Certified Crop Adviser (CCA) International Exam — Questions and Answers

Question 1: What is the main form of nitrogen taken up by most crops from the soil?

Ammonium and nitrate (Correct answer)
Organic nitrogen
Dinitrogen gas
Urea

Correct answer: Ammonium and nitrate

Most crops absorb nitrogen primarily as ammonium (NH4+) and nitrate (NO3-) ions from the soil solution.

Question 2: In sprinkler irrigation design, what does 'distribution uniformity' measure?

The pressure at the pump
How evenly water is applied across the irrigated area (Correct answer)
The slope of the irrigated field
The discharge rate of individual emitters

Correct answer: How evenly water is applied across the irrigated area

Distribution uniformity measures how evenly water is spread across the field, with high uniformity ensuring all areas receive adequate amounts without over- or under-irrigation.

Question 3: What is the main purpose of a grassed waterway in a crop field?

Increase field drainage for early planting
Safely convey concentrated surface runoff without causing erosion (Correct answer)
Supply water to drip irrigation systems
Provide habitat for beneficial insects

Correct answer: Safely convey concentrated surface runoff without causing erosion

Grassed waterways are channels planted with grass that carry concentrated runoff from sloping fields to an outlet without eroding the channel bottom or sides.

Question 4: What does the term 'base saturation' refer to in soil science?

Ratio of sand to clay
Percentage of CEC occupied by base cations (Correct answer)
Depth of the A horizon
Total amount of organic matter

Correct answer: Percentage of CEC occupied by base cations

Base saturation is the percentage of a soil's CEC occupied by basic cations such as Ca²⁺, Mg²⁺, K⁺, and Na⁺.

Question 5: Open-pollinated varieties differ from hybrid varieties primarily because they do what?

Always outyield commercial hybrids
Breed true from saved seed and maintain genetic consistency (Correct answer)
Produce sterile seeds
Require cross-pollination each season

Correct answer: Breed true from saved seed and maintain genetic consistency

Open-pollinated varieties are genetically stable populations that breed true when seed is saved and replanted, unlike hybrids which segregate in F2.

Question 6: Soybean cyst nematode (SCN) is best managed long-term using what strategy?

Deep tillage to bury cysts
Rotating SCN-susceptible and resistant soybean varieties combined with crop rotation (Correct answer)
Flooding fields during fallow
Annual nematicide application

Correct answer: Rotating SCN-susceptible and resistant soybean varieties combined with crop rotation

Combining SCN-resistant varieties with rotation to non-host crops (corn) reduces SCN population densities and extends the effectiveness of resistance genes.

Question 7: GMO crops produced using Agrobacterium-mediated transformation are transformed how?

By chemical mutagenesis of pollen
By inserting foreign DNA via the Ti plasmid into plant cells (Correct answer)
By exposing seeds to radiation
By grafting onto transgenic rootstocks

Correct answer: By inserting foreign DNA via the Ti plasmid into plant cells

Agrobacterium tumefaciens naturally transfers its Ti plasmid DNA into plant cells; scientists exploit this to insert desired genes.

Question 8: What is the term for the number of days from planting to physiological maturity in corn?

Vernalization period
Growing degree days (GDD) accumulation
Dormancy period
Relative maturity rating (Correct answer)

Correct answer: Relative maturity rating

Relative maturity (RM) rating estimates the number of days for a corn hybrid to reach maturity under standard growing conditions.

Question 9: What is the primary function of phosphorus in plant nutrition?

Chlorophyll synthesis
Disease resistance
Water regulation
Energy transfer and root development (Correct answer)

Correct answer: Energy transfer and root development

Phosphorus is critical for ATP synthesis, energy transfer, and promoting root and seed development.

Question 10: What is photorespiration in crop plants?

Cellular respiration that is accelerated by light
A wasteful process where RuBisCO fixes O2 instead of CO2 (Correct answer)
Light-dependent ATP production in mitochondria
Photosynthesis that occurs during respiration

Correct answer: A wasteful process where RuBisCO fixes O2 instead of CO2

Photorespiration occurs when RuBisCO binds oxygen instead of CO2, releasing previously fixed carbon as CO2 without producing useful sugars, reducing yield.

Question 11: What is the primary mechanism by which glyphosate kills plants?

Destroys cell membranes upon contact
Inhibits the EPSPS enzyme in the shikimate pathway, blocking aromatic amino acid synthesis (Correct answer)
Disrupts photosynthesis by blocking chlorophyll synthesis
Prevents mitosis in actively dividing cells

Correct answer: Inhibits the EPSPS enzyme in the shikimate pathway, blocking aromatic amino acid synthesis

Glyphosate inhibits the EPSPS enzyme in the shikimate pathway, preventing plants from producing essential aromatic amino acids needed for protein synthesis and growth.

Question 12: What is precision agriculture primarily designed to do?

Replace all labor with fully autonomous robots
Apply inputs variably across a field based on spatial variability to optimize efficiency and reduce waste (Correct answer)
Increase maximum pesticide application rates
Standardize all field management to one average rate

Correct answer: Apply inputs variably across a field based on spatial variability to optimize efficiency and reduce waste

Precision agriculture uses GPS, sensors, and data analytics to apply fertilizers, pesticides, and water at variable rates matching the needs of different zones within a field.

Question 13: Which process describes the loss of water vapor from plant leaves primarily through stomata?

Transpiration (Correct answer)
Osmosis
Guttation
Imbibition

Correct answer: Transpiration

Transpiration is the evaporation of water from plant surfaces through stomata, which creates a water potential gradient that drives water uptake from the soil.

Question 14: What does heritability (h²) measure in a plant breeding context?

The proportion of total phenotypic variation due to genetic variation (Correct answer)
The dominance relationship between alleles
The number of genes controlling a trait
The probability a trait is inherited by all offspring

Correct answer: The proportion of total phenotypic variation due to genetic variation

Heritability estimates the fraction of observed variation in a trait that is attributable to genetic differences rather than environmental factors.

Question 15: Which micronutrient deficiency commonly appears as interveinal chlorosis on young leaves?

Manganese
Zinc
Iron (Correct answer)
Boron

Correct answer: Iron

Iron deficiency causes interveinal chlorosis on young leaves because iron is immobile in plants.

Question 16: Which irrigation scheduling method uses crop canopy temperature to detect plant water stress?

Gravimetric soil sampling
Electrical resistance blocks
Neutron probe monitoring
Infrared thermometry (crop water stress index) (Correct answer)

Correct answer: Infrared thermometry (crop water stress index)

The crop water stress index (CWSI) uses infrared thermometers to measure canopy temperature, since stressed plants close stomata and become warmer than well-watered plants.

Question 17: Which factor most limits soybean yield in humid temperate climates?

Excess nitrogen fertilization
Low atmospheric CO₂ concentration
Drought stress during the reproductive period (Correct answer)
Extreme heat during vegetative stages

Correct answer: Drought stress during the reproductive period

Soybean is most sensitive to water stress during flowering and pod fill, which directly reduces pod set and seed size.

Question 18: What is the field capacity of a soil?

The minimum water content at which a plant can survive
The soil water content after free drainage has ceased following saturation (Correct answer)
The total pore space volume of the soil
The maximum depth of water that can infiltrate in one hour

Correct answer: The soil water content after free drainage has ceased following saturation

Field capacity is the soil moisture content remaining after excess water has drained under gravity, representing the upper limit of plant-available water.

