Farm Machinery and Irrigation
Farm Machinery and Irrigation
This section covers irrigation water measurement, duty and delta, irrigation efficiencies, pumps and the matching of machinery and water application methods.
Core rules
- Duty is the area irrigated by a unit discharge, usually expressed in hectares per cumec.
- Delta is the total depth of water applied to a crop over its base period.
- The relation is delta (m) = 8.64 × base period (days) ÷ duty (ha/cumec).
- Conveyance losses occur in channels; application losses occur in the field. Drip irrigation generally has higher application efficiency than surface flooding.
- Centrifugal pumps suit low lifts; submersible pumps suit deep wells.
Worked example
A canal has a duty of 1,200 ha/cumec and a base period of 120 days. Delta = 8.64 × 120 ÷ 1,200 = 0.864 m, or 86.4 cm. The reasoning is to keep the base period in days and the duty in ha/cumec; the constant 8.64 converts the units to metres.
Mark-losing traps
- Reversing duty and delta in the formula.
- Using base period in months without converting to days.
- Assuming drip irrigation removes the need for scheduling; it improves efficiency but does not eliminate crop water demand.
- Quoting high application efficiency for unlevelled surface flooding.