Tillage, Seedbed Preparation and Soil Conservation
What the exam asks
Tillage, Seedbed Preparation and Soil Conservation tests tillage objectives, primary and secondary implements, conventional versus minimum and zero tillage, seedbed requirements and erosion-control measures. Numeric items may ask for soil volume or mass moved.
Core rules
- Primary tillage opens and loosens soil (mouldboard plough, disc plough); secondary tillage breaks clods and levels (harrow, cultivator, roller).
- A good seedbed is free of weeds, sufficiently fine, firm at sowing depth and loose above, with adequate moisture.
- Zero tillage avoids soil disturbance but still needs residue management, weed control and correct seeding; it is not simply abandoning ploughing.
- Water erosion includes sheet, rill and gully erosion; wind erosion is serious on loose, dry, bare soil. Conservation measures include contour bunding, terracing, grass waterways, mulching and residue retention.
- Excessive tillage increases organic-matter loss, compaction and erosion; minimum tillage saves fuel and time but needs suitable machinery.
Worked example
A field is ploughed to 15 cm depth. One hectare is 10,000 m2, so the tilled volume is 10,000 × 0.15 = 1,500 m3. With bulk density 1.4 t m−3, soil mass moved = 1,500 × 1.4 = 2,100 t. Reasoning: convert depth to metres, multiply by area, then by bulk density. This shows why repeated deep ploughing is costly and erosive.
Traps
A disc plough is primary, not secondary; a cultivator is usually secondary. Zero tillage does not mean zero residue or zero weeds. Contour bunds run across the slope, not down it. Do not confuse soil texture with tilth: tilth is the physical condition for sowing, not particle-size composition.