AP®︎ Environmental Science: Topic 4.3 Flashcards

A mixture of mineral particles, organic matter, water, air, and organisms; idealized productive surface soil is 45% mineral matter, 25% water, 25% air, and 5% organic matter by volume

The living organisms, roots, recently dead material, and humus in soil that influence water retention, nutrient supply, and structure

Dark, relatively stable organic material formed by decomposition that helps soil retain water and nutrients and improves structure

The relative percentages of sand, silt, and clay in the mineral portion of soil

The way individual soil particles are grouped into aggregates, distinct from the particle percentages measured by texture

The largest mineral soil particles, 0.05–2.0 mm in diameter; sandy soils are generally highly permeable and retain little water or nutrients

Intermediate-sized mineral soil particles, 0.002–0.05 mm in diameter, that often feel smooth or flour-like when dry

The smallest mineral soil particles, less than 0.002 mm in diameter; clay-rich soils generally transmit water slowly and retain substantial water and nutrient cations

Macropores are large pores that transmit water rapidly; micropores are small pores that transmit water slowly and hold it more strongly

The percentage of total soil volume occupied by pore space: pore-space volume ÷ total soil volume × 100

Compression of soil that destroys pore space, reducing porosity, permeability, infiltration, aeration, and root growth while increasing runoff

Dry soil mass per total soil volume; a higher bulk density generally indicates greater compaction and less pore space

The ability of soil to transmit water through connected pore spaces

The process by which water enters soil at its surface, influenced by texture, vegetation, crusting, slope, and compaction

Place equal soil depths in identical columns with the same packing, add equal water volumes, and compare drainage time or discharge per unit time; faster drainage indicates greater permeability

The total amount of water a soil can retain in its pores and on particle surfaces

The amount of water remaining in soil after excess gravitational water has drained away

The soil-water level at which plants can no longer extract enough water and remain wilted

The water plants can extract from soil, equal to field capacity minus the permanent wilting point

Dry equal soil masses, saturate and drain them identically, then calculate retained water as drained wet mass minus dry mass

The ability of soil to supply nutrients and other conditions needed for plant growth

The reversible transfer of positively charged nutrient ions between negatively charged soil particles and soil water

A soil’s ability to hold and exchange nutrient cations; soils rich in clay and humus generally have higher CEC than sandy soils

A logarithmic measure of soil acidity or basicity that affects nutrient availability, microbial activity, and plant growth

Mix soil with distilled or deionized water at a consistent ratio, allow it to settle, and test the liquid with a calibrated probe or indicator

The concentration of dissolved salts in soil; high salinity interferes with plant water uptake and is often estimated by electrical conductivity

The conversion by soil organisms of nutrients in organic matter into inorganic forms that plants can absorb

Incubate equal masses of moist soil under controlled conditions and measure CO₂ released; greater release generally indicates greater biological activity

A diagram that classifies mineral soil from sand, silt, and clay percentages summing to 100%; plot the three percentage lines and identify their textural region

A textural class containing a balanced mixture of sand, silt, and clay that commonly provides both water retention and drainage; it is not necessarily equal thirds

Mix soil with water and let it settle into sand, silt, and clay layers; each percentage is layer thickness ÷ total mineral-layer thickness × 100

Weigh dry soil, heat it until organic matter burns away, and use the lost mass to estimate percent organic matter

Physical tests measure traits such as texture and permeability; chemical tests measure pH, nutrients, salinity, or CEC; biological tests measure organisms and their activity

A representative sample made by collecting soil at a consistent depth from several locations and combining it, while sampling visibly different areas separately