Question 19: Which irrigation efficiency improvement method involves applying water at precise times and small amounts based on sensor data?

Precision irrigation using soil moisture sensor networks (Correct answer)
Scheduled flood irrigation
Annual irrigation calendar scheduling
Manual furrow adjustment

Correct answer: Precision irrigation using soil moisture sensor networks

Precision irrigation uses real-time soil moisture sensor data to trigger small, frequent water applications that match crop demand, maximizing efficiency.

Question 20: What is the primary purpose of crop rotation in agronomic systems?

Break pest and disease cycles and improve soil health (Correct answer)
Simplify harvest scheduling
Increase machinery efficiency
Reduce labor requirements

Correct answer: Break pest and disease cycles and improve soil health

Rotating crops disrupts the life cycles of pathogens, insects, and weeds that are host-specific, while diversifying soil nutrient demands.

Question 21: What does 'nutrient management planning' require farmers to document?

Soil test results, nutrient sources, application rates, timing, and methods to match crop needs while protecting water quality (Correct answer)
Only the types of fertilizers purchased each year
Pesticide purchase and storage records only
Monthly water usage and irrigation records

Correct answer: Soil test results, nutrient sources, application rates, timing, and methods to match crop needs while protecting water quality

A nutrient management plan documents soil testing, planned nutrient applications, timing, placement, and quantities to optimize crop production and protect the environment.

Question 22: What is the primary cause of soil salinity buildup in irrigated fields in arid regions?

Excessive use of manure fertilizers
Salt accumulation from irrigation water combined with inadequate leaching (Correct answer)
Organic matter decomposition releasing salts
High rainfall dissolving rock minerals

Correct answer: Salt accumulation from irrigation water combined with inadequate leaching

Irrigation water carries dissolved salts that accumulate in the root zone as water evaporates or is transpired, especially in arid climates with insufficient rainfall to leach salts.

Question 23: A field with hardpan soil would most likely suffer from which problem?

Rapid organic matter buildup
High cation exchange capacity
Poor drainage and restricted root growth (Correct answer)
Excess nitrogen leaching

Correct answer: Poor drainage and restricted root growth

Hardpan is a dense, compacted soil layer that restricts water drainage and prevents roots from penetrating deeper soil layers.

Question 24: Polyploidy in plants refers to what condition?

Having chromosomes of unequal size
Lacking a nucleus in mature cells
Having only one set of chromosomes
Having more than two complete sets of chromosomes (Correct answer)

Correct answer: Having more than two complete sets of chromosomes

Polyploidy is the condition of having three or more complete sets of chromosomes; it is common in many important crop plants like wheat and cotton.

Question 25: Palmer amaranth is considered one of the most problematic weeds in US row crops primarily because of what?

It only affects organic fields
It has evolved resistance to multiple herbicide modes of action and grows extremely fast (Correct answer)
It is a C3 plant with slow growth
It produces few seeds per plant

Correct answer: It has evolved resistance to multiple herbicide modes of action and grows extremely fast

Palmer amaranth grows up to 2–3 inches per day, produces hundreds of thousands of seeds, and has developed resistance to herbicides including glyphosate.

Question 26: Which practice helps reduce lodging in small grain crops such as wheat?

Avoiding all nitrogen fertilizer
Increasing seeding rate
Applying plant growth regulators (Correct answer)
Deep irrigation

Correct answer: Applying plant growth regulators

Plant growth regulators (PGRs) shorten and strengthen straw internodes, reducing the risk of lodging in wheat and other small grains.

Question 27: Which soil horizon is typically referred to as the 'topsoil'?

B horizon
O horizon
C horizon
A horizon (Correct answer)

Correct answer: A horizon

The A horizon is the topsoil layer, rich in organic matter and biological activity, and most important for crop production.

Question 28: What is the primary purpose of a cover crop in an agronomic rotation?

Maximize cash crop yield
Protect and improve soil between cash crop seasons (Correct answer)
Increase soil salinity
Eliminate need for fertilizer permanently

Correct answer: Protect and improve soil between cash crop seasons

Cover crops are grown between cash crop seasons to reduce erosion, add organic matter, and suppress weeds.

Question 29: Which plant hormone is the primary driver of fruit ripening and is produced as a gas?

Cytokinin
Gibberellin
Ethylene (Correct answer)
Auxin

Correct answer: Ethylene

Ethylene is the gaseous plant hormone responsible for accelerating fruit ripening, leaf abscission, and other senescence processes in harvested crops.

Question 30: Which crop is classified as a C3 plant?

Sugarcane
Sorghum
Wheat (Triticum aestivum) (Correct answer)
Corn (Zea mays)

Correct answer: Wheat (Triticum aestivum)

Wheat uses the C3 photosynthetic pathway, fixing CO₂ directly via RuBisCO without a prior carbon-concentration step.

Question 31: Which photosynthetic adaptation allows cacti and pineapples to open their stomata at night to fix CO2?

C3 photosynthesis
Photorespiration
C4 photosynthesis
CAM photosynthesis (Correct answer)

Correct answer: CAM photosynthesis

Crassulacean Acid Metabolism (CAM) allows desert plants to open stomata at night, storing CO2 as malic acid, then using it for photosynthesis during the day with stomata closed to minimize water loss.

Question 32: Which nutrient is most commonly applied as starter fertilizer placed near the seed at planting?

Phosphorus (Correct answer)
Sulfur
Calcium
Potassium

Correct answer: Phosphorus

Phosphorus starter fertilizer placed near the seed promotes early root development and seedling vigor, especially in cold soils.

Question 33: Soil organic matter improves soil structure primarily by doing what?

Increasing bulk density
Reducing microbial activity
Raising soil pH
Promoting aggregate formation (Correct answer)

Correct answer: Promoting aggregate formation

Organic matter binds soil particles into aggregates, improving aeration, water infiltration, and tilth.

Question 34: Which group of insects are important biological control agents for aphids in crops?

Thrips and spider mites
Cutworms and armyworms
Ladybugs (lady beetles) and parasitic wasps (Correct answer)
Wireworms and white grubs

Correct answer: Ladybugs (lady beetles) and parasitic wasps

Lady beetles and parasitic wasps are natural enemies of aphids, feeding on or parasitizing them and reducing aphid population growth.

Question 35: In agronomy, what is meant by 'yield potential' of a crop variety?

The yield expected after accounting for typical pest losses
The minimum yield required for the crop to be economically viable
The maximum yield achievable under ideal growing conditions with no limiting factors (Correct answer)
The average yield achieved on a typical farm

Correct answer: The maximum yield achievable under ideal growing conditions with no limiting factors

Yield potential is the theoretical maximum output a crop variety can produce when grown without resource limitations such as water, nutrients, or pests.

Question 36: Center pivot irrigation systems are designed to apply water in what pattern?

Uniform grid using overhead sprinklers
Linear strips along field contours
Rectangular grid
Circular pattern around a central pivot point (Correct answer)

Correct answer: Circular pattern around a central pivot point

Center pivots rotate around a fixed central point, applying water in a circular pattern and covering large areas efficiently.

Question 37: Which crop disease is caused by Fusarium graminearum and affects the heads of wheat and barley?

Powdery mildew
Septoria leaf blotch
Crown rust
Fusarium head blight (scab) (Correct answer)

Correct answer: Fusarium head blight (scab)

Fusarium head blight (scab), caused by Fusarium graminearum, infects wheat and barley heads, causing yield loss and contaminating grain with mycotoxins like DON.

