50 Multiple choice Questions (MCQ) on Agronomy

1. Question: Under the classical Mitscherlich equation, yield increase from added nutrients is best described by:
   A) A linear response to increasing rate
   B) A quadratic plateau response
   C) An exponential rise with diminishing increments
   D) A logistic (sigmoid) curve
   Answer: C
   Rationale: Mitscherlich’s model represents yield response as an exponential saturation—each nutrient increment adds less yield—reflecting the principle of diminishing returns (ScienceDirect, ScienceDirect)

2. Question: Liebig’s law of the minimum differs from Mitscherlich’s law mainly because:
   A) Liebig assumes unlimited nutrient supply
   B) Liebig identifies a single limiting factor, while Mitscherlich defines a diminishing response as supply increases
   C) Liebig focuses only on micronutrients
   D) Liebig describes pest effects on yield
   Answer: B
   Rationale: Liebig identifies the scarcest nutrient as limiting; Mitscherlich adds the idea of diminishing response beyond that minimum.

3. Question: Which yield‑response model reconciles Liebig’s minimum concept with diminishing returns theory?
   A) Quadratic plateau
   B) Logistic growth
   C) Mitscherlich–Baule model
   D) Michaelis–Menten equation
   Answer: C
   Rationale: The Mitscherlich–Baule equation integrates soil reserves and diminishing marginal response, blending Liebig and Mitscherlich.

4. Question: If fertilizer is applied above the agronomic optimum, yield may:
   A) Continue to increase proportionally
   B) Show diminishing returns, plateau, or even decline
   C) Double irrespective of rate
   D) Cease responding immediately
   Answer: B
   Rationale: Beyond optimal N, other constraints take over and extra N may reduce performance.

5. Question: In the classical Mitscherlich equation, the constant c represents:
   A) Soil moisture level
   B) Maximum theoretical yield
   C) Efficiency of nutrient utilization
   D) Risk of crop lodging
   Answer: C
   Rationale: c controls the steepness of response—lower c means slower yield increase per unit nutrient.

6. Question: A land equivalent ratio (LER) greater than 1 implies:
   A) Sole cropping is more productive
   B) Intercropping yields less total production
   C) Intercropping is more efficient per area
   D) Equal area performance as monoculture
   Answer: C
   Rationale: LER = Σ(intercrop yield÷sole crop yield); above 1 means you needed less land to get the same total (or more). (ScienceDirect, MDPI, MDPI, ScienceDirect, Wikipedia)

7. Question: If maize yields 60% and cowpea 40% of their respective sole‑crop outputs when intercropped, LER = 1.0 indicates:
   A) A yield disadvantage
   B) A yield advantage
   C) No land advantage (parity with monoculture)
   D) Miscalculation
   Answer: C
   Rationale: Sum equals 1 means total intercrop yield equals what monoculture would alone have produced—with no land saving.

8. Question: Apparent yield advantage in intercropping often comes from:
   A) Intense crop competition
   B) Resource complementarity (soil, light, root profile)
   C) Pest attraction and control
   D) Higher plant density reducing light
   Answer: B
   Rationale: Different crops use different niches—rooting depth, timing, nutrient patterns—to complement resource capture.

9. Question: In agroforestry, LER is calculated by comparing:
   A) Only tree yield
   B) Only understory crop yield
   C) Combined component yields vs. what both would yield separately
   D) Energy cost per hectare
   Answer: C
   Rationale: Agroforestry LER sums adjusted tree yield + crop yield comparisons against separate sole crops.

10. Question: Which intercropping index adjusts LER for differences in duration (time) of component crops?
    A) LER
    B) Aggressivity index
    C) Area Time Equivalent Ratio (ATER)
    D) Harvest Index
    Answer: C
    Rationale: ATER considers both how much and how long crops occupy land—important for intercropping with differing cycle lengths.

