Soil Biology & Nutrients

Flashcards – Soil Biology & Nutrients

🔹 Soil Organisms & Food Web

Q1: What are the three main categories of soil organisms?
A1: Macrofauna (e.g., earthworms), mesofauna/microfauna (e.g., nematodes), and microorganisms (e.g., bacteria, fungi).

Q2: What is the rhizosphere?
A2: The narrow region of soil directly influenced by root secretions and associated microbial activity.

Q3: What are mycorrhizae?
A3: Symbiotic fungi that associate with plant roots, enhancing nutrient (especially P) and water uptake.

Q4: How do earthworms benefit soil?
A4: They improve structure, aeration, and organic matter mixing, and enhance microbial activity through their casts.

Q5: What is biological nitrogen fixation?
A5: The conversion of atmospheric N₂ into ammonium (NH₄⁺) by bacteria, making nitrogen available to plants.

Q6: Name a symbiotic nitrogen-fixing organism.
A6: Rhizobium bacteria (forms nodules on legume roots).

Q7: What do soil fungi do?
A7: Decompose complex organic materials, form mycorrhizal associations, and help aggregate soil particles.

🔹 Soil Microbial Processes

Q8: What is mineralization?
A8: The microbial conversion of organic nutrients into inorganic forms that plants can absorb.

Q9: What is immobilization?
A9: The conversion of inorganic nutrients into microbial biomass, temporarily making them unavailable to plants.

Q10: When does immobilization dominate over mineralization?
A10: When organic material has a high carbon-to-nitrogen (C/N) ratio (>30:1).

🔹 Nutrient Uptake Mechanisms

Q11: What are the three main nutrient uptake processes?
A11: Mass flow, diffusion, and root interception.

Q12: Describe mass flow.
A12: Nutrients dissolved in water move to roots as water is taken up by the plant.

Q13: Describe diffusion (in the context of soil).
A13: Nutrients move from areas of high concentration to low concentration near the root surface.

Q14: What is root interception?
A14: Roots grow into contact with nutrients present on or near soil particles.

🔹 Major Nutrient Cycles

Q15: What are the key forms of nitrogen plants absorb?
A15: Ammonium (NH₄⁺) and nitrate (NO₃⁻).

Q16: What is nitrification?
A16: The conversion of NH₄⁺ → NO₂⁻ → NO₃⁻ by nitrifying bacteria.

Q17: What is denitrification?
A17: The reduction of NO₃⁻ to N₂ gas by bacteria under anaerobic conditions, resulting in nitrogen loss to the atmosphere.

Q18: Why is nitrate (NO₃⁻) easily lost from soil?
A18: Because it is negatively charged and not held by soil particles; it leaches easily with water.

🔹 Phosphorus, Potassium, and Other Nutrients

Q19: In what forms is phosphorus taken up by plants?
A19: H₂PO₄⁻ and HPO₄²⁻

Q20: Why is phosphorus often unavailable in soil?
A20: It forms insoluble compounds with Ca at high pH and with Fe/Al at low pH.

Q21: In what form is potassium taken up by plants?
A21: As K⁺ (potassium ion)

Q22: What are two cations important for plant structure and chlorophyll production?
A22: Calcium (Ca²⁺) and Magnesium (Mg²⁺)

Q23: What nutrient is the central atom in the chlorophyll molecule?
A23: Magnesium (Mg²⁺)

Q24: Name two essential macronutrients involved in protein synthesis and energy transfer.
A24: Nitrogen (N) and Phosphorus (P