Irrigation, Water Management and Agricultural Engineering
Irrigation, Water Management and Agricultural Engineering tests the quantitative side of water: how much the crop needs, how much to apply, how efficiently it is applied, and what the salinity consequence is. Cyprus's scarcity and often saline boreholes make this a scoring opportunity for candidates who can compute.
Crop water requirement
Reference evapotranspiration (ET0) is computed by FAO-56 Penman–Monteith from weather data. ETc = ET0 × Kc, with Kc depending on crop and growth stage (initial, mid-season, late). Effective rainfall (Pe) reduces the requirement: irrigation requirement = ETc − Pe. Net irrigation requirement (NIR) is what the crop uses; gross (GIR) = NIR / application efficiency (drip 0.85–0.90, sprinkler 0.70–0.80, surface 0.50–0.60).
Scheduling and distribution
Drip suits saline water and tree crops because it wets a limited volume and keeps foliage dry. Uniformity is expressed as distribution uniformity (DU) or Christiansen uniformity (CU); low DU forces over-irrigation to satisfy the driest part. Soil moisture is monitored with tensiometers or capacitance probes.
Salinity
Leaching requirement LR = ECw / (5ECe − ECw), using irrigation water EC and the crop's threshold ECe. Drainage must exist or salts accumulate.
Worked example - drip block
Tomato; ET0 6 mm/day, Kc 1.1; drip efficiency 0.90; area 10 ha. ETc = 6 × 1.1 = 6.6 mm/day. GIR = 6.6 / 0.90 = 7.33 mm/day = 73.3 m³/ha/day. For 10 ha: 733 m³/day. Drip: 5,000 emitters/ha at 2 L/h = 10 m³/h/ha. Operating hours = 73.3 / 10 = 7.3 h/day. Reasoning: each step changes units; keep everything in mm (= L/m²) and convert at the end.
Traps
- Multiplying by efficiency when moving from NIR to GIR (wrong direction).
- Using the wrong Kc stage.
- Forgetting the wetted fraction under drip.
- Designing a schedule without checking pump capacity and filtration.
- Applying a leaching fraction without drainage.