Nutrition and Irrigation
What this domain tests
Nutrition and Irrigation tests diagnosis and scheduling: essential nutrients, soil and tissue analysis, fertigation, evapotranspiration, regulated deficit irrigation and salinity. The exam expects calculations and correct sampling timing, not blanket fertiliser recommendations.
Nutrition principles
Nitrogen drives vigour and canopy growth; excess nitrogen reduces fruit quality and increases disease susceptibility. Potassium affects sugar accumulation, water regulation and fruit acidity. Phosphorus, calcium, magnesium and micronutrients such as iron, boron and zinc are needed in small amounts. Soil analysis guides long-term planning; leaf or petiole analysis guides seasonal correction. Sample at a defined phenological stage and from comparable leaves, usually opposite a cluster.
Irrigation scheduling
Crop evapotranspiration (ETc) = reference evapotranspiration (ETo) × crop coefficient (Kc). Irrigation replaces the deficit between ETc and effective rainfall. Regulated deficit irrigation (RDI) applies less water at chosen stages, often before veraison, to control vigour and berry size. Partial rootzone drying (PRD) alternates wet and dry sides of the rootzone. Salinity raises osmotic stress and can cause leaf burn; leaching may be needed where drainage allows.
Worked example
ETo is 6 mm/day and Kc is 0.7, so ETc = 4.2 mm/day. Since 1 mm over 1 ha equals 10 m³, ETc equals 42 m³/ha/day. If RDI is set at 80% of ETc, apply 33.6 m³/ha/day. With drip emitters of 2 L/h at 0.5 m spacing, each emitter delivers 48 L/day, so the run time must match the system’s application rate and distribution uniformity.
Traps that cost marks
Do not apply nitrogen to solve every weak-vine problem. Do not sample leaves after fertiliser application and assume the result represents the season. Do not confuse ETo with ETc. Do not impose RDI on young vines or during severe heat without checking vine stress.
Key points
- Soil analysis guides planning; tissue analysis guides correction.
- ETc = ETo × Kc.
- 1 mm of water over 1 ha equals 10 m³.
- RDI controls vigour but must be timed and monitored.
- Salinity affects water uptake and can require leaching.