ICAR AIEEA PG Agronomy 14 July 2023 (Shift 1) Paper

Wavelength boundaries of solar spectrum bands:

• Red light: $620-760\text{ nm}$ (absorbance peak for chlorophyll in Photosystem II and I) -> (IV).
• Blue light: $450-500\text{ nm}$ (strong chlorophyll and carotenoid absorbance band) -> (II).
• Ultraviolet radiation: $\lt 400\text{ nm}$ ($100-400\text{ nm}$) -> (I).
• Infrared radiation: $\gt 760\text{ nm}$ ($760-3000\text{ nm}$) -> (III).

NBPT pharmacology and kinetics:

• Assertion (A) is true: NBPT (N-(n-butyl) thiophosphoric triamide, sold under the trade name Agrotain) is the leading commercially utilized urease inhibitor coated onto urea to mitigate ammonia volatilization.
• Reason (R) is false: In soil environments, NBPT delays urea hydrolysis by competitively inhibiting urease for typically $7-14\text{ days}$ (up to a maximum of about $10-14\text{ days}$ depending on soil temperature and moisture), NOT for $25\text{ days}$. Hence, Assertion is true but Reason is false.

Physiological and geochemical facts regarding Silicon:

• Statement (A) is correct: Silicon is a recognized beneficial element accumulating in graminaceous crops like rice and sugarcane (silicon accumulator plants).
• Statement (B) is correct: Deposition of amorphous silica ($SiO_2\cdot nH_2O$) in epidermal cell walls creates a double silica-cellulose layer conferring mechanical rigidity and lodging resistance.
• Statement (C) is correct: Silicon alleviates metal toxicities and prevents zinc-deficiency-induced phosphorus toxicity by improving internal nutrient balance.
• Statement (D) is incorrect: Combined oxides of Si, Al, and Fe constitute approximately $90\%$ (not $60\%$) of the mineral fraction of Earth's crust and soil. Hence, (A), (B) and (C) only are correct.