Irrigation, Drainage & Pumping Systems

Agronomic soil conservation practices:
Assertion (A) is correct: Strip cropping is an agronomic practice in which erosion-permitting row crops (e.g., maize, sorghum) are grown in alternate strips across the slope with erosion-resisting close-growing crops (e.g., pulses, grasses, clovers).
Reason (R) is correct: Contour strip cropping combines contouring with vegetative filtering; dense vegetative strips slow runoff and trap detached sediment from the row strips, reducing soil loss to about half of that from simple contour farming alone.
However, Reason (R) compares relative effectiveness with contour farming; it does not explain the mechanical and agronomic arrangement defined in Assertion (A). Hence, (R) is NOT the explanation of (A).

Classification of tillage machinery:
Sub-surface tillage implements: Implements designed to cut roots, loosen soil, and kill weeds beneath the surface without turning or inverting the soil slice, leaving crop residue intact on the soil surface for moisture conservation and wind erosion control (stubble mulch farming):

• Sweeps (V-shaped sweeps)
• Straight subsurface blades / blade terracers
• Rod-weeders (revolving square rods operated 5 to 10 cm below surface).
  Lister (Middlebuster): A double-moldboard surface tillage/bedding implement used to make deep, open furrows and planting ridges on the surface. It inverts topsoil and creates distinct ridges, making it a surface bedding tool, NOT a subsurface conservation implement.

Hydraulics of water impounding behind contour bunds:
On a sloping land with slope

\(S\) (fraction), the horizontal distance between bunds \(\text{HI} = \frac{\text{VI}}{S}\). The volume of excess rainfall (\(R\)) falling on a 1-meter wide strip between consecutive bunds is: \[V_{\text{rain}} = \text{HI} \times 1 \times R = \frac{\text{VI}}{S} \times R\]

The impounded water behind the bund forms a triangular wedge of depth

\(h\) at the bund face and spreading uphill to a length \(L = \frac{h}{S}\). The storage volume of this triangular wedge per 1-meter width is: \[V_{\text{stored}} = \frac{1}{2} \times h \times L \times 1 = \frac{1}{2} \frac{h^2}{S}\]

Equating stored volume to excess rainfall volume:

\[\frac{1}{2} \frac{h^2}{S} = \frac{\text{VI}}{S} \times R \implies h^2 = 2 \cdot \text{VI} \cdot R\] \[h = \sqrt{2 \cdot \text{VI} \cdot R}\]

Given

\(\text{VI} = 2\text{ m} = 200\text{ cm}\) and \(R = 1\text{ cm}\): \[h = \sqrt{2 \times 200\text{ cm} \times 1\text{ cm}} = \sqrt{400} = 20\text{ cm}\]