PEC EPE Agricultural cheat sheet

Agricultural Engineering - Core Reference

• Tractor power take-off (PTO) standard speeds: 540 rpm at 540E economy setting and 1000 rpm; rated PTO power is measured at standard engine speed (often 540 rpm at 2200 rpm engine on older tractors).

• Drawbar power (kW) = draft force (kN) × forward speed (m/s). Draft of tillage implements rises roughly with speed squared for many soil-engaging tools, so doubling speed can more than double power demand.

• Tractor ballast rule: aim for a power-to-weight ratio near 25–35 kg/kW for field work; too light causes wheel slip, too heavy increases compaction and fuel use.

• Wheel slip target for field operations is typically 8–15% on firm soil; slip above ~20% wastes fuel and damages the surface. Slip (%) = (no-load travel − load travel) / no-load travel × 100.

• Sowing calibration: seed rate (kg/ha) = (seed collected per revolution × wheel revolutions per ha) / 1000; always check by turning the metering unit a set number of revolutions and weighing output.

• Sprayer calibration: application rate (L/ha) = (nozzle flow L/min × 600) / (boom spacing m × speed km/h). Nozzle flow varies with the square root of pressure, so doubling pressure raises flow about 41%.

• Irrigation: reference evapotranspiration (ET0) from Penman-Monteith or pan evaporation × pan coefficient; crop water use = ET0 × crop coefficient (Kc). Drip systems typically achieve 85–95% application efficiency versus 50–70% for furrow.

• Soil compaction risk: avoid field traffic when soil moisture is near field capacity; axle load above ~10 t/axle and tyre inflation pressure above ~100 kPa increase subsoil and topsoil damage respectively.

• Grain drying: moisture removal depends on air temperature, humidity, and airflow rate; safe long-term storage moisture is about 13–14% for wheat and maize and 12–13% for soybeans at ambient temperature.