Agriculture and Plantation Engineering
Agriculture and Plantation Engineering in IESL Part I tests how engineering principles are applied to soil–water–plant systems, irrigation and drainage, erosion control, farm machinery, and plantation processing for crops such as tea, rubber, coconut and paddy.
Core rules and concepts
- Soil water storage: total available water TAW = (θFC − θPWP) × root-zone depth; readily available water RAW = MAD × TAW, where MAD is the management allowed depletion.
- Irrigation interval ≈ RAW / ETc, with ETc = Kc × ETo. ETo is the reference evapotranspiration; Kc is the crop coefficient.
- Gross application depth = net requirement / application efficiency. Effective rainfall reduces the net requirement.
- Erosion: the Universal Soil Loss Equation A = R·K·LS·C·P; contour drains, terraces and cover crops reduce LS and C.
- Machinery: drawbar power = draft × forward speed; tractive efficiency falls as wheel slip increases.
Worked example
A 600 mm root zone has field capacity 32% by volume and permanent wilting point 15% by volume. MAD is 50% and ETc is 5 mm/day. Then TAW = (0.32 − 0.15) × 600 = 102 mm; RAW = 0.50 × 102 = 51 mm; interval = 51 / 5 ≈ 10 days. With 70% application efficiency, gross depth = 51 / 0.70 ≈ 73 mm. The reasoning is to convert volumetric moisture to a depth, apply MAD to TAW, then divide by the daily crop demand before correcting for losses.
Traps that cost marks
- Using gravimetric moisture without bulk density to convert to a depth.
- Applying MAD to field capacity instead of to TAW.
- Mixing ETo with ETc, or ignoring effective rainfall and application losses.
- Forgetting that heavy machinery causes compaction, reducing infiltration and root penetration.