11. Question: The “critical period of weed competition” (CPWC) refers to:
    A) When any weeds must be removed
    B) The developmental window when weeds must be controlled to prevent yield loss
    C) Harvest time only
    D) Only the post‑flowering phase
    Answer: B
    Rationale: CPWC spans from CTWR (crop can first tolerate weeds) to CWFP (late weeds no longer affect final yield) (Wikipedia, MDPI, MDPI, MDPI)

12. Question: In maize, the CPWC most often spans:
    A) Between emergence and the 6‑leaf stage
    B) After grain filling
    C) Only pre‑sowing
    D) During harvest
    Answer: A
    Rationale: Studies typically show V2–V6 as the window when weed interference leads to major losses.

13. Question: If weed control is applied at V2 and again at V4, CPWC is likely:
    A) 50–70 days after emergence
    B) Between leaf stages V2 and V4
    C) Only after flowering
    D) Immediately before harvest
    Answer: B
    Rationale: Those timings bracket the CPWC, where weed pressure must be removed to avoid competition.

14. Question: Crop–weed competition is most intense when weeds:
    A) Emerge after an herbicide
    B) Emerge early, alongside the crop
    C) Are suppressed by the crop canopy
    D) Are perennial
    Answer: B
    Rationale: Early, co‑emerged weeds compete directly for light, nutrients, water.

15. Question: A major reason for weed shifts in cropping systems is:
    A) Continuous monocropping and single‑mode herbicide use
    B) Crop rotation
    C) Certified seed usage
    D) Excessive irrigation
    Answer: A
    Rationale: Without rotation or mode rotation, resistant and opportunistic species dominate over time.

16. Question: A bio‑herbicide differs from a chemical one because it is:
    A) Always broader spectrum
    B) Based on living organisms or their metabolites
    C) Only used pre‑planting
    D) Never requires calibration
    Answer: B
    Rationale: Bio‑herbicides employ microbes or natural toxins that disrupt specific weed growth phases.

17. Question: In Integrated Weed Management (IWM), the most important component is:
    A) Mechanical weed removal only
    B) Combining cultural, mechanical, chemical, and biological tactics
    C) Heavy reliance on residual herbicides
    D) Timing of seed drill
    Answer: B
    Rationale: IWM combines multiple tactics to reduce weed pressure and delay resistance.

18. Question: Allelopathy contributes to weed control by:
    A) Enhancing herbicide absorption
    B) Releasing phytotoxins that suppress neighboring species
    C) Attracting weed predators
    D) Accelerating weed germination
    Answer: B
    Rationale: Many cover and companion crops release compounds inhibiting weed seed germination or growth.

19. Question: A herbicide that affects only young weeds, not the crop, has high:
    A) Applicator toxicity
    B) Residual persistence
    C) Selectivity
    D) Volatility
    Answer: C
    Rationale: Selective herbicides target specific species or growth stages without injuring the crop.

20. Question: Resistance in weeds develops most quickly when:
    A) Crop types are rotated
    B) Herbicide modes are rotated
    C) The same herbicide mode is used repeatedly
    D) IWM is practised
    Answer: C
    Rationale: Repetitive use of one mode of action selects for resistant biotypes over generations.

21. Question: Crop Growth Rate (CGR) is:
    A) Rate of soil dry weight increase
    B) Rate of leaf area decline
    C) Dry matter accumulation per unit ground per time
    D) Transpiration rate per leaf area
    Answer: C
    Rationale: CGR measures canopy performance by indicating biomass increase per hectare per day.

22. Question: Net Assimilation Rate (NAR) measures:
    A) Biomass gain per leaf area
    B) Root mass increase
    C) Soil nutrient depletion
    D) Grain moisture
    Answer: A
    Rationale: NAR = (biomass gain)/(leaf area × time), capturing photosynthetic efficiency per unit leaf

23. Question: Relative Growth Rate (RGR) is:
    A) Absolute weight gain per plant
    B) Biomass gain per initial biomass unit per time
    C) Harvest index minus lodging risk
    D) Crop maturity rate
    Answer: B
    Rationale: RGR = (1/W)(dW/dt), normalizing growth by plant size to compare efficiency across sizes.

24. Question: A breeding ideotype typically features:
    A) Very thick canopy, slow dry‑down
    B) Optimal plant height, root architecture, early maturity
    C) Large seeds only
    D) Only one intensively bred trait
    Answer: B
    Rationale: Ideotype breeding targets multiple traits—architecture, maturity, root depth—to fit a system.

