1000 Most Important Agronomy MCQs with Explanation for ICAR JRF, NET, AFO & All Agriculture Exams
Which of the following soil textures is generally considered ideal for most agricultural crops? a) Sandy soil b) Clayey soil c) Loamy soil d) Silty soil
Answer: c) Loamy soil
Explanation: Loamy soil contains a balanced mixture of sand, silt, and clay particles (approximately 40% sand, 40% silt, and 20% clay). This texture provides good drainage, adequate water-holding capacity, proper aeration, and ease of tillage, making it ideal for most crops.*
The process of accumulation of salts in the soil surface layer is called: a) Leaching b) Salinization c) Calcification d) Podzolization
Answer: b) Salinization
Explanation: Salinization is the accumulation of soluble salts (primarily sodium, calcium, magnesium, potassium chlorides and sulfates) in the soil surface layer. This occurs mainly in arid and semi-arid regions due to high evaporation rates and improper irrigation practices.
Soil pH value 7.0 indicates: a) Acidic soil b) Alkaline soil c) Neutral soil d) Saline soil
Answer: c) Neutral soil
Explanation: Soil pH is measured on a scale of 0-14. pH values below 7 indicate acidic conditions, above 7 indicate alkaline conditions, and exactly 7.0 indicates neutral soil. Most crops grow best in slightly acidic to neutral soils (pH 6.0-7.0).*
Which of the following is NOT a method of soil conservation? a) Contour ploughing b) Strip cropping c) Shifting cultivation d) Terracing
Answer: c) Shifting cultivation
Explanation: Shifting cultivation (also called slash-and-burn agriculture) actually contributes to soil degradation and deforestation. Contour ploughing, strip cropping, and terracing are all effective soil conservation practices that help prevent erosion and maintain soil health.
The organic matter content of a typical agricultural soil should be ideally around: a) 0.5-1% b) 3-5% c) 10-15% d) 20-25%
Answer: b) 3-5%
Explanation: Ideal organic matter content for agricultural soils ranges from 3-5%. Organic matter improves soil structure, water-holding capacity, nutrient availability, and biological activity. Soils with less than 1% organic matter are considered degraded.*
Which horizon of soil profile is known as the topsoil or zone of maximum biological activity? a) O-horizon b) A-horizon c) B-horizon d) C-horizon
Answer: b) A-horizon
Explanation: The A-horizon (topsoil) is the surface mineral layer rich in organic matter and microorganisms. It’s where maximum biological activity occurs, including root growth, decomposition, and nutrient cycling. The O-horizon is organic layer above it.
Bulk density of an ideal agricultural soil should be: a) Less than 1.0 g/cc b) 1.2-1.4 g/cc c) 1.6-1.8 g/cc d) More than 2.0 g/cc
Answer: b) 1.2-1.4 g/cc
*Explanation: Ideal bulk density for plant growth ranges from 1.2-1.4 g/cc. Lower bulk density indicates good porosity and aeration, while higher bulk density (>1.6 g/cc) indicates compaction that restricts root growth and water movement.*
Black cotton soils are technically known as: a) Laterite soils b) Alluvial soils c) Regur soils d) Desert soils
Answer: c) Regur soils
Explanation: Black cotton soils are technically called Regur soils. They are rich in montmorillonite clay, which gives them high swelling and shrinking characteristics. These soils are found mainly in the Deccan plateau and are excellent for cotton cultivation.
The downward movement of water through soil is called: a) Capillary rise b) Percolation c) Evaporation d) Transpiration
Answer: b) Percolation
Explanation: Percolation is the downward movement of water through the soil profile under the force of gravity. This process is important for groundwater recharge and leaching of soluble salts and nutrients beyond the root zone.
Which nutrient deficiency causes whiptail disease in cauliflower? a) Nitrogen deficiency b) Phosphorus deficiency c) Molybdenum deficiency d) Zinc deficiency
Answer: c) Molybdenum deficiency
Explanation: Molybdenum deficiency causes whiptail disease in cauliflower and other cruciferous crops. The leaves become narrow, distorted, and develop a whip-like appearance. Molybdenum is essential for nitrogen metabolism in plants.
