Q.97
Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Barber (1995) defined the bio-available nutrient as the "one that is present in a pool of ions in the soil and can
move to the plant root during plant growth if the root is close enough”
Reason (R) : Bray's (1954) concept of nutrient mobility suggests that anions like NO3’, Cl or HCO;" are classified as
“mobile” nutrients, while cations like K, Mg2 and Ca" are classified as “immobile” nutrients.
In light of the above statements, choose the correct answer from the options given below.
- Assertion (A) is True: In submerged paddy soils, the redox potential ($E_h$) drops rapidly from $+400\text{ to }+600\text{ mV}$ (aerobic) down to $-150\text{ to }-250\text{ mV}$ (strongly reduced).
- Reason (R) is True: Depletion of dissolved molecular oxygen by aerobic microorganisms forces facultative and obligate anaerobic bacteria to utilize alternative terminal electron acceptors ($ ext{NO}_3^-, ext{Mn}^{4+}, ext{Fe}^{3+}, ext{SO}_4^{2-}$).
- Relationship: Both statements are accurate soil biogeochemical facts, but Reason (R) describes sequential microbial reduction rather than the primary operational definition of redox potential.
- Conclusion: Both (A) and (R) are correct but (R) is NOT the correct explanation of (A) (Option 2).
Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
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