Chapter 31: Soil and Plant Nutrition Flashcards
What are the essential nutrients for plants, and how are they categorized?
17 essential nutrients:
Macronutrients: Required in large amounts (e.g., C, H, O, N, P, K, Ca, Mg, S).
Micronutrients: Needed in trace amounts (e.g., Fe, Mn, Zn, Cu, B, Mo, Cl, Ni).
Criteria: Required for life cycle completion; irreplaceable by another element.
What roles do nitrogen (N), phosphorus (P), and potassium (K) play in plants?
N: Component of amino acids, chlorophyll, nucleic acids.
P: ATP, phospholipids, nucleic acids.
K: Enzyme activation, stomatal regulation, osmotic balance.
Describe chlorosis and necrosis in nutrient-deficient plants.
Chlorosis: Yellowing due to lack of chlorophyll (e.g., nitrogen/magnesium deficiency).
Necrosis: Tissue death (e.g., calcium deficiency causes terminal bud die-off).
What are the soil horizons, and what defines each layer?
O horizon: Organic matter (leaf litter, decomposing organisms).
A horizon (topsoil): Mineral particles + organic matter (humus).
B horizon (subsoil): Accumulated clays/nutrients leached from above.
C horizon: Weathered parent rock.
What is soil texture, and how does it affect plant growth?
Texture: Proportions of sand, silt, and clay.
Loam (40% sand, 40% silt, 20% clay): Ideal for water retention, drainage, and aeration.
Clay soils: Poor drainage but high nutrient retention.
How does soil pH influence nutrient availability?
Acidic soils (pH < 6): Increase Al³+ toxicity; reduce P, Ca, Mg availability.
Alkaline soils (pH > 7): Limit Fe, Mn, Zn uptake.
Most crops thrive at pH 6–7.
What is cation exchange capacity (CEC)?
Soil’s ability to hold positively charged ions (e.g., NH₄⁺, K⁺, Ca²⁺).
High CEC (clay/humus-rich soils) = better nutrient retention.
Describe mycorrhizae and their symbiotic role.
Mutualism: Fungi colonize plant roots.
Fungi: Provide water/minerals (e.g., P).
Plant: Supplies sugars to fungi.
How do Rhizobium bacteria benefit legumes?
Nitrogen fixation: Convert atmospheric N₂ to NH₃ (ammonia) in root nodules.
Leghemoglobin: Protects nitrogenase enzyme from O₂.
What are carnivorous plants, and why do they trap prey?
Grow in nutrient-poor soils (e.g., bogs).
Examples: Venus flytrap, pitcher plants.
Digest insects to supplement nitrogen/phosphorus.
What is epiphytic vs. parasitic plant nutrition?
Epiphytes (e.g., orchids): Grow on other plants for support (no nutrient theft).
Parasites (e.g., mistletoe): Steal water/nutrients from host via haustoria.
How do halophytes adapt to saline soils?
Salt glands: Excrete excess salt (e.g., mangroves).
Osmotic adjustments: Accumulate solutes to retain water.
What is the nitrogen cycle, and how do plants participate?
Fixation (N₂ → NH₃ by bacteria).
Nitrification (NH₃ → NO₃⁻ by soil bacteria).
Assimilation (plants absorb NO₃⁻/NH₄⁺).
Denitrification (NO₃⁻ → N₂ by anaerobic bacteria).
What is crop rotation, and why is it used?
Alternating crops (e.g., legumes with grains) to replenish soil nitrogen and reduce pest buildup.
How do fertilizers differ from organic amendments (e.g., compost)?
Fertilizers: Synthetic, concentrated nutrients (NPK ratios).
Organic amendments: Improve soil structure, water retention, and microbial activity.