The water that is held tightly by soil particles and unavailable to plants is called: a) Capillary water b) Gravitational water c) Hygroscopic water d) Runaway water
Answer: c) Hygroscopic water
Explanation: Hygroscopic water is held so tightly by soil particles (at tensions greater than 31 atmospheres) that plants cannot extract it. Capillary water is available to plants, while gravitational water drains away quickly.
Which soil order covers the maximum area in India? a) Vertisols b) Aridisols c) Inceptisols d) Alfisols
Answer: c) Inceptisols
Explanation: Inceptisols cover the maximum area in India. These are moderately developed soils found in various climatic conditions. Alluvial soils, which are extensive in the Indo-Gangetic plains, fall under this order.
The process of breakdown of rocks and minerals into smaller particles by physical, chemical, and biological agents is called: a) Erosion b) Weathering c) Leaching d) Illuviation
Answer: b) Weathering
Explanation: Weathering is the disintegration and decomposition of rocks and minerals at or near the Earth’s surface through physical, chemical, and biological processes. This is the first step in soil formation.
Which of the following is a biological method of soil conservation? a) Gully plugging b) Contour bunding c) Mulching d) Rock dam construction
Answer: c) Mulching
Explanation: Mulching involves covering the soil surface with organic or inorganic materials to reduce evaporation, control erosion, and moderate soil temperature. It’s considered a biological/agronomic method. Gully plugging, contour bunding, and rock dams are mechanical measures.
Soil texture refers to: a) Arrangement of soil particles b) Relative proportion of soil separates c) Color of soil d) Organic matter content
Answer: b) Relative proportion of soil separates
Explanation: Soil texture refers to the relative proportions of sand, silt, and clay particles in the soil. Soil structure (option a) refers to the arrangement of these particles into aggregates.
The ideal C:N ratio for proper decomposition of organic matter in soil is: a) 10:1 b) 20:1 c) 30:1 d) 40:1
Answer: c) 30:1
Explanation: A C:N ratio of approximately 30:1 is ideal for microbial decomposition of organic matter. Wider ratios (e.g., 60:1) cause nitrogen immobilization, while narrower ratios (e.g., 10:1) lead to rapid decomposition and nitrogen release.
Which type of soil is most susceptible to wind erosion? a) Clayey soil b) Loamy soil c) Sandy soil d) Rocky soil
Answer: c) Sandy soil
Explanation: Sandy soils are most susceptible to wind erosion due to their low cohesion, large particle size, and lack of organic matter. They lack the binding agents that help hold soil particles together against wind forces.
The term “field capacity” refers to: a) Water held after free drainage has ceased b) Water available for plant growth c) Water held at permanent wilting point d) Total water holding capacity
Answer: a) Water held after free drainage has ceased
*Explanation: Field capacity is the amount of water held in the soil after excess gravitational water has drained away and the rate of downward movement has materially decreased, usually 2-3 days after rain or irrigation.*
Which micronutrient is essential for chlorophyll formation? a) Zinc b) Copper c) Iron d) Manganese
Answer: c) Iron
Explanation: Iron is essential for chlorophyll synthesis, though it’s not a component of the chlorophyll molecule. Iron deficiency causes interveinal chlorosis (yellowing between leaf veins) in young leaves.
Soil having pH less than 8.5, EC more than 4 dS/m, and ESP less than 15 is classified as: a) Saline soil b) Sodic soil c) Saline-alkali soil d) Acid soil
Answer: a) Saline soil
*Explanation: Saline soils (white alkali) have pH < 8.5, EC > 4 dS/m, and ESP < 15. Sodic soils (black alkali) have pH > 8.5, EC < 4 dS/m, and ESP > 15. Saline-alkali soils have properties of both.*
Which of the following crops is known as a soil-exhausting crop? a) Potato b) Sunhemp c) Cowpea d) Guar
Answer: a) Potato
Explanation: Potato is considered a soil-exhausting crop because it removes large quantities of nutrients from the soil, especially potassium. Sunhemp, cowpea, and guar are soil-improving crops as they fix atmospheric nitrogen and add organic matter.