Question 38: What crop of the following exhibits protandry?

Chili
Tomato
Carrot (Correct answer)
Brinjal

Correct answer: Carrot

Protandry is a condition where the male reproductive organs (anthers) mature and shed pollen before the female reproductive organs (stigmas) become receptive. This mechanism promotes cross-pollination and prevents self-pollination within the same flower. Among the given options, carrot (Daucus carota) flowers are known to exhibit protandry, where the anthers release pollen before the stigmas are ready to receive it.

Question 39: What is the period of plant development from germination to the initiation of flowering called?

Vegetative phase (Correct answer)
Senescence phase
Dormancy phase
Reproductive phase

Correct answer: Vegetative phase

The vegetative phase spans from germination to floral initiation, during which the plant builds its root system, stems, and leaf canopy to accumulate resources for reproduction.

Question 40: What is the water potential of pure water at standard conditions?

-1 MPa
+1 MPa
0 MPa (Correct answer)
0.5 MPa

Correct answer: 0 MPa

Pure water has a water potential of 0 MPa by definition; adding solutes lowers water potential below zero, driving water movement into cells via osmosis.

Question 41: What does the term 'photoperiodism' refer to in plants?

A plant's response to the relative length of day and night (Correct answer)
The amount of light a plant absorbs
The rate of photosynthesis per day
The angle at which leaves capture sunlight

Correct answer: A plant's response to the relative length of day and night

Photoperiodism is a plant's physiological response to the duration of light and dark periods, which often triggers flowering.

Question 42: Which of the following crops produces non-edible oil cakes?

Mustard
Soybean
Groundnut
Linseed (Correct answer)

Correct answer: Linseed

Oil cakes are the solid residues remaining after oil extraction from oilseeds. Linseed (flaxseed) oil cake contains compounds that make it unsuitable for direct human consumption and is primarily used as animal feed or fertilizer. In contrast, mustard, soybean, and groundnut oil cakes are generally edible and widely consumed by humans or used as high-protein animal feed.

Question 43: Which pest is the primary vector for Barley Yellow Dwarf Virus (BYDV) in small grains?

Armyworm
Wheat stem sawfly
Aphids (Correct answer)
Hessian fly

Correct answer: Aphids

Aphids, particularly the bird cherry-oat aphid and English grain aphid, transmit BYDV to wheat, barley, and oats during feeding.

Question 44: What term describes the transport of photosynthates (sugars) through the phloem from leaves to roots or fruits?

Osmosis
Translocation (Correct answer)
Cohesion-tension
Transpiration

Correct answer: Translocation

Translocation is the movement of sugars, amino acids, and other organic solutes through the phloem from source tissues (leaves) to sink tissues (roots, fruits, seeds) via pressure flow.

Question 45: What does the harvest index (HI) measure in crop production?

The efficiency of harvesting machinery
The weight of straw relative to grain weight
The number of plants harvested per hectare
The proportion of total biomass partitioned into the harvestable product (Correct answer)

Correct answer: The proportion of total biomass partitioned into the harvestable product

Harvest index is the ratio of economically harvestable yield (grain, fruit) to total above-ground dry biomass, indicating how efficiently a crop converts total growth into useful product.

Question 46: What is the benefit of narrow row spacing (15 inches vs. 30 inches) in soybean production?

Reduced seeding rate needed
Faster canopy closure and weed suppression (Correct answer)
Lower risk of disease
Easier equipment access

Correct answer: Faster canopy closure and weed suppression

Narrow rows allow soybean canopy to close faster, suppressing weeds and capturing more sunlight earlier in the season.

Question 47: What is herbicide resistance in weeds?

Inherited ability of a weed biotype to survive a herbicide dose that kills normal plants (Correct answer)
Temporary tolerance of weeds to low herbicide doses
Weed dormancy triggered by herbicide application
Herbicide breakdown before it reaches target weeds

Correct answer: Inherited ability of a weed biotype to survive a herbicide dose that kills normal plants

Herbicide resistance is a heritable trait in weed populations that allows surviving plants to tolerate doses that would kill susceptible biotypes of the same species.

Question 48: What does 'test weight' measure in grain marketing?

Weight per bushel volume (grain density) (Correct answer)
Moisture content of grain
Kernel size uniformity
Protein content percentage

Correct answer: Weight per bushel volume (grain density)

Test weight measures the weight of a bushel of grain (lbs/bu), indicating grain density, quality, and often end-use value.

Question 49: What is leaching requirement in irrigated agriculture?

Drainage coefficient for tile drainage design
Volume of water needed to reach field capacity
Additional irrigation water needed to flush excess salts below the root zone (Correct answer)
Amount of fertilizer needed per irrigation cycle

Correct answer: Additional irrigation water needed to flush excess salts below the root zone

Leaching requirement is the fraction of applied irrigation water that must pass through and below the root zone to prevent salt accumulation to damaging levels.

Question 50: Which macronutrient is primarily responsible for vegetative growth and green color in plants?

Potassium
Nitrogen (Correct answer)
Calcium
Phosphorus

Correct answer: Nitrogen

Nitrogen is a key component of chlorophyll and amino acids, driving vegetative growth and green coloration.

Question 51: Which mineral nutrient is essential for chlorophyll synthesis and is found at the center of the chlorophyll molecule?

Potassium
Calcium
Magnesium (Correct answer)
Iron

Correct answer: Magnesium

Magnesium is the central atom in the chlorophyll molecule's porphyrin ring; deficiency causes interveinal chlorosis because plants cannot synthesize adequate chlorophyll.

Question 52: Which of the following countries produces the most cane sugar?

Hawaii
Cuba (Correct answer)
India
Indonesia

Correct answer: Cuba

Cuba has historically been renowned as a major global producer of cane sugar, earning it the moniker 'sugar bowl of the world' for a significant period. Its fertile soil and favorable climate made it exceptionally well-suited for sugarcane cultivation, and sugar exports were a cornerstone of its economy for centuries. While other nations like Brazil and India now lead in current production, Cuba's historical prominence in cane sugar production is undeniable.

Question 53: What role do mycorrhizal fungi play in plant nutrition?

Decompose crop residues
Suppress soil pathogens
Extend root surface area for nutrient uptake (Correct answer)
Fix atmospheric nitrogen

Correct answer: Extend root surface area for nutrient uptake

Mycorrhizal fungi colonize plant roots and extend hyphae into the soil, greatly increasing the root's effective absorptive surface area.

Question 54: Which soil order is commonly found in the Corn Belt and is highly productive for agriculture?

Mollisol (Correct answer)
Aridisol
Oxisol
Spodosol

Correct answer: Mollisol

Mollisols have thick, dark, organic-rich A horizons and high natural fertility, making them ideal for corn and soybean production.

Question 55: Which photosynthetic pathway do corn (maize) and sugarcane use to efficiently fix carbon in hot climates?

C4 pathway (Correct answer)
C3 pathway
CAM pathway
C2 pathway

Correct answer: C4 pathway

Corn and sugarcane use the C4 pathway, which spatially concentrates CO2 in bundle sheath cells to minimize photorespiration and improve photosynthetic efficiency.

Question 56: Which type of fertilizer application places nutrients directly in the root zone near the seed at planting?

Starter fertilizer (in-furrow or 2×2) (Correct answer)
Broadcast application
Foliar application
Topdressing

Correct answer: Starter fertilizer (in-furrow or 2×2)

Starter fertilizer placed in-furrow or 2 inches beside and 2 inches below the seed supplies readily available nutrients to seedling roots in cool, wet conditions.

