Soil Science Mini Test (Final Exam) PDF

Multiple Choice Questions - PDF 4.1 24/30 → 80% 1. What is the primary purpose of analyzing soil color? A) To measure the fertility of the soil. B) To classify soils and infer other soil properties. C) To determine the soil's organic matter content. D) To evaluate the water-holding capacity of the...

Multiple Choice Questions - PDF 4.1 24/30 → 80% 1. What is the primary purpose of analyzing soil color? A) To measure the fertility of the soil. B) To classify soils and infer other soil properties. C) To determine the soil's organic matter content. D) To evaluate the water-holding capacity of the soil. 2. What does the Munsell color chart measure? A) Organic content, soil pH, and water retention. B) Texture, structure, and soil compaction. C) Hue, value, and chroma of soil. D) Soil porosity and permeability. 3. What is indicated by the presence of red and brown soil colors? A) High organic matter content. B) Oxidized iron compounds. C) Waterlogged conditions. D) Low fertility. 4. Which soil property is not subject to significant change in the field? A) Soil texture B) Soil color C) Soil organic matter D) Soil structure 5. What are the three major soil textural classes? A) Sandy, clayey, and loamy soils B) Gravelly, silty, and stony soils C) Mineral, organic, and humus soils D) Porous, compacted, and granular soils 6. Which of the following particles has the smallest size range? A) Silt B) Sand C) Clay D) Gravel 7. The largest surface area and adsorption capacity are associated with: A) Sand particles. B) Gravel particles. C) Clay particles. D) Silt particles. 8. What term describes soil particles aggregated into distinct structural units? A) Pores B) Peds C) Textures D) Separates 9. What is the primary factor influencing aggregation in sandy soils? A) Electrostatic forces among clay particles. B) Biological processes involving roots and hyphae. C) Chemical weathering of feldspar minerals. D) The presence of iron and aluminum oxides. 10. Which soil management practice can reduce organic matter and negatively affect soil aggregation over time? A) Adding fertilizers. B) Using no-till techniques. C) Frequent tillage. D) Irrigation. 11. Which process is essential in determining soil texture in the lab? A) Sieving B) Oxidation C) Hydration D) Compaction 12. Stokes' Law is used to determine: A) Soil color. B) Soil particle density. C) The settling velocity of soil particles. D) Soil organic content. 13. What is the major difference in aggregation between tropical and temperate soils? A) Tropical soils depend more on organic matter. B) Tropical soils rely more on iron/aluminum oxides for stability. C) Temperate soils have greater aggregate stability. D) Both tropical and temperate soils have similar aggregation factors. 14. What is the name of the soil textural class containing 15% sand, 15% clay, and 70% silt? A) Loam B) Sandy loam C) Silty clay D) Silt loam 15. Which type of soil structure is most common in B horizons? A) Granular B) Prismatic C) Single-grained D) Platelike 16. Which factor has the greatest influence on soil structure in sandy soils? A) High levels of organic matter. B) Iron oxide coatings. C) Root and fungal activity. D) Clay aggregation. 17. What does a soil with "massive" structure indicate? A) Excellent drainage and aeration. B) Poorly aggregated soil with no visible peds. C) High organic matter content. D) Strong aggregation and stability. 18. Which of the following influences the stability of soil aggregates? A) Organic matter B) Clay content C) Iron and aluminum oxides D) All of the above 19. The "feel" method for determining soil texture relies on which property? A) Soil color B) Soil structure C) Soil particle size D) Soil organic matter content 20. Why are soils high in organic matter more stable? A) They are less porous. B) They resist disintegration when wet. C) They have higher iron oxide content. D) They contain larger clay particles. 