1. In the context of nutrient use efficiency (NUE), which of the following factors most significantly contributes to the low NUE of urea in flooded rice systems due to denitrification losses?
a) High soil pH above 7.5
b) Anaerobic conditions and nitrate reductase activity
c) Volatilization of ammonia under alkaline conditions
d) Leaching losses in sandy soils
Correct Answer: b) Anaerobic conditions and nitrate reductase activity
In flooded rice, anaerobic microsites favor denitrification where nitrate (NO3-) is reduced to N2O and N2 gases by denitrifying bacteria, leading to 20-30% N loss; this is exacerbated by high organic matter and temperatures >25°C, unlike volatilization which occurs in surface-applied urea on calcareous soils.
2. The critical stage for irrigation in pearl millet under rainfed conditions in arid zones is from?
a) Germination to tillering
b) Panicle initiation to boot leaf stage
c) Flowering to grain filling
d) Seedling to jointing
Correct Answer: b) Panicle initiation to boot leaf stage
This 30-40 day period coincides with reproductive phase sensitivity to moisture stress, where water deficit reduces floret fertility by 50-70%; studies from CAZRI show yield drops >40% without supplemental irrigation here, unlike vegetative stages with higher resilience.
3. Which allelochemical primarily exuded by sorghum roots inhibits nitrification in associated legume intercrops, leading to enhanced N availability?
a) Sorghumone
b) Dhurrin
c) Hydroxybenzoxazinone
d) Sorgoleone
Correct Answer: d) Sorgoleone
Sorgoleone, a p-benzoquinone from root exudates, suppresses nitrifier bacteria (Nitrosomonas), reducing NO3- formation and favoring NH4+ retention, which legumes utilize efficiently; field trials indicate 15-20% higher NUE in sorghum-pigeonpea systems.
4. In the Liebig's Law of the Minimum, the 'minimum' nutrient for maize in alluvial soils of Indo-Gangetic plains is often?
a) Nitrogen
b) Phosphorus
c) Zinc
d) Iron
Correct Answer: c) Zinc
Zn deficiency limits maize yield despite adequate NPK due to impaired chlorophyll synthesis and enzyme activation (e.g., carbonic anhydrase); DTPA-extractable Zn <0.6 ppm correlates with 20-30% yield loss, as per AICRPAM data, overriding balanced fertilization effects.
5. The C4 photosynthetic pathway in crops like maize confers drought tolerance primarily through?
a) Higher RuBP carboxylase activity
b) Reduced photorespiration and higher CO2 fixation efficiency
c) Increased stomatal conductance
d) Enhanced water use efficiency via Kranz anatomy
Correct Answer: d) Enhanced water use efficiency via Kranz anatomy
Kranz anatomy separates mesophyll and bundle sheath cells, concentrating CO2 at Rubisco to minimize photorespiration (near zero vs. 25% in C3), achieving WUE of 50-60 kg/ha/mm vs. 20-30 in C3 crops under water stress.
6. Under subtropical conditions, the optimum nitrogen dose for hybrid rice (Oryza sativa) to maximize grain yield without lodging is?
a) 100-120 kg N/ha in three splits
b) 150-180 kg N/ha in two splits
c) 200-250 kg N/ha in four splits
d) 80-100 kg N/ha in one basal dose
Correct Answer: b) 150-180 kg N/ha in two splits
Hybrids require higher N for tillering and panicle exertion but split application (50% basal + 50% at tillering) prevents excessive vegetative growth and lodging; IRRI trials show 7-8 t/ha yield at this rate vs. 5-6 t/ha with unbalanced dosing.
7. The primary mechanism of herbicide resistance in Phalaris minor (littleseed canarygrass) to ACCase inhibitors like clodinafop is?
a) Target site mutation (Ala to Gly at 2078 locus)
b) Enhanced glutathione S-transferase activity
c) Reduced herbicide uptake
d) Increased cuticular wax deposition
Correct Answer: a) Target site mutation (Ala to Gly at 2078 locus)
Point mutation in the ACCase gene alters the enzyme binding site, conferring 10-100x resistance; molecular diagnostics confirm this in 70% resistant biotypes from Punjab wheat fields, unlike metabolic resistance via GST in other weeds.
8. In conservation agriculture, the 'residue retention' component reduces soil erosion by?
a) Increasing bulk density
b) Enhancing aggregate stability via mycorrhizal hyphae
c) Intercepting raindrop impact and reducing runoff velocity
d) Promoting earthworm activity only
Correct Answer: c) Intercepting raindrop impact and reducing runoff velocity
30% ground cover from residues dissipates kinetic energy of raindrops (reducing splash erosion by 90%) and slows surface flow (cutoff velocity from 0.5 to 0.2 m/s), as per USDA models; synergistic with no-till for 50-70% erosion control.
