Answer: A. Minerals, organic matter, water, air. Soil contains mineral and organic solids, water and air. Their proportions vary by soil and conditions.
Which acronym summarizes five soil-forming factors?
A CEC
B SAR
C USDA
D CLORPT
Answer: D. CLORPT. CLORPT stands for climate, organisms, relief, parent material and time, which interact during soil formation.
In soil genesis, what is parent material?
A The top layer of leaves
B The deepest groundwater layer
C A field’s crop residue
D Material soil forms from
Answer: D. Material soil forms from. Parent material is the mineral or organic material in which soil development begins.
How do soil organisms help nutrient cycling?
A Remove every soil pathogen
B Decompose residues and recycle nutrients
C Convert sand into clay
D Stop all mineral weathering
Answer: B. Decompose residues and recycle nutrients. Microorganisms and other soil life decompose residues and transform nutrients into forms that move through soil systems.
What does a soil profile describe?
A Vertical sequence of soil horizons
B A list of fertilizer products
C A field’s rainfall record
D A map of crop yields
Answer: A. Vertical sequence of soil horizons. A soil profile is the vertical arrangement of horizons observed through the soil.
Where is the O horizon generally found?
A Inside the water table
B Only beneath subsoil
C At the organic surface
D Below unweathered bedrock
Answer: C. At the organic surface. The O horizon consists mainly of surface organic material, such as litter and decomposing residues.
Which description best fits an A horizon?
A Mineral topsoil with organics
B Fresh unweathered bedrock
C Only loose surface litter
D Deep groundwater deposit
Answer: A. Mineral topsoil with organics. The A horizon is commonly the mineral surface horizon, often mixed with organic matter.
In many profiles, what does an E horizon indicate?
A A permanent water table
B A zone of leaching
C A zone of salt buildup
D The parent rock surface
Answer: B. A zone of leaching. An E horizon is an eluvial layer from which materials have been removed or leached.
What often accumulates in a developed B horizon?
A Surface water only
B Clay and iron compounds
C Unweathered plant litter
D Fresh crop residues
Answer: B. Clay and iron compounds. Many B horizons show accumulation or transformation of materials moved from upper horizons, though profiles differ.
Which material is commonly associated with the C horizon?
A Fresh leaf litter
B A surface crust only
C Weakly altered parent material
D A cultivated seedbed
Answer: C. Weakly altered parent material. The C horizon is relatively little affected by soil-forming processes compared with upper horizons.
How does weathering contribute to soil formation?
A Eliminates biological activity
B Breaks down parent material
C Stops horizon development
D Creates rainfall from minerals
Answer: B. Breaks down parent material. Physical and chemical weathering break down or transform parent material over time.
Which proportions define mineral soil texture?
A Carbon, nitrogen, and sulfur
B Humus, salts, and gravel
C Water, air, and roots
D Sand, silt, and clay
Answer: D. Sand, silt, and clay. Texture is determined by the relative proportions of sand, silt and clay in the fine-earth fraction.
From coarsest to finest, how are soil particles ordered?
A Clay, sand, silt
B Sand, silt, clay
C Sand, clay, silt
D Silt, clay, sand
Answer: B. Sand, silt, clay. In the USDA system, sand particles are coarser than silt, which is coarser than clay.
When moistened, how does clay commonly feel?
A Floury; never forms ribbons
B Smooth; drains instantly
C Gritty; will not cohere
D Sticky; forms a long ribbon
Answer: D. Sticky; forms a long ribbon. Clayey soil commonly feels sticky and can form a ribbon when worked at suitable moisture.
How does silt often feel when moist?
A Sharp and gravelly
B Very gritty and loose
C Highly sticky and plastic
D Smooth or floury
Answer: D. Smooth or floury. Silt often feels smooth or floury, unlike the gritty feel of sand and sticky feel of clay.
What is soil structure?
A Arrangement into soil aggregates
B Amount of water after drainage
C Relative sand and clay amounts
D Soil reaction measured by pH
Answer: A. Arrangement into soil aggregates. Soil structure describes how particles bind into aggregates, also called peds.
What do soil scientists call a natural aggregate?
A A pore
B A profile
C A ped
D A horizon
Answer: C. A ped. A ped is an individual natural unit of soil structure.
Which definition best describes soil porosity?
A Volume share occupied by pores
B Depth of the soil profile
C Dry mass per soil area
D Proportion of sand particles
Answer: A. Volume share occupied by pores. Porosity is the share of soil volume occupied by pore spaces, which may contain air or water.