21. What are "glomalin" glycoproteins primarily associated with? A) Clay particles B) Organic matter breakdown C) Soil fungi aggregation D) Iron oxide stabilization 22. Which soil horizon typically exhibits granular structure? A) A horizon B) B horizon C) C horizon D) E horizon 23. Which cation promotes the flocculation of clay particles? A) Na+ B) K+ C) Ca2+ D) Cl- 24. What is the effect of monovalent cations like Na+ on soil structure? A) Promote aggregation. B) Cause clay particles to repel each other. C) Enhance soil organic matter. D) Neutralize soil pH. 25. Which tool is used in particle-size analysis to measure suspended soil particles? A) Microscope B) Hydrometer C) Laser diffraction device D) Sieving apparatus 26. Which of the following processes does not influence soil aggregation? A) Tillage B) Erosion C) Crop rotation D) Volume changes in clay 27. What does the term "pseudosand" refer to in tropical soils? A) Organic matter-bound sand particles. B) Aggregates stabilized by iron oxides. C) Large gravel-like soil particles. D) Artificially mixed sandy soil. 28. In soil particle-size distribution, what is the primary component of clay? A) Silica minerals. B) Iron oxides. C) Secondary silicates. D) Organic polymers. 29. Which soil structure type often occurs in poorly drained soils in humid regions? A) Columnar B) Platelike C) Granular D) Blocky 30. What is the primary cause of blue and gray colors in soil? A) High organic matter. B) Oxidation of iron. C) Reduced iron in anaerobic conditions. D) High clay content. Multiple Choice Questions - PDF 4.2 20/30 → 67% 1. What is "soil tilth"? A) The chemical composition of soil. B) The physical condition of soil in relation to plant growth. C) The ability of soil to retain water. D) The organic matter content in soil. 2. Which factor does not contribute to good soil tilth? A) Aggregate stability. B) Bulk density. C) High salinity. D) Soil aeration. 3. What does "soil friability" refer to? A) The soil's ability to retain nutrients. B) The ease with which soil clods crumble. C) The water infiltration rate in soil. D) The organic matter content in soil. 4. What tool is commonly used for conventional tillage? A) No-till planter. B) Disc harrow. C) Moldboard plow. D) Subsoiler. 5. Which type of tillage is most effective in minimizing soil erosion? A) Conventional tillage. B) Conservation tillage. C) Strip tillage. D) Deep tillage. 6. What causes soil crusting during heavy rain? A) High organic matter content. B) Dispersion of fine soil particles. C) Increased aggregate stability. D) Sandy soil composition. 7. Which soil conditioner improves physical soil structure by promoting flocculation? A) Urea. B) Gypsum. C) Sulfur. D) Phosphate. 8. What does soil "particle density" exclude? A) The mass of soil solids. B) The volume of pore spaces. C) The specific gravity of soil. D) The crystal structure of minerals. 9. Which soil property is influenced by soil bulk density? A) Particle size. B) Pore space. C) Organic matter content. D) Specific gravity. 10. How does compaction affect soil bulk density? A) Increases bulk density. B) Reduces bulk density. C) Has no effect on bulk density. D) Alters soil particle density. 11. What is the primary benefit of macropores in soil? A) Storing water for plant use. B) Providing habitat for microorganisms. C) Facilitating air and water movement. D) Reducing bulk density. 12. Micropores in soil are typically: A) Larger than 0.08 mm. B) Smaller than 0.08 mm. C) Filled with air in moist soils. D) Responsible for rapid water drainage. 13. Which clay mineral is associated with high swelling potential? A) Kaolinite. B) Smectite. C) Illite. D) Montmorillonite. 14. What is the "angle of repose" in soil science? A) The steepest angle a soil can hold without slumping. B) The optimal angle for water infiltration. C) The angle formed by compacted soil aggregates. D) The slope angle necessary for plant growth. 15. Which type of soil strength test measures soil resistance to penetration? A) Proctor test. B) Compression test. C) Consistence test. D) Penetrometer test. 16. Which soil texture is most prone to compaction? A) Sandy soils. B) Clayey soils. C) Loamy soils. D) Gravelly soils. 