9. The Bray's P-1 method extracts phosphorus in acid soils, but in calcareous soils, which method is more accurate for available P estimation?
a) Olsen's sodium bicarbonate method
b) Mehlich-3
c) Lancaster method
d) Egner-Riehm method
Correct Answer: a) Olsen's sodium bicarbonate method
Olsen's (0.5 M NaHCO3, pH 8.5) targets Ca-P and Fe/Al-P fractions in high-pH (>7.5) soils, correlating better (r=0.85) with crop uptake than Bray's (acidic, underestimates in calcareous); critical limit 10-15 kg/ha P.
10. For sesame (Sesamum indicum) under rainfed vertisols, the critical period of weed competition is from?
a) 0-20 DAS
b) 20-40 DAS
c) 40-60 DAS
d) 60 DAS to harvest
Correct Answer: b) 20-40 DAS
This vegetative phase sees rapid crop growth but weeds like Echinochloa spp. compete for light/moisture, causing 30-50% yield loss if uncontrolled; beyond 40 DAS, sesame canopy closure suppresses weeds effectively.
11. The 'apparent nitrogen recovery' (ANR) in wheat is calculated as?
a) (N uptake in fertilized - N uptake in control) / N applied × 100
b) Total N uptake / N applied × 100
c) Grain N content / Total N applied × 100
d) N in residue / N applied × 100
Correct Answer: a) (N uptake in fertilized - N uptake in control) / N applied × 100
ANR measures agronomic efficiency, typically 40-60% in wheat; low values indicate losses via leaching/denitrification, guiding split applications for >70% recovery in loamy soils.
12. In dryland farming, the 'contingency crop planning' for delayed monsoon onset in black soils prioritizes?
a) Short-duration pearl millet (60-70 days)
b) Long-duration sorghum hybrids
c) Pulses like chickpea
d) Oilseeds like groundnut
Correct Answer: a) Short-duration pearl millet (60-70 days)
Varieties like HHB-67 escape terminal drought, yielding 1.5-2 t/ha vs. <1 t/ha for longer crops; sowing window shifts to mid-July, per CRIDA guidelines for rainfed Deccan plateau.
13. The micronutrient 'chlorine' deficiency in rice manifests as?
a) Bronzing of leaves and sterile pollen
b) White streaks on leaves
c) Mottled leaves and reduced tillering
d) Interveinal chlorosis
Correct Answer: a) Bronzing of leaves and sterile pollen
Cl- is essential for osmosis and photosynthesis; deficiency (<0.1% leaf Cl) in saline-leached soils causes 20-40% spikelet sterility, as seen in coastal Andhra Pradesh paddies.
14. Under precision agriculture, variable rate technology (VRT) for N application in potato uses?
a) Soil EC maps only
b) Canopy NDVI reflectance from drones
c) Uniform grid sampling
d) Weather-based models alone
Correct Answer: b) Canopy NDVI reflectance from drones
NDVI (0.7-0.9 threshold) detects N stress zones, enabling site-specific fertigation; trials show 15-25% N savings and 10% yield increase vs. uniform application.
15. The 'lysimeter' method measures crop evapotranspiration (ETc) by?
a) Weighing lysimeter pots daily for water loss
b) Penman-Monteith equation
c) Soil moisture depletion curves
d) Sap flow sensors in stems
Correct Answer: a) Weighing lysimeter pots daily for water loss
Gravimetric change in monoliths (1-2 m deep) gives precise ETc (e.g., 4-6 mm/day for wheat); FAO-56 uses it for Kc calibration, accounting for percolation/evaporation.
16. In weed science, the 'hyperaccumulation' trait in plants like Pteris vittata is exploited for?
a) Allelopathy enhancement
b) Phytoremediation of heavy metals
c) Bioherbicide production
d) Cover crop mulching
Correct Answer: b) Phytoremediation of heavy metals
Accumulates >1000 µg/g As in fronds, reducing soil bioavailability by 30-50%; transgenic approaches amplify this for Cd/Pb cleanup in contaminated agroecosystems.
17. For sugarcane ratoon cropping, the optimum trash management practice to enhance bud sprouting is?
a) Complete burning
b) Incorporation with 20 t/ha FYM
c) Surface retention only
d) Deep burial
Correct Answer: b) Incorporation with 20 t/ha FYM
Green trash mulching suppresses weeds/soil temp but incorporation recycles K (50-70 kg/ha) and microbes, boosting tillering by 25%; VSI studies show 15-20% ratoon yield gain.
