Agricultural Engineering and Farm Machinery
Agricultural Engineering and Farm Machinery tests the quantitative side of mechanisation and irrigation: power, work rate, moisture and water balance, always with units kept consistent.
Core rules
- Drawbar power (kW) = draft force (kN) × speed (m/s). Implement width and speed set work rate.
- Theoretical field capacity (ha/h) = (width in m × speed in km/h) ÷ 10. Effective capacity = theoretical × field efficiency (turning, loading, overlap).
- Irrigation efficiencies: surface 50–60 %, sprinkler 70–80 %, drip 85–95 %. Irrigation interval = (FC − PWP) × root-zone depth × allowable depletion ÷ ETc.
- Machinery matching: the tractor must have enough drawbar power, and the implement width must fit the available time window.
- Calibrate seed drills and sprayers by measuring output over a known distance, not by trusting the label setting.
Worked example
A 3 m implement at 6 km/h: theoretical capacity = (3 × 6) ÷ 10 = 1.8 ha/h. At 80 % field efficiency, effective capacity = 1.44 ha/h. A 10 ha field needs 10 ÷ 1.44 = 6.9 h of actual work. If only 6 h per day are available and the job must finish in a day, 3 m is too narrow; a 4 m unit gives (4 × 6) ÷ 10 × 0.8 = 1.92 ha/h and finishes in 5.2 h.
Traps that cost marks
Mixing km/h with m/s in power calculations; scheduling with theoretical instead of effective capacity; quoting sprinkler efficiency for a drip system; assuming a lighter tractor at higher speed is cheaper - slip and fuel per hectare often rise.