17. What happens to bulk density when soil is compacted? A) It decreases. B) It remains the same. C) It increases. D) It fluctuates randomly. 18. What is the main drawback of subsoiling in compacted clay soils? A) It increases soil organic matter. B) It is energy-intensive and temporary. C) It does not improve water infiltration. D) It only works in sandy soils. 19. Which type of tillage minimizes soil disturbance while maintaining crop residues? A) Deep tillage. B) Strip tillage. C) Conventional tillage. D) No-till. 20. What is the purpose of the Proctor test? A) To measure soil organic matter. B) To determine soil bulk density. C) To find the optimal moisture content for compaction. D) To test the soil's permeability. 21. What is thixotropy in soils? A) Soil hardening when dry. B) Sudden liquefaction of a wet soil mass under vibration. C) Soil swelling due to organic matter. D) Soil compaction from heavy machinery. 22. What is the main cause of structural damage in soils during wet conditions? A) High aggregate stability. B) Low soil organic matter. C) Field capacity moisture content. D) Increased compaction pressure. 23. What are the Atterberg Limits used to measure? A) Soil bulk density and porosity. B) Soil plasticity and moisture content. C) Soil nutrient availability. D) Soil organic matter levels. 24. What type of soil deformation is described by the term "soil creep"? A) Rapid landslides on wet slopes. B) Gradual downslope movement of soil. C) Horizontal cracking due to swelling. D) Sudden collapse under weight. 25. Which type of clay is least prone to swelling? A) Smectite. B) Illite. C) Kaolinite. D) Montmorillonite. 26. Which type of pore is too small for bacterial entry? A) Macropores. B) Micropores. C) Nanopores. D) Biopores. 27. Which practice increases soil bulk density in forests? A) Mulching. B) Logging with heavy equipment. C) Selective cutting. D) Growing taprooted cover crops. 28. Which material is commonly added to improve the stability of acidic soils? A) Sulfur. B) Calcium carbonate (lime). C) Gypsum. D) Phosphorus. 29. What is a major disadvantage of expansive soils? A) High permeability. B) Poor drainage. C) Severe damage to foundations and pavements. D) Low fertility. 30. How do biopores benefit soil structure? A) Enhance soil compaction. B) Provide pathways for air and water movement. C) Increase soil bulk density. D) Eliminate micropores. Multiple Choice Test on Nitrogen and Soil Economy Part 1: Basics of Nitrogen in Soils 1. What is the primary form of nitrogen in the atmosphere? A) NH₄⁺ (ammonium) B) NO₃⁻ (nitrate) C) N₂ (dinitrogen gas) D) NO₂⁻ (nitrite) 2. Why is nitrogen essential for plants? A) It is a key component of carbohydrates. B) It helps in the uptake of phosphorus. C) It is integral to amino acids and nucleic acids. D) It regulates water movement in plants. 3. What percentage of nitrogen do healthy plant leaves typically contain? A) 0.5–1.0% B) 2.0–4.0% C) 5.0–7.0% D) 7.0–10.0% 4. Which symptom is associated with nitrogen deficiency in plants? A) Purple spots on leaves B) Chlorosis (yellowing of leaves) C) Excessive fruit production D) Rapid growth 5. What happens when there is an oversupply of nitrogen to plants? A) Stunted root growth B) Increased susceptibility to disease C) Early maturation D) Reduction in leaf size Part 2: Nitrogen Transformations in Soils 6. What is the process of converting organic nitrogen to ammonium called? A) Denitrification B) Immobilization C) Mineralization D) Nitrification 7. What is nitrification? A) Conversion of ammonium to nitrate B) Fixation of atmospheric nitrogen into the soil C) Conversion of nitrate to nitrogen gas D) Absorption of nitrogen by plant roots 8. Which bacteria genus is responsible for converting ammonium to nitrite? A) Nitrobacter B) Rhizobium C) Nitrosomonas D) Azotobacter 9. What is denitrification? A) Loss of nitrogen through leaching B) Reduction of nitrate to nitrogen gases C) Conversion of ammonium to nitrate D) Fixation of nitrogen gas into organic forms 10. Which condition promotes denitrification? A) High oxygen levels B) Dry