18. The 'physiological maturity' in soybean is determined by?
a) 95% pod color change and maximum seed dry weight
b) Full flowering
c) Beginning seed fill
d) R8 stage only
Correct Answer: a) 95% pod color change and maximum seed dry weight
At R7-R8 (Fehr-Neilson scale), harvest index peaks (0.4-0.5); delaying harvest risks pod shatter (5-10% loss/day), optimizing oil/protein content.
19. In integrated nutrient management (INM), the synergistic effect of P and Zn application in basmati rice is due to?
a) Enhanced mycorrhizal colonization
b) Improved root exudation of phytosiderophores
c) Reduced P fixation in Fe oxides
d) Increased phosphatase activity
Correct Answer: b) Improved root exudation of phytosiderophores
Zn-P interaction boosts chelation of Fe/Mn, alleviating deficiencies; PAU trials report 10-15% yield uplift in Zn-deficient Tarai soils.
20. The 'ridge-furrow' planting system in cotton under rainfed conditions conserves soil moisture by?
a) 20-30% through reduced evaporation and runoff
b) Enhancing deep percolation
c) Increasing windbreaks
d) Promoting capillary rise only
Correct Answer: a) 20-30% through reduced evaporation and runoff
Ridges (30-45 cm) capture rainfall in furrows, delaying wilting point by 15-20 days; CICR data shows 1-1.5 t/ha extra lint yield in rain-shadow zones.
21. Critical phosphorus level for sorghum in red soils (Mehlich-3 extractable) is?
a) 5-10 ppm
b) 15-20 ppm
c) 25-30 ppm
d) >40 ppm
Correct Answer: b) 15-20 ppm
Below 15 ppm, P limits root proliferation and ATP synthesis, reducing yield by 20%; calibration curves from CRIDA indicate 40 kg P2O5/ha response.
22. The 'ammonification' process in soil organic matter decomposition is inhibited by?
a) High C:N ratio (>30:1)
b) Acidic pH <5.5
c) Aerobic conditions
d) Low temperature <10°C
Correct Answer: a) High C:N ratio (>30:1)
Immobilization dominates, tying up 20-30 kg N/ha; green manuring (C:N 15:1) accelerates release, per SOM dynamics models.
23. In aerobic rice systems, the water productivity (WP) improves by?
a) 50-100% over flooded systems due to reduced percolation
b) 20% via alternate wetting-drying
c) 10% with mulching only
d) No change
Correct Answer: a) 50-100% over flooded systems due to reduced percolation
Alternate wetting (5 cm)-drying cycles cut seepage (30-50% savings), achieving WP 1.0-1.5 kg grain/m³ vs. 0.5 in puddled; IRRI hybrids like PR 114 suited.
24. The resistance mechanism in Echinochloa colona to glyphosate is primarily?
a) EPSPS gene amplification (10-20 copies)
b) Reduced translocation
c) Target site mutation (Pro106Ser)
d) Enhanced vacuolar sequestration
Correct Answer: a) EPSPS gene amplification (10-20 copies)
Overexpression maintains shikimate pathway flux, conferring 5-50x resistance; qPCR confirms in Australian/Indian biotypes from direct-seeded rice.
25. For finger millet in hilly tracts, the sowing time to escape shoot fly (Atherigona soccata) is?
a) Early kharif (June first week)
b) Late kharif (August)
c) Rabi (November)
d) Zaid (March)
Correct Answer: a) Early kharif (June first week)
Seedling escape from oviposition peak (July); wrapped sowing with carbofuran reduces deadheart by 80%, per TNAU recommendations for >2 t/ha yield.
26. The 'nitrate reductase' activity in maize leaves peaks at?
a) Vegetative stage (V6)
b) Tasseling (VT)
c) Silking (R1)
d) Dough stage (R4)
Correct Answer: b) Tasseling (VT)
Correlates with max N demand for reproductive sinks; in vitro assay (1-2 µmol NO2-/g/h) guides sidedress N, preventing deficiency-induced yield loss (15-20%).
27. In saline sodic soils (pH >8.5, ESP >15%), the gypsum requirement (GR) is calculated as?
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Physical Science ICAR JRF 2020 Solved Question Paper pdf download Q. 1. Under what condition, denitrification is a major mechanism of nitrogen loss from the soil?1. Well-drained soil2. Fallow soils3.