Question 57: The term 'harvest index' refers to:

Ratio of grain yield to total above-ground biomass (Correct answer)
Percentage moisture at harvest
Number of harvests per season
Days from planting to harvest

Correct answer: Ratio of grain yield to total above-ground biomass

Harvest index is the proportion of above-ground dry matter that is partitioned into the harvested product (e.g., grain).

Question 58: Which soil texture has the largest individual particle size?

Silt
Clay
Loam
Sand (Correct answer)

Correct answer: Sand

Sand particles are the largest, ranging from 0.05 to 2.0 mm in diameter.

Question 59: What is Integrated Pest Management (IPM)?

Using only chemical pesticides to control pests
Eliminating all insects from a field
A strategy combining biological, cultural, mechanical, and chemical controls to minimize economic damage (Correct answer)
Relying solely on resistant varieties

Correct answer: A strategy combining biological, cultural, mechanical, and chemical controls to minimize economic damage

IPM uses a combination of methods—biological, cultural, mechanical, and chemical—to manage pests economically while minimizing environmental impact.

Question 60: What does the term 'quantitative trait' mean in plant genetics?

A trait unaffected by the environment
A trait controlled by many genes showing continuous variation (Correct answer)
A trait controlled by a single dominant gene
A trait visible only in recessive plants

Correct answer: A trait controlled by many genes showing continuous variation

Quantitative traits like yield and plant height are controlled by many genes with small individual effects and show continuous variation in populations.

Question 61: What is the primary pigment responsible for capturing light energy during photosynthesis?

Phycocyanin
Carotenoid
Anthocyanin
Chlorophyll a (Correct answer)

Correct answer: Chlorophyll a

Chlorophyll a is the primary photosynthetic pigment that directly participates in the light reactions by absorbing and transferring light energy.

Question 62: Which of the following crops may be grown without irrigation?

Wheat
Millets (Correct answer)
Soyabean
Sugarcane

Correct answer: Millets

Millets, such as sorghum, pearl millet, and finger millet, are known for their resilience and ability to thrive in harsh, arid, and semi-arid conditions with minimal water. They are often referred to as 'rainfed crops' because they can be successfully grown relying solely on natural rainfall, making them ideal for regions with limited irrigation facilities. Other crops like wheat, soybean, and sugarcane typically require more consistent moisture or irrigation for optimal yields.

Question 63: Which of the following is an example of a C4 crop plant?

Rice
Corn (maize) (Correct answer)
Soybean
Wheat

Correct answer: Corn (maize)

Corn (maize) is a C4 plant, using a more efficient photosynthetic pathway that reduces photorespiration and performs well in hot, sunny conditions.

Question 64: What is the directional growth of a plant shoot toward a light source called?

Hydrotropism
Thigmotropism
Phototropism (Correct answer)
Gravitropism

Correct answer: Phototropism

Phototropism is the directional growth response toward (positive) or away from (negative) light, mediated by asymmetric auxin distribution that causes differential cell elongation.

Question 65: Which plant hormone promotes seed germination, stem elongation, and is applied commercially to increase grape berry size?

Abscisic acid
Cytokinin
Gibberellin (Correct answer)
Ethylene

Correct answer: Gibberellin

Gibberellins promote stem elongation, seed germination, and fruit set; commercial applications to grapes increase berry size and are used to produce seedless varieties.

Question 66: Which agronomic practice most directly increases water use efficiency in dryland farming?

Increasing plant population
Applying more nitrogen
Harvesting earlier
Fallow periods and residue management (Correct answer)

Correct answer: Fallow periods and residue management

Strategic fallow periods and leaving crop residue on the surface help capture and retain precipitation for the subsequent crop.

Question 67: What is the primary function of phosphorus in plant metabolism?

Protein structure
Energy transfer via ATP (Correct answer)
Cell wall rigidity
Chlorophyll synthesis

Correct answer: Energy transfer via ATP

Phosphorus is a key component of ATP (adenosine triphosphate), which drives energy transfer in virtually all metabolic processes.

Question 68: What is the term for plants that complete their life cycle in one growing season?

Annual (Correct answer)
Biennial
Perennial
Ephemeral

Correct answer: Annual

Annual plants germinate, grow, flower, set seed, and die all within a single growing season.

Question 69: Backcrossing in plant breeding is primarily used to do what?

Induce polyploidy
Create new inbred lines
Increase genetic diversity
Transfer a single trait into an elite variety while preserving its background (Correct answer)

Correct answer: Transfer a single trait into an elite variety while preserving its background

Backcrossing involves repeated crosses to the recurrent (elite) parent to recover its genome while retaining a desired trait from the donor parent.

Question 70: Which macronutrient is most commonly associated with promoting root development in crops?

Calcium (Ca)
Nitrogen (N)
Phosphorus (P) (Correct answer)
Potassium (K)

Correct answer: Phosphorus (P)

Phosphorus is essential for energy transfer and root development, often applied to encourage strong root systems.

Question 71: What is the primary environmental concern associated with excess nitrate leaching from agricultural soils?

Groundwater and surface water contamination causing hypoxia and health risks (Correct answer)
Depletion of soil organic matter
Reduced crop yields from nitrogen deficiency
Soil acidification

Correct answer: Groundwater and surface water contamination causing hypoxia and health risks

Nitrate leaches readily through soil into groundwater and streams, contaminating drinking water and contributing to aquatic hypoxia (dead zones) in water bodies.

Question 72: Which type of soil horizon is most important for plant root development and nutrient uptake?

O horizon
C horizon
B horizon
A horizon (Correct answer)

Correct answer: A horizon

The A horizon (topsoil) contains the most organic matter and nutrients and supports the most root activity.

Question 73: Which US federal act regulates the production and sale of certified seed to ensure variety purity?

Clean Air Act
Federal Seed Act
Plant Variety Protection Act (Correct answer)
Seed Germination Standards Act

Correct answer: Plant Variety Protection Act

The Plant Variety Protection Act provides intellectual property protection for new, distinct, uniform, and stable plant varieties and encourages plant breeding.

Question 74: What is the purpose of a soil test before planting a cash crop?

Determine weed pressure
Predict weather patterns
Guide fertilizer and lime recommendations (Correct answer)
Select harvest equipment

Correct answer: Guide fertilizer and lime recommendations

Soil testing identifies nutrient levels and pH so farmers can apply the correct type and rate of fertilizer and lime for optimal crop production.

Question 75: What is CRISPR-Cas9 used for in modern plant breeding?

Producing double haploid lines by anther culture
Precise editing of specific DNA sequences in plant genomes (Correct answer)
Grafting scion tissue onto rootstock
Mapping chromosome locations using dye staining

Correct answer: Precise editing of specific DNA sequences in plant genomes

CRISPR-Cas9 is a gene-editing tool that allows breeders to make precise, targeted changes to specific locations in a plant's DNA.

Question 76: What does the term 'action threshold' mean in IPM decision-making?

The minimum pesticide rate on the label
The pest level at which management action should be taken to prevent economic damage (Correct answer)
The maximum pest density tolerated under any conditions
The number of pesticide applications allowed per season

Correct answer: The pest level at which management action should be taken to prevent economic damage

The action threshold is the pest population level that triggers a management response before economic damage occurs, allowing time for effective intervention.

Question 77: Which process converts ammonium (NH4+) to nitrate (NO3-) in the soil?