How is bulk density calculated?
A Wet mass per pore volume
B Clay mass per soil area
C Water volume per root length
D Dry mass per total volume
Answer: D. Dry mass per total volume. Bulk density is dry soil mass divided by its total volume, including pore spaces.
What can compaction do to root growth?
A Remove all surface runoff
B Increase every pore size
C Restrict roots and water movement
D Improve aeration in all soils
Answer: C. Restrict roots and water movement. Compaction can reduce pore space and restrict roots, infiltration or air movement, depending on severity and soil.
After free gravitational water drains, what remains at field capacity?
A Only water bound in minerals
B All water in saturated pores
C Water held after drainage
D Water below wilting point
Answer: C. Water held after drainage. Field capacity describes water remaining after excess gravitational water has drained from a wetted soil.
At the permanent wilting point, what happens to plants?
A They reach maximum water uptake
B They release excess soil salts
C They cannot recover
D They begin seed germination
Answer: C. They cannot recover. At permanent wilting point, most plants cannot recover from wilting even when moisture is supplied.
How is available water capacity commonly defined?
A Field capacity minus wilting point
B Sand fraction minus clay fraction
C Porosity minus bulk density
D Rainfall minus runoff
Answer: A. Field capacity minus wilting point. Available water capacity is the water held between field capacity and permanent wilting point.
Compared with loam, what often characterizes sandy soil?
A Faster drainage, less water storage
B Higher cohesion, less aeration
C Slower drainage, more clay
D More storage in every soil
Answer: A. Faster drainage, less water storage. Coarse sandy soils often drain rapidly and hold less available water than loamy soils, though depth and structure also matter.
Why can clay retain water tightly?
A Its particles are always dry
B Its small pores hold water
C It contains no air spaces
D Its grains are largest
Answer: B. Its small pores hold water. Fine pores in clay can retain water strongly; some retained water may be unavailable to plants.
In soil hydrology, what is infiltration?
A Salt movement into plants
B Water entry through soil surface
C Downward flow in bedrock
D Water loss from leaves
Answer: B. Water entry through soil surface. Infiltration is the entry of water into soil at the surface.
Once water has entered soil, what is percolation?
A Runoff across a field
B Evaporation from leaf surfaces
C Downward movement through layers
D Nutrient uptake by roots
Answer: C. Downward movement through layers. Percolation refers to water moving downward through soil layers under gravity and pressure gradients.
During intense rainfall, what can runoff carry from bare slopes?
A Groundwater into the atmosphere
B Clay upward into leaves
C Detached soil downslope
D Organic matter into bedrock
Answer: C. Detached soil downslope. Runoff can detach and transport topsoil, especially where slopes are bare or poorly protected.
How does a residue cover reduce splash erosion?
A Removes all surface pores
B Makes rainwater more acidic
C Increases slope length
D Shields soil from raindrop splash
Answer: D. Shields soil from raindrop splash. Residue cover cushions raindrop impact and can reduce soil detachment and runoff.
What is humus in soil?
A Salt crystals from irrigation
B Relatively stable decomposed organic matter
C Water held in large pores
D Fresh unbroken mineral rock
Answer: B. Relatively stable decomposed organic matter. Humus is relatively stable organic material formed through decomposition and transformation of residues.
During mineralization, what happens to nutrients?
A Plants convert clay into sand
B Microbes release inorganic forms
C Salts become organic matter
D Roots remove every nutrient
Answer: B. Microbes release inorganic forms. Microbial mineralization converts some organic nutrients into inorganic forms that may become available to plants.
What does cation exchange capacity indicate?
A Ability to retain positive ions
B Rate of soil surface runoff
C Capacity to hold only water
D Sample sand proportion
Answer: A. Ability to retain positive ions. CEC describes the soil’s capacity to retain exchangeable cations, including several plant nutrients.
Why does cation exchange capacity not hold nitrate like a cation?
A Nitrate is a negative ion
B Nitrate is always organic
C Nitrate is a soil horizon
D Nitrate contains no nitrogen
Answer: A. Nitrate is a negative ion. Nitrate is an anion; negatively charged exchange surfaces generally do not retain it the way they retain cations.
How would you classify soil with pH 5.5?
A Neutral
B Saline
C Alkaline
D Acidic
Answer: D. Acidic. A pH below 7 is acidic on the standard pH scale.