Laterite soils are rich in: a) Iron and aluminum b) Calcium and magnesium c) Potassium and phosphorus d) Nitrogen and sulfur
Answer: a) Iron and aluminum
Explanation: Laterite soils are formed under tropical conditions with heavy rainfall and high temperature. They are rich in iron and aluminum oxides but poor in silica, calcium, magnesium, and organic matter. Their name comes from Latin “later” meaning brick.
The minimum organic carbon percentage required for a soil to be classified as “organic soil” is: a) 5% b) 10% c) 15% d) 20%
Answer: d) 20%
Explanation: For a soil to be classified as organic soil or histosol, it must contain at least 20% organic carbon (approximately 35% organic matter) if it’s never been drained, or 18% organic carbon if drained. Mineral soils have less organic matter.
Which practice helps in reducing soil erosion on sloping lands by cultivating along the contours? a) Contour farming b) Strip cropping c) Mulching d) Terracing
Answer: a) Contour farming
Explanation: Contour farming involves plowing, planting, and cultivating across the slope following the contour lines. This creates small ridges that act as barriers to water flow, reducing runoff and soil erosion on gentle to moderate slopes.
The wilting point of a plant occurs when soil moisture tension reaches approximately: a) 0.3 atmospheres b) 1 atmosphere c) 15 atmospheres d) 31 atmospheres
Answer: c) 15 atmospheres
Explanation: Permanent wilting point occurs when soil moisture tension reaches approximately 15 atmospheres (1.5 MPa). At this tension, plants cannot extract enough water from the soil to maintain turgor and will wilt permanently unless water is added.
A plant growing where it is not wanted is called a: a) Crop b) Weed c) Herb d) Shrub
Answer: b) Weed
Explanation: A weed is any plant growing where it is not desired. This definition is anthropocentric (human-centered) rather than botanical. The same plant species may be a crop in one context and a weed in another.
Which of the following is an example of a perennial weed? a) Chenopodium album (Bathua) b) Cyperus rotundus (Motha) c) Echinochloa crusgalli (Sawa) d) Trianthema portulacastrum (Sanatha)
Answer: b) Cyperus rotundus (Motha)
Explanation: Cyperus rotundus (nut grass or motha) is a perennial weed that reproduces through tubers, rhizomes, and seeds. It’s considered one of the world’s worst weeds due to its persistence and difficulty to control. The others are annual weeds.
The study of weeds and their management is called: a) Agronomy b) Weed science c) Horticulture d) Ecology
Answer: b) Weed science
Explanation: Weed science (or weed biology) is the branch of agricultural science that deals with the study of weeds, their characteristics, ecology, and methods of control. It encompasses both theoretical and practical aspects of weed management.
Which method of weed control is most effective against perennial weeds with underground propagules? a) Hand weeding b) Hoeing c) Summer ploughing d) Mulching
Answer: c) Summer ploughing
Explanation: Summer ploughing during hot months exposes underground weed propagules (rhizomes, tubers, bulbs) to high temperatures and desiccation, killing them. This is particularly effective for perennial weeds like Cyperus rotundus and Cynodon dactylon.
2,4-D is an example of: a) Contact herbicide b) Selective herbicide c) Non-selective herbicide d) Soil sterilant
Answer: b) Selective herbicide
*Explanation: 2,4-D (2,4-Dichlorophenoxyacetic acid) is a selective systemic herbicide that controls broadleaf weeds without harming monocot crops like wheat, maize, and rice. It mimics natural auxins, causing abnormal growth in susceptible plants.*
The critical period of crop-weed competition refers to: a) Entire crop growth period b) Initial growth stage c) Time when weeds cause maximum yield loss d) Time when weeds flower
Answer: c) Time when weeds cause maximum yield loss
*Explanation: The critical period of crop-weed competition is the specific time during crop growth when weeds must be controlled to prevent significant yield loss. For most crops, this is the first 30-45 days after sowing or transplanting.*
Which of the following is a parasitic weed? a) Cynodon dactylon (Doob) b) Striga asiatica (Witchweed) c) Echinochloa colona (Sawa) d) Cyperus iria
Answer: b) Striga asiatica (Witchweed)
Explanation: Striga (witchweed) is a parasitic weed that attaches to the roots of cereal crops like sorghum, maize, and millet, extracting water and nutrients. Other parasitic weeds include Orobanche (broomrape) and Cuscuta (dodder).