Immobilization
Nitrification (Correct answer)
Denitrification
Mineralization

Correct answer: Nitrification

Nitrification is a two-step microbial process that oxidizes ammonium to nitrite and then to nitrate.

Question 78: In corn production, what is the 'critical period for weed control'?

After tasseling when grain fill begins
At planting when seed germination occurs
2–4 weeks after planting when soil is warming
V1 to V8 growth stages when weeds compete most for resources (Correct answer)

Correct answer: V1 to V8 growth stages when weeds compete most for resources

Weeds emerging with corn during the V1–V8 period cause the greatest yield loss because they compete directly for light, water, and nutrients during early crop establishment.

Question 79: What is 'combining ability' in hybrid crop breeding?

A measure of how well inbred lines perform in hybrid combinations (Correct answer)
The ability of a plant to self-pollinate
The rate at which a crop accumulates dry matter
The capacity of a variety to grow in multiple climates

Correct answer: A measure of how well inbred lines perform in hybrid combinations

Combining ability refers to how well an inbred line performs when crossed with other lines, with GCA being average performance and SCA being specific cross performance.

Question 80: Which cultural practice is most effective at slowing the development of herbicide-resistant weed populations?

Increasing herbicide application rates
Using the same herbicide product every year
Applying herbicides only in problem areas
Rotating herbicide modes of action and integrating non-chemical weed control (Correct answer)

Correct answer: Rotating herbicide modes of action and integrating non-chemical weed control

Rotating herbicide modes of action and adding cultural and mechanical controls prevents any single resistance mechanism from becoming dominant in a weed population.

Question 81: What is the purpose of a testcross in plant breeding evaluation?

To detect chromosome abnormalities
To confirm a plant is diploid
To evaluate the general combining ability of inbred lines using a common tester (Correct answer)
To measure germination rate under stress

Correct answer: To evaluate the general combining ability of inbred lines using a common tester

Testcrossing inbred lines to a common tester allows breeders to assess their combining ability and predict hybrid performance.

Question 82: What is the purpose of a riparian buffer strip adjacent to farm fields?

Supply irrigation water to adjacent fields
Create habitat for pest insects
Provide additional crop production area
Filter runoff, trap sediment and nutrients, and protect waterways (Correct answer)

Correct answer: Filter runoff, trap sediment and nutrients, and protect waterways

Riparian buffers are strips of vegetation along waterways that intercept surface runoff, trap eroded sediment and nutrients, and protect stream health.

Question 83: What is the microbial process that converts organic nitrogen in soil organic matter into plant-available ammonium (NH4+)?

Nitrogen fixation
Denitrification
Ammonification (Correct answer)
Nitrification

Correct answer: Ammonification

Ammonification (mineralization) is the decomposition of organic nitrogen compounds (proteins, nucleic acids) into ammonium by soil bacteria and fungi, making nitrogen available for plant uptake.

Question 84: The C4 photosynthetic pathway is advantageous over C3 in which condition?

Cool, moist climates
High temperature and high light intensity (Correct answer)
Low light intensity
Shaded environments

Correct answer: High temperature and high light intensity

C4 plants like corn and sorghum use a carbon-concentrating mechanism that reduces photorespiration under hot, high-light conditions.

Question 85: Which soil textural class has the highest water-holding capacity?

Sand
Gravel
Clay (Correct answer)
Loam

Correct answer: Clay

Clay soils have small particles with large surface areas, giving them the greatest water-holding capacity.

Question 86: What is the beneficial insect Trichogramma used for in integrated pest management?

Pollinating crops
Parasitizing the eggs of lepidopteran pest insects (Correct answer)
Decomposing crop residues
Controlling soil-dwelling nematodes

Correct answer: Parasitizing the eggs of lepidopteran pest insects

Trichogramma wasps are minute parasitic insects that lay their eggs inside the eggs of moth and butterfly pests, killing them before they hatch.

Question 87: What is the Leaf Area Index (LAI)?

The ratio of total one-sided leaf area to ground surface area (Correct answer)
The ratio of root surface area to leaf area
A measure of average leaf thickness in a canopy
The number of leaves per plant

Correct answer: The ratio of total one-sided leaf area to ground surface area

LAI is the total one-sided leaf area per unit of ground area; it quantifies canopy light interception capacity and is closely related to crop productivity potential.

Question 88: Which gas is fixed by nitrogen-fixing bacteria in legume root nodules?

Methane (CH₄)
Atmospheric nitrogen (N₂) (Correct answer)
Oxygen (O₂)
Carbon dioxide (CO₂)

Correct answer: Atmospheric nitrogen (N₂)

Rhizobium bacteria in legume root nodules convert atmospheric nitrogen gas (N₂) into ammonium, a form plants can use.

Question 89: Which irrigation method delivers water directly to the root zone and is the most water-efficient?

Center pivot irrigation
Flood irrigation
Drip (trickle) irrigation (Correct answer)
Furrow irrigation

Correct answer: Drip (trickle) irrigation

Drip irrigation delivers water slowly and directly to the plant root zone through emitters, minimizing evaporation and runoff losses.

Question 90: Which measure describes the volume of water stored in a soil profile available to plants?

Available water capacity (AWC) (Correct answer)
Bulk density
Infiltration rate
Saturated hydraulic conductivity

Correct answer: Available water capacity (AWC)

Available water capacity is the difference between field capacity and permanent wilting point, representing the water plants can extract from the soil profile.

Question 91: What is the primary benefit of subsurface tile drainage in humid regions?

Prevents leaching of applied nutrients
Reduces crop yield by lowering water table
Increases irrigation water efficiency
Removes excess water from root zone, allowing earlier field operations and better aeration (Correct answer)

Correct answer: Removes excess water from root zone, allowing earlier field operations and better aeration

Tile drainage removes excess soil water, improving soil aeration for root growth, allowing earlier spring field access, and reducing denitrification losses.

Question 92: What is the primary goal of marker-assisted selection (MAS) in plant breeding?

To cross distantly related species
To identify phenotypically superior plants by eye
To use DNA markers linked to traits for faster, more accurate selection (Correct answer)
To eliminate the need for field trials

Correct answer: To use DNA markers linked to traits for faster, more accurate selection

MAS uses molecular markers associated with desired traits to select superior plants without waiting for phenotypic expression, speeding up breeding cycles.

Question 93: What is an 'economic threshold' in pest management?

The pest density at which control action must be taken to prevent economic loss (Correct answer)
The cost of applying a single pesticide application
The number of pests that can be controlled per dollar spent
The maximum legal pesticide residue level

Correct answer: The pest density at which control action must be taken to prevent economic loss

The economic threshold is the pest population level at which the cost of crop damage equals the cost of control, triggering a management decision.

Question 94: Which soil texture class has the highest water-holding capacity?

Sandy loam
Coarse sand
Silt loam
Clay (Correct answer)

Correct answer: Clay

Clay soils have the highest water-holding capacity due to their small particle size and large surface area.

Question 95: Which of the following crops can withstand draught better?

Pigeon pea
Cowpea (Correct answer)
Green gram
Blackgram

Correct answer: Cowpea

Cowpea (Vigna unguiculata) is renowned for its exceptional drought tolerance compared to many other pulse crops. It possesses a deep root system that allows it to access water from deeper soil layers and has physiological mechanisms to cope with water stress. This makes it a crucial crop for cultivation in arid and semi-arid regions where water availability is limited and rainfall is erratic.