soil C) Waterlogged, anaerobic soil D) Low organic matter Part 3: Nitrogen Fixation and Cycling  11. Which microorganism group is primarily responsible for biological nitrogen fixation? A) Fungi B) Archaea C) Cyanobacteria D) Actinomycetes 12. What is the primary product of biological nitrogen fixation? A) Ammonium B) Nitrate C) Nitrite D) Organic nitrogen 13. What percentage of soil nitrogen is typically found in organic forms? A) 1–2% B) 10–20% C) 50–60% D) 95–99% 14. How does nitrogen contribute to the protein content of plants? A) It is a primary component of chlorophyll. B) It is part of the amino acids that form proteins. C) It acts as a catalyst for enzyme activity. D) It regulates photosynthetic pathways. 15. What is the dominant form of nitrogen lost to leaching? A) Ammonium B) Nitrite C) Nitrate D) Organic nitrogen Part 4: Environmental Impacts of Nitrogen 16. What environmental problem is caused by excess nitrate in groundwater? A) Eutrophication B) Algal blooms C) Groundwater pollution D) Acid rain 17. How does nitrous oxide (N₂O) impact the atmosphere? A) Depletes ozone and contributes to climate change B) Increases carbon dioxide levels C) Enhances photosynthesis rates D) Reduces methane emissions 18. What agricultural practice can reduce nitrogen runoff? A) Over-fertilizing B) No-till farming C) Frequent tillage D) Applying fertilizers to bare soils 19. Which condition exacerbates ammonia volatilization from soils? A) Low pH B) High organic matter C) High soil temperature and pH D) Low ammonium concentrations 20. What is the major source of nitrogen for terrestrial ecosystems? A) Atmospheric deposition B) Chemical fertilizers C) Biological nitrogen fixation D) Leaching from subsoils Part 5: Nitrogen Management in Soils 21. How can nitrogen losses through leaching be minimized? A) Frequent irrigation B) Deep placement of fertilizers C) Increasing soil pH D) Adding excess ammonium fertilizers 22. What happens during ammonium fixation in clay soils? A) Ammonium becomes exchangeable. B) Ammonium is strongly adsorbed in clay layers. C) Ammonium is volatilized into gas. D) Ammonium is oxidized to nitrate. 23. Which soil condition favors nitrification? A) Anaerobic environment B) High soil moisture C) Well-drained, aerobic soils D) Low calcium and magnesium levels 24. What is the purpose of incorporating fertilizers into the soil? A) To reduce ammonia volatilization B) To prevent water infiltration C) To enhance microbial activity D) To lower soil temperature 25. Which management practice can enhance biological nitrogen fixation? A) Applying synthetic nitrogen fertilizers B) Growing leguminous crops C) Increasing tillage frequency D) Adding chemical inhibitors Part 6: Advanced Nitrogen Processes 26. What is anammox? A) Conversion of ammonium to nitrate B) Oxidation of ammonium to dinitrogen gas C) Fixation of atmospheric nitrogen D) Reduction of nitrate to ammonium 27. Which compound is responsible for immobilization of mineral nitrogen in soils? A) Low C/N ratio residues B) High C/N ratio residues C) Soluble organic nitrogen D) Ammonium nitrate  28. What is the role of mycorrhizal fungi in nitrogen uptake? A) Fix atmospheric nitrogen B) Enhance nitrate absorption C) Improve uptake of organic nitrogen D) Convert nitrate to ammonium 29. Which of the following increases soil acidity during nitrogen transformations? A) Denitrification B) Nitrification C) Ammonium fixation D) Mineralization 30. How does soil organic matter affect nitrogen cycling? A) It inhibits microbial activity. B) It promotes nitrogen mineralization. C) It reduces ammonium fixation. D) It enhances ammonia volatilization. Phosphorus: 30 Questions 1. Why is phosphorus considered a critical nutrient for plants? A) It is vital for chlorophyll synthesis. B) It is a component of DNA, RNA, and ATP. C) It regulates photosynthesis. D) It is the main source of plant proteins. 2. What is a key symptom of phosphorus deficiency in plants? A) Pale yellow leaves. B) Purple or dark bluish-green leaves. C) Wilted roots. D) Spotted stems. 