The process by which weeds release chemicals that inhibit the growth of neighboring plants is called: a) Parasitism b) Competition c) Allelopathy d) Symbiosis
Answer: c) Allelopathy
Explanation: Allelopathy is a biological phenomenon where plants release biochemicals (allelochemicals) that affect the growth, survival, or reproduction of other plants. Parthenium hysterophorus and Lantana camara are notorious allelopathic weeds.
Glyphosate is a: a) Selective herbicide b) Contact herbicide c) Non-selective systemic herbicide d) Pre-emergence herbicide
Answer: c) Non-selective systemic herbicide
Explanation: Glyphosate (Roundup) is a non-selective systemic herbicide that kills most plants it contacts. It inhibits the EPSPS enzyme, blocking amino acid synthesis. It’s translocated throughout the plant, making it effective against perennial weeds.
The weed flora of Rabi season includes: a) Echinochloa colonum b) Trianthema portulacastrum c) Chenopodium album d) Commelina benghalensis
Answer: c) Chenopodium album
Explanation: Chenopodium album (bathua or lamb’s quarters) is a major Rabi (winter) season weed. Echinochloa colonum, Trianthema portulacastrum, and Commelina benghalensis are typically Kharif (rainy) season weeds.
Which method of weed control involves covering the soil surface with black polythene? a) Solarization b) Mulching c) Hoeing d) Stale seedbed
Answer: b) Mulching (specifically plastic mulching)
Explanation: Plastic mulching (especially black polythene) covers the soil surface to suppress weed growth by blocking light and creating physical barrier. It also conserves moisture and moderates soil temperature. Solarization specifically uses transparent plastic to heat soil.
Atrazine is commonly used for weed control in: a) Wheat b) Rice c) Maize d) Pulses
Answer: c) Maize
Explanation: Atrazine is a selective herbicide widely used in maize (corn) cultivation for pre-emergence and early post-emergence control of broadleaf weeds and some grasses. It inhibits photosynthesis in susceptible plants.
The number of weed seeds present in the soil is called: a) Weed density b) Weed seed bank c) Weed frequency d) Weed biomass
Answer: b) Weed seed bank
Explanation: The weed seed bank is the natural storage of viable weed seeds in the soil. It can contain thousands of seeds per square meter and serves as the primary source for future weed infestations. Understanding it helps in planning long-term weed management.
Which of the following is an aquatic weed? a) Parthenium hysterophorus b) Eichhornia crassipes c) Lantana camara d) Xanthium strumarium
Answer: b) Eichhornia crassipes
Explanation: Eichhornia crassipes (water hyacinth) is a free-floating perennial aquatic weed native to South America. It’s considered one of the world’s worst aquatic weeds, causing problems in waterways, irrigation canals, and lakes through rapid growth.
The practice of creating conditions for weed seeds to germinate and then destroying them before sowing the crop is called: a) Stale seedbed technique b) Mulching c) Solarization d) Zero tillage
Answer: a) Stale seedbed technique
Explanation: Stale seedbed (or false seedbed) involves preparing the seedbed, allowing weeds to germinate, and then destroying them (through shallow tillage or herbicide) before sowing the crop. This reduces the initial weed pressure in the main crop.
Fluchloralin is a: a) Dinitroaniline herbicide b) Phenoxy herbicide c) Triazine herbicide d) Urea herbicide
Answer: a) Dinitroaniline herbicide
Explanation: Fluchloralin belongs to the dinitroaniline group of herbicides. These are pre-emergence, soil-applied herbicides that inhibit root development by affecting microtubule formation during cell division. Other examples include pendimethalin and trifluralin.
