Soil Fertility and Plant Nutrition
Soil Fertility and Plant Nutrition - This domain tests essential nutrients, deficiency symptoms, manures and fertilizers, soil testing and fertilizer calculations.
Core rules
- Seventeen elements are essential: C, H, O, N, P, K, Ca, Mg, S (macronutrients) and Fe, Mn, Zn, Cu, B, Mo, Cl, Ni (micronutrients).
- Mobile nutrients (N, P, K, Mg) show deficiency first in older leaves; immobile nutrients (Ca, Fe, B) show it in young leaves.
- Organic sources: FYM, compost, green manure and vermicompost; legumes add nitrogen through Rhizobium.
- Fertilizer grades: urea 46-0-0, DAP 18-46-0, MOP 60% K2O, SSP 16% P2O5 plus sulphur and calcium.
- INM combines organic manure, chemical fertilizer and biofertilizer to maintain soil health.
Worked example
Recommended dose is 120 kg N/ha. Urea contains 46% N, so urea needed = 120 ÷ 0.46 = 260.9 kg/ha, about 261 kg. Reasoning: divide the nutrient dose by the fraction of nutrient in the product; never divide by the percentage number without converting it to a fraction. For 0.5 ha, use 130.5 kg urea.
Traps
- Do not treat P2O5 and K2O as elemental P and K.
- DAP supplies both N and P; counting only P2O5 over-applies nitrogen.
- Deficiency in young leaves is not nitrogen deficiency.
- Over-application can cause lodging, salinity and groundwater pollution.
- Soil testing measures available nutrients, not total nutrients.