APBI 200 Exam Questions with Verified Answers Latest Update 2025-2026
The proportion of sand, silt and clay in a soil defines its: - Answers soil texture
A mineral particle that has a mean equivalent diameter between 0.05 - 0.002 mm is called: -
Answers silt-sized particle diameter
A mineral particle that has a mean equivalent diameter between less than 0.002 mm is called -
Answers clay sized particle diameter
A mineral particle that has a mean equivalent diameter between 0.05-2mm is clalled - Answers
sand sized particle diameter
Clay-sized particles have a proportionally greater impact on soil properties than silt and sand-
sized particles because: - Answers clay has a high specific surface area
what is the difference between particle density & bulk density? - Answers particle density is the
weight of solids divided by the volume of solids.
bulk density is the weight (oven dried) of soil divided by the total volume (solids plus pores).
Since the bulk density includes pore space, which is generally about 50%, the bulk density of
soils should be approximately 1/2 of the particle density.
what is the relationship between soil compaction and bulk density - Answers soil compaction
increases bulk density.
what does high bulk density indicate and what does this result in? - Answers poor soil porosity
and soil compaction. it may cause restrictions to root growth and poor water/air movement. soil
also becomes increasingly compacted with depth
Because of their greater surface area per unit of soil mass, clay loams generally have a greater
capacity than loamy sand soils to... - Answers support growth, absorb gasses and nutrients,
release nutrients by mineral weathering
Silicate minerals are... - Answers earths most common mineral (example: quartz)
consists of silica tetrahedra, made up of silicon and oxygen,
what is the fundamental property of silicate minerals? - Answers SiO4 tetrahedron structure
what is soil? - Answers a dynamic natural body composed of mineral and organic solids, gasses,
liquids, and living organisms which can serve as a medium for plant growth
,soil is a ____ and _______ resource - Answers finite and non-renewable
5 factors affecting soil formation - Answers parent material, climate, biota, topography, time
what are parent materials? difference between residual/sedentary, cumulous, transported -
Answers unconsolidated chemically weathered mineral or organic matter.
residual: sediments developed in place from underlying rock over a long period of weathering
cumulose: organic deposits developed in place under a water table
transported: loose sediments that were transported by natural elements
what are some transportation modes of deposition - Answers water, water and ice, ice, wind,
gravity
what does climate determine in terms of soil formation? - Answers the nature (chem, phys, bio)
properties and rate of weathering of soil
how does biota affect soil formation? - Answers soil development is affected by both type and
number of organisms in the soil
how does topography, slope, and time affect soil formation? - Answers interaction with
vegetation affects soil stability/formation. slope affects the relative rate of water infiltration,
vegetation, surface runoff, and soil erosion. soil formation takes place over a very long time
describe a polypedon - Answers *view image
what is a soil profile? what are the 3 layers in the soil horizon and what makes them different
from each other? - Answers soil profile is the 2 dimensional vertical section of the soil from the
surface through all its horizons.
the soil horizon is the layer of soil approximately parallel to the surface, differentiating in phys,
chem, and bio properties (A,B,C = regolith *see image)
difference between mineral and organic soil? what do these two properties make up? - Answers
mineral soil contain less than 30% organic materials, organic soils contain more than 30%
organic material (by weight). together they make up the soil matrix, which contains soil pores
(filled with air/water)
what is humus? - Answers organic material
what are the mineral constituents in soil? (particles with a diameter less than 2) and what do
they're relative proportions indicate - Answers sand, silt, clay (primary particles)
,they're proportions determine soil texture
describe loam soil - Answers textural class with roughly equal proportions of sand, silt, clay
what is the process of weathering? - Answers refers to the breakdown and changes
in rocks and minerals at or near the earth's surface
produced by biological, chemical, and physical
agents or combinations of them
describe physical weathering - Answers disintegration is caused by temperature changes.
