Botany 2: Soil properties and nutrition

Soil

One of the most important natural resources on Earth; composed of air, water, minerals, and organic matter.

Four Main Components of Soil

Air, Water, Minerals, Organic matter.

Soil Texture

The relative amounts of sand, silt, and clay particles in soil; affects water holding capacity, aeration, drainage rate, compaction potential, and nutrient retention.

Soil Texture Triangle

Used to determine soil textural class from percentages of sand, silt, and clay.

Water Holding Capacity

How much water soil can hold so that it is available for plant uptake.

Aeration

Process by which air circulates through soil to provide oxygen for root respiration.

Drainage Rate

Rate at which water passes through soil.

Compaction Potential

How easily soil compacts or compresses.

Erosion Potential

How easily topsoil is lost through erosion or tillage after rainfall.

Nutrient Retention

Ability of soil to store plant nutrients and resist pH changes.

Four Broad Soil Texture Groups

Sandy, Clayey, Silty, and Loamy soils.

Soil Structure

Aggregation of soil particles into peds.

Peds

Aggregates formed by the binding of sand, silt, and clay particles.

Infiltration

Movement of water through soil.

Bulk Density

Mass of dry soil per unit volume, including solid and pore spaces.

Categories of Water in Soil

Gravitational water and Capillary water.

Gravitational Water

Free water that moves through soil by gravity; generally unavailable to plants; occupies macropores.

Capillary Water

Held in soil against gravity; available to plants; found in micropores; moves via adhesion and cohesion.

Field Capacity

Maximum water soil can hold against gravity; water available for crop use.

Rhizobia

Bacteria that convert nitrogen into a usable form for plants.

Mycorrhiza

Fungus that grows with roots, providing nutrients like nitrogen or phosphorus in exchange for carbohydrates; extends root system.

Ions

Atoms or molecules that have lost or gained electrons; include cations (+) and anions (−).

Cation Exchange Capacity (CEC)

Soil’s ability to store and exchange positively charged nutrients (cations).

Five Factors of Soil Formation

Climate, Organisms, Relief, Parent Material, Time.

Weathering

Physical, chemical, and biological processes that create soil.

Humus

Stable organic component that improves soil structure and water holding capacity.

Nutrient Cycling

Soil organisms convert essential nutrients (N, P, K) into plant

Nitrogen Fixation

Rhizobium bacteria convert atmospheric nitrogen into usable forms via symbiosis with legume roots.

Soil Horizon

Layer of soil distinguished by properties and characteristics from formation factors.

Soil Profile

Arrangement of soil layers (horizons) from surface to unconsolidated material.

Essential Elements for Plant Growth

17 total; carbon, hydrogen, and oxygen used to make sugars via photosynthesis.

Macronutrients

Elements required in large amounts for plant growth.

Nitrogen Deficiency

Severe stunting, chlorosis (yellowing) on older leaves.

Nitrogen Role

Protein synthesis, enzyme catalysis, sugar and starch formation, stomatal regulation, cell membrane permeability, turgidity maintenance.

Phosphorus Role

Crucial for photosynthesis and respiration (ATP), DNA component, root growth, seed development, and stem strength.

Calcium Role

Strengthens cell walls; regulates membrane permeability, cytoplasm viscosity, and cell communication.

Magnesium Deficiency

Chlorosis between veins, mottled leaves, stunted growth, leaf tips turned upward, striped appearance.

Sulfur Deficiency

Appears first in young leaves; light green veins; readily leached by heavy rainfall or irrigation.

Boron Role

Crucial for cell wall formation; DNA/RNA synthesis; immobile nutrient—deficiency appears on new growth.

Chlorine Role

Supports root development, photosynthesis, and stomata regulation; highly mobile and prone to leaching.

Copper Deficiency

Twisted or misshapen young leaves; pale or yellow leaves; necrotic spots; stunted growth; twig dieback.

Iron Deficiency

Interveinal chlorosis on young leaves; short slender stems.

Manganese Role

Immobile nutrient activating enzymes, aiding photosynthesis, maintaining chloroplast membranes.

Molybdenum Role

Involved in phosphorus metabolism; deficiency when soil pH is too low; common in poinsettias.

Nickel Role

Needed for conversion of urea to ammonia in legumes; unavailable at high pH; deficiency causes necrosis, curled leaves, stunted growth.

Zinc Role

Component of enzymes; affects auxin production; important for fruit, seed, and root development, photosynthesis, and stress protection.