25. Question: Lodging in cereals is least likely if:
    A) Stalk diameter is small
    B) Spike weight is very high
    C) Stalk strength and short stature are balanced
    D) Planting density is extremely high
    Answer: C
    Rationale: Strong, moderately tall stems and balanced spike weight minimize lodging risk.

26. Question: Nutrient Use Efficiency (NUE) is best defined as:
    A) Yield per unit fertilizer applied
    B) Soil nutrient reserve
    C) Plant growth rate
    D) Ratio of water to nutrient uptake
    Answer: A
    Rationale: NUE = output (e.g. kg grain) ÷ input (kg fertilizer)—a metric of fertilizer performance.

27. Question: In India’s Adequate NPK framework, fertilizer rates are based on:
    A) Crop sequence
    B) Soil test results
    C) Reference sufficiency range
    D) All of the above
    Answer: D
    Rationale: Balanced fertilization in India considers crop history, soil test data and established sufficiency ranges.

28. Question: Soil pH below 5.5 mainly affects growth by causing:
    A) Increased phosphorus availability
    B) Aluminum toxicity
    C) Improved microbial activity
    D) Enhanced nitrogen fixation
    Answer: B
    Rationale: Acidic soils solubilize Al³⁺, which inhibits roots and lowers crop performance.

29. Question: Cation Exchange Capacity (CEC) measures:
    A) Soil porosity
    B) Water infiltration rate
    C) Soil’s ability to hold nutrient cations
    D) Weed seed survival
    Answer: C
    Rationale: Higher clay and organic matter increase CEC, allowing soils to store nutrient cations.

30. Question: Liming acid soil primarily:
    A) Adds organic matter
    B) Raises pH and reduces aluminum toxicity
    C) Adds nitrogen
    D) Lowers soil temperature
    Answer: B
    Rationale: Liming neutralizes H⁺ and binds Al³⁺, improving root growth and nutrient availability.

31. Question: Water Use Efficiency (WUE) is defined as:
    A) Irrigation water ÷ crop yield
    B) Grain yield per unit evapotranspiration or water used
    C) Pump hours ÷ yield
    D) Root depth per leaf area
    Answer: B
    Rationale: WUE measures how much yield is produced per unit water consumed (ET), crucial in water-scarce regions.

32. Question: The irrigation scheduling method treating soil water like a “bank account” is:
    A) Bucket model
    B) Water budgeting (checkbook)
    C) Threshold switching
    D) ET-trigger toggling
    Answer: B
    Rationale: Water budgeting tracks inputs (rain/irrigation) and outputs (ET), similar to accounting.

33. Question: Alternate Wetting and Drying (AWD) in rice is:
    A) Continuous flooding
    B) Controlled drying to threshold depth then re‑flooding
    C) No irrigation during vegetative stage
    D) Dry seeding only
    Answer: B
    Rationale: AWD saves water and lowers methane emissions while maintaining yields by allowing soil to dry before re-irrigation (MDPI, MDPI, MDPI, Wikipedia, ScienceDirect, Wikipedia)

34. Question: A PVC perforated tube in AWD is used to:
    A) Apply fertilizer
    B) Monitor subsurface moisture
    C) Measure water table depth
    D) Attract earthworms
    Answer: C
    Rationale: The buried tube shows water depth below surface (usually 15 cm threshold) for irrigation timing.

35. Question: Drip irrigation achieves high efficiency because water is:
    A) Uniformly sprayed overhead
    B) Cooled on leaves to lower ET
    C) Delivered close to roots, minimizing losses
    D) Killing roots beyond zone
    Answer: C
    Rationale: Drip systems reduce evaporation and runoff, allowing precise fertigation in root zone.

36. Question: Distribution Uniformity (DU) refers to:
    A) Evenness of water spread across field
    B) Number of outlets per hectare
    C) Leaf Area Index
    D) Soil sand fraction
    Answer: A
    Rationale: DU measures spread uniformity—typically lowest‑quarter depth ÷ average depth.

