Brown manuring is practiced mainly to:

Correct option is A

· Brown manuring = knocking down Sesbania (Sesbania aculeata) grown with direct-seeded rice using 2,4-D at 25 DAS.
· Provides weed suppression, surface mulch, improves soil organic matter, and retains moisture.
Why other options are wrong
· (b) Not nitrogen application by fertilizer—brown manuring uses Sesbania, not urea.
· (c) Moisture retention is a benefit, but not the main purpose.