Soil and Water Conservation Measures (Mechanical and Agronomic)
Mechanical and agronomic measures are tested together because the exam wants you to match a technique to a slope, soil and rainfall situation, and to know which measures are engineering works and which are crop-based.
Mechanical measures
- Contour bunding: earthen bunds along the contour (zero grade) on gentle slopes; they intercept runoff and let it infiltrate.
- Graded bunding: bunds carry a small longitudinal grade (about 0.2–0.5%) to lead surplus water to a safe outlet.
- Bench terracing: step-like levelled benches on steep land; also contour trenching, check dams, gully plugs, retaining walls and grassed waterways as safe disposals.
Agronomic measures
- Contour farming, strip cropping, cover cropping, crop rotation, mulching and conservation tillage.
- Vegetative barriers of vetiver (khus), Napier, subabul or agave reinforce bunds and slow runoff.
Worked example
A field has a 4% slope and the recommended vertical interval is 1.0 m. Horizontal interval = 100 × VI / slope% = 100 × 1.0/4 = 25 m. On a 200 m long slope, 200/25 = 8 strips fit, giving 7 internal bunds plus boundary bunds. Reasoning: VI is the height difference, HI the ground distance; the 100 converts percent slope to a ratio.
Traps
Confusing vertical interval with horizontal interval; specifying a grade for contour bunds (they are zero grade); classifying mulching as mechanical; forgetting a safe outlet so bunds breach.