37. Question: Soil moisture sensors (tensiometers, capacitance probes) help irrigation scheduling by measuring:
    A) Soil weight
    B) Nutrient concentrations
    C) Water tension or volumetric moisture
    D) Microbial counts
    Answer: C
    Rationale: These instruments provide real-time soil moisture status for precise irrigation decisions.

38. Question: Over‑irrigation may reduce yield due to:
    A) Enhanced nutrient uptake
    B) Nutrient leaching, root oxygen stress, disease, energy waste
    C) Reduced pest pressure
    D) No transpiration
    Answer: B
    Rationale: Excess water leaches nutrients, creates anaerobic soil, fosters disease, and wastes energy.

39. Question: Combining soil moisture and ET‑based methods improves efficiency by:
    A) Increasing waste
    B) Approximately 5–10%
    C) Approximately 15–35% without reducing yield
    D) 100%
    Answer: C
    Rationale: Field trials show integration of both methods reduces water use significantly while preserving yield.

40. Question: ET‑based scheduling relies on:
    A) Relative humidity only
    B) Crop coefficient (Kc) × reference ET × area
    C) Rainfall data only
    D) Soil texture alone
    Answer: B
    Rationale: ET calculators multiply reference ET by Kc (crop stage factor) and field size.

41. Question: Conservation agriculture promotes:
    A) Multiple tillage passes
    B) Continuous monoculture
    C) Zero or reduced tillage, residue retention, crop rotation
    D) No use of cover crops
    Answer: C
    Rationale: Conservation agriculture uses minimal soil disturbance, cover crops, and rotation to improve soil health.

42. Question: Contour ploughing is practiced to:
    A) Improve sun interception
    B) Raise soil pH
    C) Reduce erosion on slopes
    D) Increase tillage frequency
    Answer: C
    Rationale: Ploughing along the slope contour slows runoff and minimizes topsoil loss.

43. Question: The main benefit of crop residue retention is:
    A) More pests
    B) Conservation of moisture, suppression of weeds, erosion control
    C) Slower nutrient cycling
    D) Soil acidification
    Answer: B
    Rationale: Residue cover shields soil from sun and rain, preventing evaporation and erosion.

44. Question: Crop rotation benefits include:
    A) Promoting disease
    B) Enhanced nutrient cycling, pest break, yield stability
    C) Always lower yields
    D) Continuous herbicide needs
    Answer: B
    Rationale: Rotation interrupts pest cycles, balances soil fertility, and supports long‑term productivity.

45. Question: Intercultural operations (weeding, hoeing) across the season:
    A) Are unnecessary when herbicides are used
    B) Improve aeration and reduce weed competition
    C) Always reduce yield
    D) Damage roots if used early
    Answer: B
    Rationale: Mechanical soil stirring can complement other control methods, promoting root respiration and weed removal.

46. Question: Seed quality standards include all except:
    A) Germination percentage
    B) Pure seed weight
    C) Residual moisture content
    D) Tillage pattern
    Answer: D
    Rationale: Tillage practice is not part of seed certification; focus lies on germination, purity, moisture, health.

47. Question: Seed treatment primarily:
    A) Improves weed competition
    B) Protects against seed‑borne pests and diseases
    C) Reduces seed size
    D) Alters soil pH
    Answer: B
    Rationale: Treatments with fungicides/insecticides improve early stand establishment and reduce crop damage.

48. Question: Optimization of row spacing and plant population affects yield when:
    A) Competition for light, water, nutrients becomes limiting
    B) Only root length increases
    C) Seed size varies
    D) Planting is done at night
    Answer: A
    Rationale: Proper spacing maximizes canopy efficiency and resource use among plants.

49. Question: Physiological maturity in seed crops is judged by:
    A) Plant height
    B) Grain moisture content and hardened seed coat
    C) Leaf number
    D) Root depth
    Answer: B
    Rationale: Physiological maturity corresponds to low grain moisture and firm pericarp, minimizing shattering.

50. Question: In hybrid seed production, maternal purity is ensured via:
    A) Hand pollination plus male sterility systems
    B) Seed treatment
    C) Row spacing alone
    D) Irrigation management
    Answer: A
    Rationale: Controlled male sterility and hand‑controlled crosses prevent contamination, ensuring genetic purity.