3. How do mycorrhizal fungi assist plants in phosphorus uptake? A) By synthesizing phosphorus. B) By breaking down soil organic matter. C) By extending root absorption zones through their hyphae. D) By converting phosphorus into nitrogen. 4. What is the major issue with phosphorus fertilizers in tropical soils? A) They are rapidly leached into groundwater. B) They react with aluminum and iron, becoming insoluble. C) They are toxic to plant roots. D) They evaporate under high temperatures. 5. What does eutrophication primarily result from? A) Excessive nitrogen in soil. B) High phosphorus runoff into water bodies. C) Soil acidification. D) Potassium toxicity. 6. Which form of phosphorus is most readily available for plant uptake? A) Organic phosphorus in residues. B) Calcium-bound phosphorus. C) Phosphate ions in soil solution. D) Aluminum-phosphate complexes. 7. In what form is phosphorus most commonly found in alkaline soils? A) Calcium phosphates. B) Iron phosphates. C) Aluminum phosphates. D) Organic phosphates. 8. Which soil property most limits phosphorus availability? A) Bulk density. B) Cation exchange capacity. C) Soil pH. D) Soil texture. 9. What proportion of soil phosphorus is typically found in the soil solution? A) 0.001–1 mg/L. B) 10–20 mg/L. C) 100–200 mg/L. D) 500–1000 mg/L. 10. What happens during phosphorus fixation in soils? A) Phosphorus is converted to organic matter. B) Phosphorus is volatilized. C) Soluble phosphorus forms insoluble compounds. D) Phosphorus undergoes leaching. 11. What percentage of applied phosphorus is usually taken up by plants in the first year? A) 10–15%. B) 25–30%. C) 40–50%. D) 60–70%. 12. Which practice can help reduce phosphorus runoff? A) Over-application of fertilizers. B) No-till farming techniques. C) Intensive grazing. D) Continuous monocropping. 13. What role does phosphorus play in biological nitrogen fixation? A) It inhibits nodulation. B) It is necessary for energy transfer in fixation processes. C) It accelerates decomposition of nitrogen residues. D) It neutralizes ammonia toxicity. 14. Which plant nutrient uptake process is slowed by phosphorus deficiency? A) Potassium translocation. B) Nitrogen assimilation. C) Calcium absorption. D) Sulfur fixation. 15. How does soil pH affect phosphorus availability? A) High pH increases availability. B) Low pH decreases fixation. C) Neutral pH optimizes availability. D) pH has no effect. 16. What causes the purple pigmentation in phosphorus-deficient plants? A) Chlorophyll breakdown. B) Carotenoid synthesis. C) Accumulation of anthocyanins. D) Overproduction of ATP. 17. Which form of phosphorus is dominant in highly weathered tropical soils? A) Organic phosphorus B) Calcium-bound phosphorus C) Iron and aluminum-bound phosphorus D) Soluble phosphorus 18. What is the effect of long-term phosphorus saturation in soils? A) It increases soil erosion. B) It leads to environmental pollution. C) It depletes soil organic matter. D) It improves nitrogen fixation. 19. Which phosphorus-containing compound is most insoluble in neutral soils? A) Strengite B) Fluorapatite C) Calcium phosphate D) Nucleic acids 20. How can phosphorus fixation be minimized in soils? A) Applying fertilizers during the dry season B) Incorporating organic matter C) Using deep tillage methods D) Lowering soil temperature 21. What is a major source of phosphorus pollution in lakes and rivers? A) Urban sewage outflows B) Excessive potassium application C) Eroded sediments carrying particulate phosphorus D) Volatilization from agricultural soils 22. What is the role of phosphatases secreted by plant roots? A) To increase nitrogen fixation B) To mobilize organic phosphorus C) To fix phosphorus into soil minerals D) To reduce phosphorus leaching 23. In the phosphorus cycle, what is the primary transformation that replenishes soil solution phosphorus? A) Adsorption B) Immobilization C) Mineralization D) Leaching 24. What is the dominant phosphorus ion in soils with a pH of 5? A) H3PO4 B) H2PO4- C) HPO4²- D) PO4³- 25. Which farming practice can help improve phosphorus availability to crops? A) Rotational