Soil and Water Conservation: Erosion Processes and Control Measures
This domain tests whether you can identify the process degrading a field, choose a suitable measure, and justify it from slope, rainfall and soil. Answers score when the measure is named precisely and matched to the erosion type.
Recognise the process
- Raindrop splash detaches soil particles and seals the surface.
- Sheet erosion removes a thin, uniform layer and is easily missed.
- Rill erosion cuts small channels that close with ordinary tillage.
- Gully erosion cuts channels too deep to cross with a plough; it needs structural treatment.
- Wind erosion lifts the finest particles and dominates dry, bare, sandy tracts.
Match the measure
- Agronomic: contour farming, strip cropping, mulching, cover crops, crop rotation, conservation tillage.
- Mechanical: contour bunds, graded bunds, bench terraces, check dams, grassed waterways, percolation tanks.
- Wind control: shelterbelts, windbreaks, stubble mulching.
Contour bunds hold water on gentle slopes where moisture is the limiting factor; graded bunds carry excess runoff safely to a waterway on steeper or higher-rainfall land. Bench terraces suit steep hill slopes where cultivation must be continued.
Worked example
A field has an 8% slope. Using the vertical interval rule VI = (S/2) + 2, with S in per cent and VI in feet: VI = (8/2) + 2 = 6 ft. Horizontal interval HI = 100 x VI / S = 100 x 6 / 8 = 75 ft. Reasoning: bunds must be spaced closer as the slope steepens so that runoff is intercepted before it gains velocity; HI is always longer than VI because it is measured along the ground surface.
Traps that cost marks
- Reporting HI when the question asks for VI.
- Prescribing a gully plug for sheet erosion.
- Treating bunds as a replacement for vegetative cover; they work best together.
- Calling a grassed waterway a barrier when it is a drainage channel.