Why can soil pH affect crop nutrition?
A It changes nutrient availability
B It determines rainfall amounts
C It fixes soil texture
D It measures root depth
Answer: A. It changes nutrient availability. Soil pH affects chemical reactions and the availability of many nutrients to plants.
What does electrical conductivity help indicate in soil?
A Soil temperature at harvest
B Total sand percentage
C Concentration of soluble salts
D Depth of the A horizon
Answer: C. Concentration of soluble salts. Electrical conductivity is commonly used to assess soluble-salt concentration; interpretation depends on the measurement method.
Which condition is sodicity associated with?
A Low sand content alone
B Excess exchangeable sodium
C Excess plant-available oxygen
D High organic matter only
Answer: B. Excess exchangeable sodium. Sodicity concerns excessive exchangeable sodium, which can damage soil structure and water movement.
Why can salinity stress crop plants?
A It removes all clay particles
B It always increases soil oxygen
C It converts nitrate to gas
D It makes water uptake harder
Answer: D. It makes water uptake harder. High soluble salts can make it harder for plants to take up water and may impair growth.
What should be done when a white crust suggests salinity?
A Assume the whole field matches
B Remove topsoil immediately
C Test soil and water samples
D Apply fertilizer without sampling
Answer: C. Test soil and water samples. Visual signs can suggest salt problems, but laboratory measurements help identify the type and severity.
Before nutrient analysis, how should a field sample be collected?
A Choose only visibly dark spots
B Mix soil from unlike zones
C Sample only the field edge
D Use representative sampling locations
Answer: D. Use representative sampling locations. Representative sampling across a management area helps a laboratory result reflect the field being assessed.
Why can nitrate leach readily in many soils?
A It forms a stable mineral
B It is a mobile anion
C Held by charged surfaces
D It cannot dissolve in water
Answer: B. It is a mobile anion. Nitrate is negatively charged and can move with percolating water; leaching risk depends on soil, water and management.
When adjusting soil pH, what should guide the decision?
A Lab results and recommendations
B Soil color by itself
C One dose for all fields
D Last year’s crop price
Answer: A. Lab results and recommendations. Amendment choices and rates should follow soil-test results, crop needs and locally appropriate recommendations.
What can retained soil organic matter support?
A Identical pH across horizons
B Aggregation and nutrient retention
C Complete control of weeds
D Permanent immunity to erosion
Answer: B. Aggregation and nutrient retention. Organic matter can support aggregation, nutrient retention and other soil functions, with effects varying by context.
What do decomposers contribute to soil systems?
A Prevent every disease
B Create all mineral particles
C Break down organic residues
D Stop nutrient transformations
Answer: C. Break down organic residues. Bacteria, fungi and other decomposers break down residues and participate in nutrient cycling.
How can earthworms influence soil?
A Mix soil and process residues
B Prevent all crop pests
C Remove every compacted layer
D Set the soil’s pH
Answer: A. Mix soil and process residues. Earthworms can mix soil and process organic residues, though their abundance and effects vary by environment.
Under waterlogged conditions, what may roots experience?
A Reduced oxygen availability
B Lower soil saturation
C Faster gas exchange
D Permanent nutrient balance
Answer: A. Reduced oxygen availability. Water-filled pores slow oxygen movement, potentially creating oxygen stress for roots.
Which resource helps compare mapped soil properties across a landscape?
A A crop calendar
B A market invoice
C A seed label
D A soil survey
Answer: D. A soil survey. Soil surveys describe mapped soil types and properties, helping compare land characteristics; field checks may still be needed.
Which statement about soil horizons is most accurate?
A Only cultivated soils have horizons
B Every profile has identical layers
C Their sequence varies among soils
D All horizons form at once
Answer: C. Their sequence varies among soils. Horizon number, thickness and development vary with soil-forming factors, age and disturbance.
What supports a robust soil-health assessment?
A Crop yield alone
B Physical, chemical, biological indicators
C One fertilizer test
D Soil color alone
Answer: B. Physical, chemical, biological indicators. NRCS recommends using multiple indicators; soil health cannot be judged from crop yield or another single outcome alone.
On bare sloping land, how can erosion harm productivity?
A It creates deeper topsoil quickly
B It stops runoff completely
C It increases all soil nutrients
D It removes nutrient-rich surface soil
Answer: D. It removes nutrient-rich surface soil. Erosion can remove fertile surface material, reduce soil depth and carry sediment into waterways.