Irrigation, Drainage and Nursery Water Management
This domain tests water quality, irrigation methods, scheduling and drainage. The exam expects you to match the method to the nursery stage and to calculate a simple water or running-time requirement.
Water quality and methods
- Irrigation water should be near pH 6.5–7.5, with low salinity (EC below about 0.75–1.0 dS/m) and low sodium; avoid water with high bicarbonate or sodium.
- Use a rose can for seed beds and delicate seedlings, sprinklers for bed-grown stock, drip for polybags and orchards, mist for cuttings and subirrigation where overhead wetting spreads disease.
- Irrigate in the morning; check the media before watering rather than following a fixed clock. Water requirement can be estimated as ET × area × crop factor, plus a leaching fraction of about 10–20%.
- Drainage: shape beds with a 1–2% slope, provide peripheral drains, raise beds in heavy soils, and place a gravel layer or drainage hole in pots.
Worked example
A nursery has 1,000 polybags, each needing 500 mL per day. Daily requirement = 1,000 × 0.5 L = 500 L. If a drip system has 100 emitters rated at 4 L/h, output = 400 L/h, so running time = 500 ÷ 400 = 1.25 h. With 20% leaching, required water = 500 × 1.20 = 600 L, so running time = 600 ÷ 400 = 1.5 h. The reasoning is that leaching water is added to the crop requirement, not subtracted from it.
Traps that cost marks
Using overhead irrigation on disease-prone foliage; watering in the evening; assuming more water is always better; ignoring saline water; blocking drains with soil; forgetting that polybags need drainage holes.
Key points
- Water pH 6.5–7.5 and low EC are preferred.
- Match method to stage: rose can, sprinkler, drip, mist.
- Add 10–20% leaching water to the crop requirement.
- Beds need 1–2% slope and open drains.