water, gravity, wind

weathering of parent materials initiates soil formation

True

earthworms and other burrowing organisms improve infiltration, percolation, and rooting depth

True

mycorrhizae are bacteria that increase soil volume explored by roots

False

more lime is required to raise soil pH from 4.5 to 6 in a clay soil than in a sandy soil

True

sandy soils eventually weather to clay soils

False

slope grade represents the direction the slope faces

False (it represents the steepness of the slope)

calcareous and alkaline soils are common in humid regions

False

fungi are microorganisms isolated from soils used to produce antibiotics

False

there are many plants that can tolerate or prefer acid soils

True

a liming material should neutralize acids and bases in soil

False

in saturated soils, anaerobic bacteria convert nitrate (NO3-) to nitrogen gas (N2)

True

sodic soils commonly occur in regions of high weathering intensity

False

the source of parent material determines soil texture

True

a calcareous soil contains CaCO3 and has a soil pH <7

False

Soil development is enhanced on a north-facing slope compared to a south-facing slope because of....

- greater infiltration and reduced runoff results in lower evaporation and higher precipitation

- lower evaporation results in higher percolation, plant available water, and plant growth

- lower evaporation results in lower infiltration, plant available water, and plant growth

- lower infiltration and runoff results in greater plant growth and soil development

lower evaporation results in higher percolation, plant available water, and plant growth

Soil depth on a toeslope is greater than on a sideslope because.....

- lower soil erosion on a sideslope increases soil transport to the toeslope

- greater soil erosion on the toeslope increases soil development on the sideslope

- runoff from the sideslope increases infiltration, percolation, and plant growth on the toeslope

- lower infiltration and percolation increases soil depth on the toeslope

runoff from the sideslope increases infiltration, percolation, and plant growth on the toeslope

Describe the 4 horizons (O, A, B, C)

TOPSOIL

O Horizon - mostly Organic Matter,

A Horizon - clays + Organic Matter, High Organic Matter, H2O holding, nutrient content

SUBSOIL

B Horizon - suspended (fine clay), high H20 holding, low Organic matter and nutrient content

C Horizon - clays, partially altered parent rock

E Horizon is between A & B

breaking of rocks into smaller pieces < particle size > surface area

physical weathering

à an historical record of environmental (weathering) processes at a particular point in the landscape

soil profile

4 types of physical weathering

frost wedging

heating & cooling

Wetting & drying

Grinding

freezing/thawing (H2O) in cracks disintegrates rocks H2O expands when frozen ... pushes cracks apart .... freeze-thaw cycles deceases rock size...increasing surface area, which increases chemical weathering

Frost Wedging

particles expand/contract with increasing /decreasing temperature

Heating & cooling

some minerals shrink and swell with wet-dry cycle

Wetting & drying

grinding of particles against each other accelerates particle disintegration

Grinding

Ph of unpolluted rainfall is

5.7

Identify the relationship between physical and chemical weathering

Physical weathering is when the rock is broken down by wind, gravity, ice, or water

Chemical weathering is when a rock is broken down by a reaction between a rock and another substance i.e. acid rain

Processes that transport soils

Windblown (loess)

Water deposited

-Glacial till

Alluvial Materials (Histisols)

Antibiotics are produced by

actinomycetes (streptomyces)

Difference between mineralization and immobilization

Mineralization - Organic N --> Inorganic N

- provides plant available N

Immobilization - Organic N <-- Inorganic N

- conserves/stores N for later mineralization

- reduces plant available N

Other Bacteria

Nitrifying, denitrifying