Question 96: The cation exchange capacity (CEC) of a soil indicates its ability to do what?

Fix atmospheric nitrogen
Drain excess water
Hold and supply nutrients (Correct answer)
Resist compaction

Correct answer: Hold and supply nutrients

CEC measures the soil's capacity to hold positively charged nutrient ions and supply them to plants.

Question 97: Potassium deficiency in crops typically first appears as what symptom?

Stunted new growth
Marginal leaf scorch on older leaves (Correct answer)
Purple coloration of stems
Yellowing of young leaves

Correct answer: Marginal leaf scorch on older leaves

Potassium is mobile in plants, so deficiency symptoms—scorched leaf margins—appear first on older, lower leaves.

Question 98: What is deficit irrigation in water-limited agriculture?

Using reclaimed wastewater for irrigation
Applying more water than the crop needs to build soil water reserves
Irrigating only during crop establishment
Intentionally applying less than full ET replacement to maximize water productivity (Correct answer)

Correct answer: Intentionally applying less than full ET replacement to maximize water productivity

Deficit irrigation deliberately applies less than full crop ET replacement during less-sensitive growth stages to conserve water while accepting minor yield reductions.

Question 99: What is the primary carbon-fixing enzyme in C3 photosynthesis?

PEP carboxylase
Malate dehydrogenase
RuBisCO (Correct answer)
Pyruvate kinase

Correct answer: RuBisCO

RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes CO2 fixation in the Calvin Cycle and is the most abundant enzyme on Earth, though it can also bind O2, causing photorespiration.

Question 100: What is the most critical growth period for corn when water stress causes the greatest yield loss?

V6 to V10 vegetative stage
Silking through early grain fill (R1-R3) (Correct answer)
Grain dry-down period
Germination and emergence

Correct answer: Silking through early grain fill (R1-R3)

Water stress at silking and early grain fill (R1-R3) can cause poor pollination, kernel abortion, and the greatest proportional yield loss in corn.

Question 101: What is the net ATP yield per glucose molecule during complete aerobic cellular respiration?

20 ATP
2 ATP
36–38 ATP (Correct answer)
8 ATP

Correct answer: 36–38 ATP

Complete aerobic respiration of one glucose molecule yields approximately 36–38 ATP through glycolysis, the Krebs cycle, and oxidative phosphorylation via the electron transport chain.

Question 102: Soil organic matter contributes most directly to which soil property?

Improved soil structure and water retention (Correct answer)
Increased soil pH
Decreased nutrient availability
Reduced microbial activity

Correct answer: Improved soil structure and water retention

Soil organic matter improves aggregation, tilth, and water-holding capacity, making soils more productive and erosion-resistant.

Question 103: What is the primary role of nitrogen in plant growth?

Regulating water uptake
Strengthening cell walls
Building proteins and chlorophyll (Correct answer)
Facilitating seed germination

Correct answer: Building proteins and chlorophyll

Nitrogen is a key component of amino acids, proteins, and chlorophyll, making it essential for vegetative growth and photosynthesis.

Question 104: In integrated pest management (IPM), the 'economic threshold' is defined as:

Minimum yield loss acceptable to the grower
Maximum allowable pesticide cost per acre
Point at which all pests are eliminated
Pest density at which control action must be taken to prevent economic loss (Correct answer)

Correct answer: Pest density at which control action must be taken to prevent economic loss

The economic threshold is the pest population level at which the cost of management equals the economic damage caused, triggering a control decision.

Question 105: Which USDA zone of crop pest reporting helps agronomists track insect migration patterns?

Pest Management Strategic Plans (PMSP)
USDA Plant Hardiness Zone Map
National Pesticide Information Center (NPIC)
Cooperative Agricultural Pest Survey (CAPS) (Correct answer)

Correct answer: Cooperative Agricultural Pest Survey (CAPS)

The CAPS program coordinates state and federal surveys to detect and monitor invasive and emerging agricultural pest threats across the US.

Question 106: Which physiological process in plants is most directly affected by nitrogen deficiency?

Epicuticular wax deposition
Root hair formation
Seed coat hardening
Protein synthesis and chlorophyll production (Correct answer)

Correct answer: Protein synthesis and chlorophyll production

Nitrogen is a building block of amino acids, proteins, and chlorophyll, so its deficiency causes stunted growth and characteristic yellowing (chlorosis).

Question 107: Which management practice helps conserve soil moisture in dryland farming systems?

Frequent tillage to break surface crust
Planting crops earlier in spring
Applying gypsum to soil surface
Leaving crop residue on the soil surface and minimizing tillage (Correct answer)

Correct answer: Leaving crop residue on the soil surface and minimizing tillage

Crop residue mulch on the surface shades the soil, reduces evaporation, and improves water infiltration in dryland systems where stored moisture is critical.

Question 108: The concept of 'evapotranspiration' (ET) in agronomy combines which two processes?

Nutrient uptake and leaching
Photosynthesis and respiration
Soil evaporation and plant transpiration (Correct answer)
Infiltration and runoff

Correct answer: Soil evaporation and plant transpiration

Evapotranspiration is the combined water loss from soil surface evaporation and plant leaf transpiration, used to schedule irrigation.

Question 109: Soil salinity is measured using which instrument or method?

Refractometer
Tensiometer
Electrical conductivity meter (Correct answer)
Penetrometer

Correct answer: Electrical conductivity meter

Electrical conductivity (EC) meters measure the concentration of dissolved salts in a soil-water solution.

Question 110: What is the primary greenhouse gas emitted from flooded rice paddies?

Nitrous oxide (N2O)
Ammonia (NH3)
Methane (CH4) (Correct answer)
Carbon dioxide (CO2)

Correct answer: Methane (CH4)

Flooded rice paddies create anaerobic conditions that promote methanogenesis by archaea, making rice production a significant source of methane emissions.

Question 111: What is the primary reason that waterhemp is so difficult to control in corn and soybean production?

It only germinates in fall
It grows only in wet soils
It has an extremely long germination window, is dioecious, and has evolved resistance to many herbicide classes (Correct answer)
It cannot be controlled by any herbicide

Correct answer: It has an extremely long germination window, is dioecious, and has evolved resistance to many herbicide classes

Waterhemp's extended germination period, separate male and female plants (dioecious), high seed production, and multi-site herbicide resistance make it extremely difficult to manage.

Question 112: Which cover crop is most commonly used to add nitrogen back to the soil?

Hairy vetch (Correct answer)
Winter rye
Oats
Buckwheat

Correct answer: Hairy vetch

Hairy vetch is a legume that fixes atmospheric nitrogen through root nodule bacteria, making it a popular nitrogen-building cover crop.

Question 113: What is vernalization in crop production?

Application of fertilizers in early spring
A period of cold temperature exposure required to induce flowering (Correct answer)
The process of seed germination under warm temperatures
Treatment of seeds with hormones to break dormancy

Correct answer: A period of cold temperature exposure required to induce flowering

Vernalization is the process by which prolonged exposure to cold temperatures promotes flowering in certain crops, such as winter wheat, allowing them to flower in spring.

Question 114: What is the cation exchange capacity (CEC) of soil a measure of?

Soil's ability to hold positively charged nutrient ions (Correct answer)
Soil's ability to retain anions
Soil organic matter percentage
Rate of water infiltration

Correct answer: Soil's ability to hold positively charged nutrient ions

CEC measures how many positively charged cations (like Ca²⁺, Mg²⁺, K⁺) a soil can hold and exchange with plant roots.

