Soil, Media, Compost and Nutrient Management
This domain tests the physical and chemical properties of nursery media, compost making and fertilizer calculations. Numerical questions usually ask you to convert a nutrient requirement into kilograms of a fertilizer.
Soil and media rules
- Most nursery crops grow best at pH 6.0–7.0; seedlings need low salinity, ideally EC below about 1.0 dS/m.
- A common soil-based mix is soil:sand:FYM at 1:1:1 or 2:1:1. A soilless mix may use cocopeat:perlite:vermicompost at about 3:1:1.
- Sterilize media by solarization, steam or approved chemicals; never use raw, fresh manure in propagation media.
- Compost with a C:N ratio near 25–30:1, keep it moist and turn it; mature compost is earthy, cool and free of original feedstock.
Nutrients and calculation
- Nitrogen supports leaf growth, phosphorus supports roots, potassium supports quality and stress tolerance. Deficiency symptoms include pale older leaves (N), purplish leaves (P), scorched margins (K) and interveinal yellowing (Fe).
- Fertilizer needed = nutrient required ÷ fractional analysis of the fertilizer.
Worked example
A batch of 2,000 plants needs 30 g N per plant, so total N = 2,000 × 30 g = 60,000 g = 60 kg N. Urea contains 46% N, so urea required = 60 ÷ 0.46 = 130.4 kg. If the recommendation also requires 20 kg P₂O₅, DAP (18-46-0) supplies 46% P₂O₅, so DAP = 20 ÷ 0.46 = 43.5 kg; that DAP also supplies 43.5 × 0.18 = 7.8 kg N, which must be subtracted from the urea calculation. The reasoning is that fertilizer grades are percentages, and combined fertilizers supply more than one nutrient.
Traps that cost marks
Treating urea as a phosphorus source; ignoring the N supplied by DAP; mixing lime with ammonium fertilizers; using raw manure; measuring pH of distilled water instead of a soil/water suspension.
Key points
- Fertilizer needed = nutrient required ÷ fractional analysis.
- DAP supplies both N and P₂O₅; subtract its N.
- Most nursery media target pH 6.0–7.0 and low EC.
- Compost C:N near 25–30:1 and mature before use.