Stem-nodulating green manure legumes:
Sesbania rostrata is an exceptional flood-tolerant, fast-growing African leguminous shrub that forms nitrogen-fixing symbiotic nodules on both its roots and aerial stems (stem nodules formed with Azorhizobium caulinodans).
This allows S. rostrata to continue fixing atmospheric nitrogen even when completely submerged under flooded paddy conditions, accumulating up to 150-200 kg N/ha in 45-55 days.
Sesbania aculeata (Dhaincha) and Crotalaria juncea (Sunnhemp) form nodules only on roots.

Plant nutrient deficiency symptoms:
Phosphorus (P) is a mobile nutrient; deficiency symptoms first appear on older (lower) leaves.
P deficiency impairs normal sugar metabolism and promotes abnormal accumulation of anthocyanin pigments, giving older leaves and stems a characteristic dark green followed by purplish, reddish, or bronzy-purple coloration.
Nitrogen deficiency causes uniform chlorosis (yellowing) of older leaves.
Potassium deficiency causes marginal scorching and necrosis of older leaf tips and edges.
Calcium deficiency appears on terminal buds and young growing points.

Characteristics of Black Soils (Vertisols / Regur):
(A) is true: They possess a characteristic deep dark grey to black colour (due to titaniferous magnetite and clay-humus complexes).
(B) is true: They have very high clay content (typically 40% to 60%, dominated by expanding 2:1 montmorillonite clay mineral).
(C) is false: Due to montmorillonite clay, they possess very high Cation Exchange Capacity (CEC) (30 to 60+ cmol(p+)/kg), NOT low CEC.
(D) is false: Indian black soils are notoriously poor/deficient in organic matter, nitrogen, and available phosphorus.
(E) is true: Known as 'Black Cotton Soils', they possess excellent moisture retention, making them ideally suited for rainfed cotton cultivation.