Irrigation, Fertigation and Water Management
This domain tests water quality, drip scheduling, fertigation safety and drainage. The exam rewards calculations and practical prevention of emitter clogging and nutrient imbalance.
Core rules
- Use drip with 2–4 L/h emitters; filter water to 120–150 mesh and add a sand filter if source water is dirty.
- Check EC and pH of the feed solution; maintain pH around 5.5–6.5 for soilless crops and monitor root-zone EC.
- Schedule by crop demand and radiation, not by a fixed clock; a tensiometer or drainage fraction helps.
- Keep 15–30% drainage in cocopeat or rockwool to limit salt build-up.
- Never mix calcium nitrate with phosphate or sulphate fertilisers in the same stock tank; use separate A and B tanks.
Worked example
A tomato crop in cocopeat receives 1.5 L/plant/day, but drainage EC is 4.0 dS/m against a feed EC of 2.2. Reasoning: salts are accumulating, likely because drainage fraction is too low. Action: increase irrigation volume or frequency until drainage EC falls near feed EC, and check emitter uniformity. Do not simply raise feed EC.
Traps that cost marks
- Mixing calcium and phosphate stock solutions and blocking the drip line.
- Irrigating by fixed time while radiation and crop stage change.
- Ignoring water sodium and bicarbonate, which raise pH and affect nutrient uptake.
- Failing to flush lines and filters.