Question 115: The law of the minimum, attributed to Justus von Liebig, states that:

Nutrients interact synergistically to maximize yield
Excessive nutrients are as harmful as deficiencies
Growth is limited by the nutrient present in the least relative amount (Correct answer)
Crop yield increases proportionally with each added nutrient

Correct answer: Growth is limited by the nutrient present in the least relative amount

Liebig's Law of the Minimum states that plant growth is constrained by the single most limiting nutrient, regardless of other nutrient levels.

Question 116: What is nitrogen use efficiency (NUE) in crop production?

The ratio of grain protein to total nitrogen in the plant
The proportion of applied nitrogen that is taken up and used by the crop (Correct answer)
The amount of nitrogen fixed by legumes
Total nitrogen applied per acre per year

Correct answer: The proportion of applied nitrogen that is taken up and used by the crop

NUE measures what fraction of the nitrogen applied as fertilizer is actually taken up and utilized by the crop, with typical values around 50% for corn.

Question 117: The process by which atmospheric nitrogen is converted into ammonia by microorganisms is called:

Nitrification
Biological nitrogen fixation (Correct answer)
Ammonification
Denitrification

Correct answer: Biological nitrogen fixation

Biological nitrogen fixation is performed by microorganisms like Rhizobium that convert N₂ gas into ammonia (NH₃).

Question 118: Which of the following is an illustration of an intercrop?

Rice
Bajra
Linseed
Moong (Correct answer)

Correct answer: Moong

Intercropping is the practice of growing two or more crops simultaneously on the same field. Moong (green gram) is a common legume frequently intercropped with cereals like bajra (pearl millet) or maize. Legumes like moong are beneficial intercrops because they fix atmospheric nitrogen, enriching the soil and benefiting the companion crop.

Question 119: Which practice is most effective at reducing soil erosion on sloped farmland?

Deep tillage
Monoculture
Fall plowing
Contour farming (Correct answer)

Correct answer: Contour farming

Contour farming involves planting across slopes to slow water runoff and reduce soil erosion on hillsides.

Question 120: Which soybean growth stage is most critical for final yield determination?

R3 (beginning pod)
V3 (vegetative)
R1 (flowering)
R5 (beginning seed fill) (Correct answer)

Correct answer: R5 (beginning seed fill)

The R5 stage (beginning seed fill) is most critical because seed size and number are being determined, directly setting final yield.

Question 121: What is 'heterosis' (hybrid vigor) in plant breeding?

Genetic uniformity in a population
Resistance to cross-pollination
Reduced yield in hybrid offspring
Superior performance of F1 hybrids over parental averages (Correct answer)

Correct answer: Superior performance of F1 hybrids over parental averages

Heterosis refers to the superior performance of F1 hybrid offspring compared to the average of their parent inbred lines.

Question 122: Liming a soil primarily corrects which soil problem?

High salinity
Poor drainage
Low phosphorus levels
Excessive acidity (Correct answer)

Correct answer: Excessive acidity

Agricultural lime (calcium carbonate) neutralizes soil acidity by reacting with hydrogen ions to raise pH.

Question 123: Which of the following is considered a legume cover crop used to improve soil nitrogen?

Hairy vetch (Correct answer)
Oats
Buckwheat
Winter rye

Correct answer: Hairy vetch

Hairy vetch (Vicia villosa) is a legume cover crop that fixes atmospheric nitrogen through its symbiotic relationship with Rhizobium bacteria.

Question 124: What is the primary advantage of using certified seed over saved farm seed?

Guaranteed genetic purity, germination rate, and freedom from weed seeds (Correct answer)
Longer shelf life
Higher moisture content
Lower cost per bag

Correct answer: Guaranteed genetic purity, germination rate, and freedom from weed seeds

Certified seed is tested and guaranteed to meet standards for genetic purity, germination percentage, and freedom from noxious weed seeds.

Question 125: The harvest index (HI) of a crop is defined as what?

Ratio of grain yield to total above-ground biomass (Correct answer)
Total biomass per acre
Number of harvestable seeds per plant
Moisture content at harvest

Correct answer: Ratio of grain yield to total above-ground biomass

Harvest index is the proportion of total above-ground dry matter that is in the economically valuable grain portion.

Question 126: What is evapotranspiration (ET) used for in irrigation management?

Predicting frost dates
Measuring rainfall totals
Estimating crop water use to schedule irrigation timing and amounts (Correct answer)
Calculating herbicide dilution rates

Correct answer: Estimating crop water use to schedule irrigation timing and amounts

ET estimates the combined water loss from soil evaporation and plant transpiration, providing the basis for scheduling irrigation to replace crop water use.

Question 127: The process by which plants lose water vapor through small pores in their leaves is called:

Transpiration (Correct answer)
Respiration
Evaporation
Osmosis

Correct answer: Transpiration

Transpiration is the process by which water moves through a plant and evaporates from aerial parts, primarily through stomata.

Question 128: Which type of irrigation delivers water directly to the root zone with minimal evaporation loss?

Sprinkler irrigation
Drip irrigation (Correct answer)
Flood irrigation
Furrow irrigation

Correct answer: Drip irrigation

Drip irrigation delivers water slowly and directly to the root zone through emitters, greatly reducing evaporation and water waste.

Question 129: Which tillage practice leaves the greatest amount of crop residue on the soil surface?

Chisel plowing
Moldboard plowing
Disk tillage
No-till (Correct answer)

Correct answer: No-till

No-till farming leaves essentially all crop residue undisturbed on the surface, maximizing erosion protection and water retention.

Question 130: Which practice is a core principle of regenerative agriculture that builds soil organic carbon?

Applying high rates of synthetic nitrogen fertilizer
Keeping soils covered and minimizing disturbance with cover crops and reduced tillage (Correct answer)
Frequent deep tillage to aerate soils
Eliminating all crop rotations

Correct answer: Keeping soils covered and minimizing disturbance with cover crops and reduced tillage

Keeping soils covered with living roots or residue and minimizing tillage disturbance builds soil organic carbon and improves soil biological health.

Question 131: Which weed management practice uses crop competition to suppress weed growth?

Hand weeding
Fallowing
Post-emergence herbicide application
Increasing crop seeding rate and narrow row spacing (Correct answer)

Correct answer: Increasing crop seeding rate and narrow row spacing

Increasing seeding rate and using narrow rows promote faster crop canopy closure, shading weeds and limiting their access to light and resources.

Question 132: Which trait in Bt corn was introduced through genetic engineering?

Nitrogen fixation
Herbicide resistance to glyphosate
Drought tolerance
Insect resistance via Bacillus thuringiensis toxin (Correct answer)

Correct answer: Insect resistance via Bacillus thuringiensis toxin

Bt corn contains a gene from the soil bacterium Bacillus thuringiensis that produces proteins toxic to specific insect pests like European corn borer.

Question 133: What is the primary purpose of crop rotation in agronomic systems?

Break pest and disease cycles (Correct answer)
Reduce irrigation needs
Increase soil temperature
Increase soil pH

Correct answer: Break pest and disease cycles

Crop rotation disrupts the life cycles of pests, pathogens, and weeds that are host-specific to a single crop.

Question 134: What is the doubled haploid (DH) technique used for in corn breeding?