grazing B) Incorporating crop residues C) Continuous monocropping D) Heavy irrigation 26. What does "luxury consumption" of phosphorus refer to in plants? A) Storing excess phosphorus for future use B) Wasting phosphorus through leaching C) Over-uptake of phosphorus beyond immediate needs D) Dependency on fertilizers 27. What percentage of soil phosphorus is typically present in organic forms? A) 5-10% B) 20-80% C) 50-90% D) 90-95% 28. How does phosphorus help in photosynthesis? A) By forming chlorophyll molecules B) By activating ATP synthesis C) By increasing leaf area D) By regulating carbon dioxide uptake 29. What is a characteristic of phosphorus-rich wastewater? A) It is highly alkaline. B) It is rich in organic phosphorus. C) It contains high levels of particulate phosphorus. D) It is highly acidic. 30. Which type of phosphorus contributes least to plant nutrition? A) Organic phosphorus B) Adsorbed phosphorus C) Calcium-bound phosphorus D) Aluminum-bound phosphorus Potassium: 30 Questions 1. What is the primary function of potassium in plants? A) Building proteins and DNA. B) Regulating stomatal function and water uptake. C) Forming plant cell walls. D) Fixing atmospheric nitrogen. 2. Which symptom indicates potassium deficiency in plants? A) Yellowing of older leaves. B) Purple stems. C) Interveinal chlorosis and leaf edge necrosis. D) Stunted growth with red veins. 3. What form of potassium is most available to plants? A) K+ ions in the soil solution. B) Potassium bound to clay minerals. C) Potassium in organic residues. D) Potassium oxides. 4. Which soil type is likely to have the highest potassium reserves? A) Sandy soils. B) Clay soils. C) Peaty soils. D) Loamy soils. 5. How does potassium affect drought resistance in plants? A) By strengthening leaf cuticles. B) By enhancing root expansion. C) By regulating stomatal closure to reduce water loss. D) By increasing transpiration rates. 6. Which agricultural practice depletes potassium most rapidly? A) Continuous tillage. B) Heavy irrigation. C) Overgrazing. D) Harvesting high-yield crops without replenishment. 7. What is the dominant source of potassium in soils? A) Organic matter decomposition. B) Weathering of potassium-bearing minerals. C) Fertilizer application. D) Atmospheric deposition. 8. Which potassium fertilizer contains the highest K content? A) Potassium sulfate. B) Potassium nitrate. C) Potassium chloride. D) Potassium carbonate. 9. Which soil process makes potassium less available to plants? A) Fixation in clay interlayers. B) Adsorption by organic matter. C) Nitrification. D) Phosphorus precipitation. 10. What is the typical potassium concentration in plant tissues? A) 0.1–0.3%. B) 1–3%. C) 10–15%. D) 20–30%. 11. How is potassium lost from agricultural soils? A) Leaching in coarse-textured soils. B) Conversion to organic potassium. C) Volatilization during tillage. D) Adsorption on clay surfaces. 12. What soil condition enhances potassium leaching? A) High organic matter. B) Low clay content. C) High cation exchange capacity. D) Alkaline pH. 13. How does potassium improve crop quality? A) By enhancing photosynthetic pigments. B) By increasing sugar and starch content. C) By accelerating flowering and fruiting. D) By reducing water usage. 14. Why is potassium referred to as the "luxury nutrient"? A) Plants take up more potassium than they need. B) It is expensive to supply. C) It provides long-term storage in plants. D) It is rarely required in fertilizers. 15. What is the role of exchangeable potassium in soils? A) It forms insoluble compounds. B) It is the reserve pool for plant uptake. C) It catalyzes nutrient fixation. D) It leaches easily from soils. 16. How does potassium affect the osmotic balance in plants? A) By decreasing transpiration rates B) By maintaining turgor pressure C) By inhibiting enzyme activity D) By increasing chlorophyll synthesis 17. Which potassium pool is most available to plants? A) Exchangeable potassium B) Fixed potassium C) Mineral potassium D) Leached potassium 18. What causes potassium fixation in soils? A) Leaching into groundwater B) Adsorption on organic matter C) Intercalation in clay mineral layers D) Reaction with calcium carbonate 19. What role does potassium play in enzyme activation? A) It directly forms enzyme structures. B) It acts as a cofactor for enzyme activity. C) It inhibits enzyme denaturation. D) It reduces enzyme sensitivity to pH changes. 