The weed that is also used as a medicinal plant and vegetable is: a) Amaranthus spinosus b) Parthenium hysterophorus c) Argemone mexicana d) Solanum nigrum
Answer: d) Solanum nigrum
Explanation: Solanum nigrum (black nightshade or makoi) is considered a weed but also has medicinal properties and its tender shoots and berries are used as vegetable in some regions. It contains solanine alkaloids and should be consumed when fully ripe.
The herbicide that kills weeds by contact action is: a) Glyphosate b) Paraquat c) 2,4-D d) Atrazine
Answer: b) Paraquat
Explanation: Paraquat is a contact herbicide that kills only the plant parts it touches. It’s non-selective and acts quickly by disrupting photosynthesis at the cellular level. Unlike systemic herbicides, it doesn’t translocate within the plant.
The term “SMART” in weed management stands for: a) Specific, Measurable, Achievable, Realistic, Time-bound b) Soil, Moisture, Air, Radiation, Temperature c) Strategic Management of Agricultural Resources and Technology d) Simple Mechanical And Rotational Techniques
Answer: a) Specific, Measurable, Achievable, Realistic, Time-bound
Explanation: In the context of Integrated Weed Management (IWM), SMART refers to setting Specific, Measurable, Achievable, Realistic, and Time-bound goals for weed control programs, borrowed from general management terminology.
Parthenium hysterophorus is also known as: a) Congress grass b) Nut grass c) Bermuda grass d) Barnyard grass
Answer: a) Congress grass
Explanation: Parthenium hysterophorus is commonly known as congress grass, carrot weed, or white top. It’s a serious weed native to Americas that causes health problems (allergies, dermatitis) in humans and animals, and reduces crop yields through allelopathy.
Which weed is known to cause photosensitization in animals when consumed? a) Cyperus rotundus b) Fagopyrum esculentum c) Hypericum perforatum d) Cuscuta reflexa
Answer: c) Hypericum perforatum
Explanation: Hypericum perforatum (St. John’s wort) contains hypericin, a photosensitizing compound that causes animals consuming it to become sensitive to sunlight, leading to skin inflammation, blistering, and other symptoms.
Pre-emergence herbicides are applied: a) Before sowing the crop b) After crop emergence c) After sowing but before crop and weed emergence d) At flowering stage
Answer: c) After sowing but before crop and weed emergence
Explanation: Pre-emergence herbicides are applied after sowing the crop but before the crop and weeds emerge from the soil. They control germinating weed seeds and seedlings. Examples include pendimethalin, atrazine (pre-emergence use), and oxyfluorfen.
The weed Cuscuta (dodder) is characterized by: a) Green leaves and photosynthesis b) Yellow thread-like stems without chlorophyll c) Aquatic habitat d) Grass-like appearance
Answer: b) Yellow thread-like stems without chlorophyll
Explanation: Cuscuta (dodder or amarbel) is a parasitic weed with yellow or orange thread-like stems that lack chlorophyll. It wraps around host plants and inserts haustoria into their vascular tissue to extract water and nutrients.
Integrated Weed Management (IWM) emphasizes: a) Complete reliance on herbicides b) Combining multiple weed control methods c) Only cultural methods d) Only biological control
Answer: b) Combining multiple weed control methods
Explanation: Integrated Weed Management (IWM) combines cultural, mechanical, biological, and chemical methods in a coordinated approach for sustainable weed control. It aims to reduce reliance on any single method, especially herbicides, to prevent resistance.
The first selective herbicide discovered was: a) Glyphosate b) 2,4-D c) Paraquat d) Atrazine
Answer: b) 2,4-D
*Explanation: 2,4-D (2,4-Dichlorophenoxyacetic acid) was discovered during World War II and commercialized in the late 1940s. It was the first selective herbicide, revolutionizing weed control in cereal crops by killing broadleaf weeds while leaving grasses unharmed.*