Producing tetraploid corn lines
Rapidly producing homozygous inbred lines in one to two seasons (Correct answer)
Inducing flowering in short-day plants
Creating sterile hybrid seed

Correct answer: Rapidly producing homozygous inbred lines in one to two seasons

The DH technique colchicine-doubles haploid plants derived from pollen or unfertilized eggs to create fully homozygous inbred lines in just one or two generations.

Question 135: Which fertilizer source has the highest nitrogen content by weight?

Ammonium sulfate (21-0-0)
Anhydrous ammonia (82-0-0) (Correct answer)
Urea (46-0-0)
Ammonium nitrate (34-0-0)

Correct answer: Anhydrous ammonia (82-0-0)

Anhydrous ammonia contains approximately 82% nitrogen by weight, the highest of any commercially used nitrogen fertilizer.

Question 136: What is the Ogallala Aquifer significant for in US agriculture?

It supplies drinking water to the eastern seaboard
It is a major underground water source for irrigation in the Great Plains states (Correct answer)
It is a freshwater source used for Pacific Northwest irrigation
It is the primary source of surface water for the Mississippi Delta

Correct answer: It is a major underground water source for irrigation in the Great Plains states

The Ogallala Aquifer underlies about 174,000 square miles across eight Great Plains states and supplies irrigation water for approximately 30% of US groundwater-irrigated cropland.

Question 137: What crop has the highest likelihood of genetic variation?

Groundnut
Sorghum
Maize (Correct answer)
Rice

Correct answer: Maize

Maize (corn) exhibits a high degree of genetic variation primarily because it is an open-pollinated, cross-pollinating crop. Its reproductive system, with separate male and female flowers on the same plant (monoecious), naturally encourages outcrossing. This constant mixing of genetic material from different parent plants leads to a wide range of genetic diversity within maize populations, making it highly amenable to breeding and selection.

Question 138: What soil pH range is generally considered optimal for most agronomic crops in the US?

8.0–9.0
7.5–8.5
4.5–5.5
6.0–7.0 (Correct answer)

Correct answer: 6.0–7.0

A pH of 6.0–7.0 supports nutrient availability and beneficial microbial activity for most crops.

Question 139: What is the permanent wilting point (PWP) of a soil?

The optimal irrigation frequency for sandy soils
The maximum root depth for most field crops
The soil water content below which plants cannot recover turgor (Correct answer)
The soil water content at which irrigation must begin

Correct answer: The soil water content below which plants cannot recover turgor

The permanent wilting point is the soil moisture level at which plants can no longer extract water and will not recover even when water is added.

Question 140: Which of the following best describes 'vernalization' in crop plants?

The process of seed coat scarification
A method of weed control using cover crops
Exposure to cold temperatures required to trigger flowering (Correct answer)
The application of green manure to the soil

Correct answer: Exposure to cold temperatures required to trigger flowering

Vernalization is the induction of flowering by exposure to prolonged cold, a requirement for many winter cereals like winter wheat.

Question 141: What is the primary function of xylem tissue in crop plants?

Storage of starch reserves
Transport of sugars from leaves to roots
Gas exchange in leaves
Transport of water and minerals from roots to shoots (Correct answer)

Correct answer: Transport of water and minerals from roots to shoots

Xylem is the vascular tissue that conducts water and dissolved minerals upward from the roots to the rest of the plant through lignified, hollow dead cells.

Question 142: What does the Calvin Cycle (light-independent reactions) primarily produce?

NADPH
Glyceraldehyde-3-phosphate (G3P) (Correct answer)
ATP
Oxygen

Correct answer: Glyceraldehyde-3-phosphate (G3P)

The Calvin Cycle uses ATP and NADPH from the light reactions to fix CO2 into glyceraldehyde-3-phosphate (G3P), which serves as the building block for glucose.

Question 143: What is the primary role of potassium (K) in plant physiology?

Nucleic acid synthesis
Enzyme activation and stomatal regulation (Correct answer)
Component of chlorophyll molecule
Structural component of proteins

Correct answer: Enzyme activation and stomatal regulation

Potassium activates over 60 enzymes and is essential for guard cell function, which controls stomatal opening and water use efficiency.

Question 144: What is the recommended corn plant population for most US Corn Belt fields (plants per acre)?

50,000–60,000
20,000–25,000
10,000–15,000
32,000–36,000 (Correct answer)

Correct answer: 32,000–36,000

Most Corn Belt hybrids are planted at 32,000–36,000 seeds per acre to balance yield potential and resource use.

Question 145: Which of the following is a common method for measuring soil moisture in irrigated fields?

Refractometer
Tensiometer (Correct answer)
Lysimeter
Penetrometer

Correct answer: Tensiometer

Tensiometers measure soil water tension (suction), which indicates how tightly water is held in the soil and when irrigation is needed.

Question 146: Roundup Ready crops were engineered to be tolerant to which herbicide?

Metolachlor
Glyphosate (Correct answer)
Atrazine
2,4-D

Correct answer: Glyphosate

Roundup Ready crops contain a modified EPSPS gene that confers tolerance to glyphosate (Roundup), allowing herbicide application over the top of crops.

Question 147: Which corn growth stage is characterized by the silks emerging from the ear?

R1 (Correct answer)
V6
R3
VT

Correct answer: R1

R1 is the silking stage in corn, when silks emerge from the husks and are ready for pollination.

Question 148: The corn rootworm beetle's economic damage to corn is primarily caused by what?

Beetle feeding on pollen and silks
Adult beetles defoliating leaves
Adults boring into stalks
Larval feeding on roots, reducing water and nutrient uptake and causing lodging (Correct answer)

Correct answer: Larval feeding on roots, reducing water and nutrient uptake and causing lodging

Corn rootworm larvae feed on corn roots, reducing the plant's ability to uptake water and nutrients and causing yield loss and lodging.

Question 149: Waterlogged soils reduce crop yields primarily by causing what condition?

Frost damage to shallow roots
Oxygen depletion in the root zone, causing anaerobic conditions harmful to roots (Correct answer)
Excessive salt accumulation
Excess nitrogen leaching only

Correct answer: Oxygen depletion in the root zone, causing anaerobic conditions harmful to roots

Waterlogged soils are saturated with water, displacing oxygen and creating anaerobic conditions that impair root respiration, nutrient uptake, and plant growth.

Question 150: Which nutrient deficiency causes interveinal chlorosis in young leaves?

Nitrogen
Iron (Correct answer)
Phosphorus
Potassium

Correct answer: Iron

Iron deficiency causes interveinal chlorosis in young (newest) leaves because iron is immobile in the plant.

Question 151: What is the primary purpose of crop rotation in agronomy?

Improve farm equipment longevity
Reduce labor costs
Break pest and disease cycles while maintaining soil fertility (Correct answer)
Increase irrigation efficiency

Correct answer: Break pest and disease cycles while maintaining soil fertility

Crop rotation disrupts pest and disease cycles and helps maintain soil nutrient balance by alternating crops with different nutrient needs.

Question 152: The R1 growth stage in soybeans corresponds to what developmental event?

Pod fill initiation
Seed maturation
Emergence of first trifoliate leaf
Beginning of flowering (Correct answer)

Correct answer: Beginning of flowering

R1 in soybeans marks the beginning of flowering, when the first open flower appears at any node on the main stem.

Certified Crop Adviser (CCA) International Exam

The Certified Crop Adviser (CCA) International Exam certifies professionals in crop advisory services across four core agronomy competency areas: Soil and Water Management, Nutrient Management, Crop Management, and Pest Management.

150

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150 min

Time Limit

70%

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