Purple orange colour of older leaves is due to the deficiency of: | Agrigyan

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.

Rotational Intensity (RI) is calculated as:

\[\text{Rotational Intensity (\%)} = \frac{\text{Total Number of Crops in the Rotation}}{\text{Duration of Rotation (in years)}} \times 100\]

In the given cropping system:
Crops grown: Rice (Kharif) and Potato (Rabi) = 2 crops.
Fallow (Zaid) is not counted as a crop.
Total duration of this cropping cycle = 1 year.

\[\text{Rotational Intensity} = \frac{2}{1} \times 100 = 200\%\]

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.