ASRB NET: Agricultural Engineering

ASRB NET Agricultural Engineering covers farm machinery and power, irrigation and drainage, soil and water conservation and food process engineering. Questions often require formula-based estimates rather than descriptive recall.

Core concepts

• Implement draft depends on soil resistance, width, depth and speed; draft = specific resistance × width × depth.
• Field capacity: theoretical value in ha/h = width in m × speed in km/h divided by 10; actual field capacity is lower due to turns and overlap.
• Irrigation: application efficiency = water stored in the root zone divided by water delivered; distribution uniformity affects yield.
• Soil and water conservation: USLE is A = R K LS C P; each factor is multiplicative, so a misapplied factor changes the estimate.
• Food process engineering: drying curves, thermal death time and D or z values quantify preservation.

Worked example

A 1 ha field needs 60 mm net irrigation. If application efficiency is 60%, gross water required = 60 divided by 0.60 = 100 mm. Volume = 100 mm × 10,000 m² = 1,000 m³, because 1 mm over 1 ha equals 10 m³. Reasoning: net requirement is the water stored; gross must be larger to account for losses.

Traps that cost marks

• Reporting theoretical field capacity as achieved field capacity.
• Forgetting that 1 mm depth over 1 ha equals 10 m³.
• Using USLE with slope length in metres when the LS factor is tabulated for specific units.
• Treating pasteurisation as commercial sterilisation in process calculations.