different temperatures cause tiny cracks which become larger. water/rain amplifies this
process. this alone is not enough to make soil
exfoliation is caused by the fact that the outer surface of rock is often warmer or colder than
inner more protected portions
describe chemical weathering - Answers hydration (addition of water), hydrolysis (the chemical
breakdown of a compound due to reaction with water), dissolution/solution (release of ions into
soil), carbonation, oxidation-reduction
all of these weaken rocks and make them more susceptible to other processes
describe biological weathering - Answers burrowing animals (cause pulverization), lichens can
cause bio-chem changes that enhance nutrient uptake
5 factors of soil formation - Answers climate: precipitation and temp
biota: vegetation, microbes, soil animals, humans
parent material: unconsolidated material in which soil development occurs
topography: slope, aspect, elevation
time: amount that parent materials are subject to formation
5 soil formation factors are active simultaneously and
interdependently
what is soil physics - Answers is the branch of soil science that deals with the state and
, transport of matter and transformations of energy in the
soil
3 phases of soil - Answers solid: mineral and organic
liquid: water and solutes such as ions, organic compounds, gas
gas: O2, CO2, N2, etc
what is the porosity in mineral soils - Answers In most mineral soils porosity is about
0.3-0.6 (30-60%)
properties of sand? - Answers (0.05 - 2 mm)
small specific surface area
inert (not reactive)
properties of clay? - Answers (<0.002 mm)
large specific surface area
reactive, behave as colloids
what is specific surface area? - Answers Specific surface area = area / mass [m2/g]
what is a soil colloid? - Answers extremely small particles of soil with particle sizes of 2
micrometers in diameter or smaller suspended in a soil with larger particles. Soil colloids are
typically found in clay or humus soils.
Influence of mineral soil particles on soil properties - Answers sand/silt/clay
water holding capacity -low, med-high, high
aeration - good, med, poor
ability to store nutrients- poor, med-high, high
what is a phyllosilicate - Answers are sheet silicate minerals, formed by parallel sheets of
silicate tetrahedra with Si2O5 or a 2:5 ratio
describe isomorphic substitution - Answers process by which one element fills a position
usually filled by another of similar size and valence.
It leads to formation of permanent charge on clay minerals.
The proportion of sand, silt and clay in a soil defines its: - Answers soil texture
A mineral particle that has a mean equivalent diameter between 0.05 - 0.002 mm is called: -
Answers silt-sized particle diameter
A mineral particle that has a mean equivalent diameter between less than 0.002 mm is called -
Answers clay sized particle diameter
A mineral particle that has a mean equivalent diameter between 0.05-2mm is clalled - Answers
sand sized particle diameter
Clay-sized particles have a proportionally greater impact on soil properties than silt and sand-
sized particles because: - Answers clay has a high specific surface area
what is the difference between particle density & bulk density? - Answers particle density is the
weight of solids divided by the volume of solids.
bulk density is the weight (oven dried) of soil divided by the total volume (solids plus pores).
Since the bulk density includes pore space, which is generally about 50%, the bulk density of
soils should be approximately 1/2 of the particle density.
what is the relationship between soil compaction and bulk density - Answers soil compaction
increases bulk density.
what does high bulk density indicate and what does this result in? - Answers poor soil porosity
and soil compaction. it may cause restrictions to root growth and poor water/air movement. soil
also becomes increasingly compacted with depth
Because of their greater surface area per unit of soil mass, clay loams generally have a greater
capacity than loamy sand soils to... - Answers support growth, absorb gasses and nutrients,
release nutrients by mineral weathering
Silicate minerals are... - Answers earths most common mineral (example: quartz)
consists of silica tetrahedra, made up of silicon and oxygen,
what is the fundamental property of silicate minerals? - Answers SiO4 tetrahedron structure
what is soil? - Answers a dynamic natural body composed of mineral and organic solids, gasses,
liquids, and living organisms which can serve as a medium for plant growth
,soil is a ____ and _______ resource - Answers finite and non-renewable
5 factors affecting soil formation - Answers parent material, climate, biota, topography, time
what are parent materials? difference between residual/sedentary, cumulous, transported -
Answers unconsolidated chemically weathered mineral or organic matter.
