Agricultural Engineering: Machinery, Duty, Delta and Irrigation Efficiency
Tillage and sowing machinery
Primary tillage uses the mouldboard or disc plough; secondary tillage the harrow, cultivator or rotavator; sowing uses the seed drill, dibbler or transplanter, followed by threshers and winnowers. Match implement width and draft to the power source, and remember that a rotavator can prepare seedbed tilth in a single pass.
Irrigation fundamentals
- Delta is the depth of water (cm) applied over the crop season; duty is the area (ha) irrigated per cumec of flow - the two move in opposite directions.
- 1 ha-cm = 100 m³ = 1,00,000 litres.
- Application efficiency: surface flooding 40–60%, furrow 60–70%, sprinkler 70–80%, drip 85–95%.
- Gross depth = net depth ÷ application efficiency.
Worked example
A pump delivers 30 litres per second. To apply 5 cm to 1 ha: Volume = 10,000 m² × 0.05 m = 500 m³ = 5,00,000 litres. Time = 5,00,000 ÷ 30 = 16,667 s ≈ 4.6 hours. At 70% application efficiency the gross requirement becomes 5 ÷ 0.7 ≈ 7.1 cm, so pumping time rises to about 6.6 hours.
Traps that cost marks
- Confusing delta (depth) with duty (area per unit flow).
- Ignoring application efficiency, which makes every irrigation estimate optimistic.
- Mixing horsepower and kilowatts (1 hp ≈ 0.746 kW).
- Forgetting that 1 hectare = 10,000 m² in volume conversions.