20. What is the potassium concentration in soil solution under normal conditions? A) 1-2 mg/L B) 5-10 mg/L C) 50-100 mg/L D) 200-500 mg/L 21. What type of soil is most prone to potassium leaching? A) Sandy soils B) Clay soils C) Loamy soils D) Silty soils 22. How does potassium improve disease resistance in plants? A) By strengthening root exudates B) By enhancing cell wall integrity C) By inhibiting pathogen enzymes D) By increasing chlorophyll production 23. Which crop is most likely to experience potassium deficiency? A) Corn B) Soybeans C) Potatoes D) Grapes 24. What happens when potassium is over-applied? A) It reduces soil pH drastically. B) It leads to calcium and magnesium deficiencies. C) It causes rapid nitrogen volatilization. D) It inhibits phosphorus uptake. 25. Which mineral is a natural source of potassium in soils? A) Gypsum B) Feldspar C) Calcite D) Quartz 26. What is the main disadvantage of potassium chloride as a fertilizer? A) It has a low potassium content. B) It is water-insoluble. C) It can increase soil salinity. D) It is prone to leaching. 27. How does potassium contribute to crop quality? A) Enhances flavor and sugar content. B) Promotes early flowering. C) Increases protein synthesis. D) Boosts nitrogen absorption. 28. Which practice enhances potassium availability in soils? A) Deep tillage B) Liming acidic soils C) Adding high-sodium fertilizers D) Continuous irrigation 29. How does potassium affect plant water use? A) Increases transpiration rates B) Reduces water loss through stomata C) Promotes excess water uptake D) Alters water absorption pathways 30. What is the typical potassium content in crop residues? A) 0.1-0.5% B) 1-3% C) 5-7% D) 10-15% Chapter 8-1 What is the primary characteristic of soil colloids? a. Large particle size b. High reactivity due to surface area and charges c. Complete absence of nutrients d. Low water-holding capacity Answer: b Which type of soil colloid is primarily organic in nature? a. Crystalline silicate clays b. Noncrystalline silicate clays c. Humus d. Iron and aluminum oxides Answer: c What structure characterizes 2:1 silicate clays? a. One tetrahedral sheet and one octahedral sheet b. Two tetrahedral sheets with one octahedral sheet in between c. Non-layered amorphous structure d. A single layer of crystalline sheets Answer: b What is the primary source of permanent charge in soil colloids? a. pH changes b. Isomorphous substitution c. Adsorption of cations d. Water retention Answer: b Which soil colloid is most likely to exhibit swelling and shrinkage? a. Kaolinite b. Smectite c. Gibbsite d. Humus Answer: b What happens to the negative charges on colloids as pH increases? a. They increase b. They decrease c. They remain the same d. They turn into positive charges Answer: a Answers 4.1 B - To classify soils and infer other soil properties. C - Hue, value, and chroma of soil. A - Soil texture. A - Sandy, clayey, and loamy soils. C - Clay. B - Their size and the viscosity of water. B - Spheroidal. B - Biological processes involving roots and hyphae. C - Frequent tillage. B - Tropical soils rely more on iron/aluminum oxides for stability. A - Sieving. C - The settling velocity of soil particles. B - Tropical soils rely more on iron/aluminum oxides for stability. D - Silt loam. B - Prismatic. C - Root and fungal activity. B - Poorly aggregated soil with no visible peds. D - All of the above. C - Soil particle size. B - They resist disintegration when wet. C - Soil fungi aggregation. A - A horizon. C - Ca²⁺. B - Cause clay particles to repel each other. B - Hydrometer. D - Volume changes in clay. B - Aggregates stabilized by iron oxides. C - Secondary silicates. B - Platelike. C - Reduced iron in anaerobic conditions.