residual: sediments developed in place from underlying rock over a long period of weathering
cumulose: organic deposits developed in place under a water table
transported: loose sediments that were transported by natural elements
what are some transportation modes of deposition - Answers water, water and ice, ice, wind,
gravity
what does climate determine in terms of soil formation? - Answers the nature (chem, phys, bio)
properties and rate of weathering of soil
how does biota affect soil formation? - Answers soil development is affected by both type and
number of organisms in the soil
how does topography, slope, and time affect soil formation? - Answers interaction with
vegetation affects soil stability/formation. slope affects the relative rate of water infiltration,
vegetation, surface runoff, and soil erosion. soil formation takes place over a very long time
describe a polypedon - Answers *view image
what is a soil profile? what are the 3 layers in the soil horizon and what makes them different
from each other? - Answers soil profile is the 2 dimensional vertical section of the soil from the
surface through all its horizons.
the soil horizon is the layer of soil approximately parallel to the surface, differentiating in phys,
chem, and bio properties (A,B,C = regolith *see image)
difference between mineral and organic soil? what do these two properties make up? - Answers
mineral soil contain less than 30% organic materials, organic soils contain more than 30%
organic material (by weight). together they make up the soil matrix, which contains soil pores
(filled with air/water)
what is humus? - Answers organic material
what are the mineral constituents in soil? (particles with a diameter less than 2) and what do
they're relative proportions indicate - Answers sand, silt, clay (primary particles)
,they're proportions determine soil texture
describe loam soil - Answers textural class with roughly equal proportions of sand, silt, clay
what is the process of weathering? - Answers refers to the breakdown and changes
in rocks and minerals at or near the earth's surface
produced by biological, chemical, and physical
agents or combinations of them
describe physical weathering - Answers disintegration is caused by temperature changes.
different temperatures cause tiny cracks which become larger. water/rain amplifies this
process. this alone is not enough to make soil
exfoliation is caused by the fact that the outer surface of rock is often warmer or colder than
inner more protected portions
describe chemical weathering - Answers hydration (addition of water), hydrolysis (the chemical
breakdown of a compound due to reaction with water), dissolution/solution (release of ions into
soil), carbonation, oxidation-reduction
all of these weaken rocks and make them more susceptible to other processes
describe biological weathering - Answers burrowing animals (cause pulverization), lichens can
cause bio-chem changes that enhance nutrient uptake
5 factors of soil formation - Answers climate: precipitation and temp
biota: vegetation, microbes, soil animals, humans
parent material: unconsolidated material in which soil development occurs
topography: slope, aspect, elevation
time: amount that parent materials are subject to formation
5 soil formation factors are active simultaneously and
interdependently
what is soil physics - Answers is the branch of soil science that deals with the state and
, transport of matter and transformations of energy in the
soil
3 phases of soil - Answers solid: mineral and organic
liquid: water and solutes such as ions, organic compounds, gas
gas: O2, CO2, N2, etc
what is the porosity in mineral soils - Answers In most mineral soils porosity is about
0.3-0.6 (30-60%)
properties of sand? - Answers (0.05 - 2 mm)
small specific surface area
inert (not reactive)
properties of clay? - Answers (<0.002 mm)
large specific surface area
reactive, behave as colloids
what is specific surface area? - Answers Specific surface area = area / mass [m2/g]
what is a soil colloid? - Answers extremely small particles of soil with particle sizes of 2
micrometers in diameter or smaller suspended in a soil with larger particles. Soil colloids are
typically found in clay or humus soils.
Influence of mineral soil particles on soil properties - Answers sand/silt/clay
water holding capacity -low, med-high, high
aeration - good, med, poor
ability to store nutrients- poor, med-high, high
what is a phyllosilicate - Answers are sheet silicate minerals, formed by parallel sheets of
silicate tetrahedra with Si2O5 or a 2:5 ratio
describe isomorphic substitution - Answers process by which one element fills a position
usually filled by another of similar size and valence.
It leads to formation of permanent charge on clay minerals.
