Soil Science and Soil Fertility Management
Soil Science and Soil Fertility Management tests your grip on soil physical and chemical properties and on converting a fertilizer recommendation into bags of actual fertilizer.
Soil properties
- Texture (sand, silt, clay) governs water holding and aeration; structure governs porosity and root penetration.
- Chemical tests report pH, electrical conductivity, organic carbon, available N, P and K.
- Rajasthan's western sandy soils are low in organic matter and nitrogen, medium in phosphorus, usually high in potassium, and often calcareous or saline-alkaline; canal areas of Sri Ganganagar face secondary salinity.
Essential nutrients
Seventeen elements are essential. Primary: N, P, K. Secondary: Ca, Mg, S. Micro: Fe, Mn, Zn, Cu, B, Mo, Cl. Liebig's law of the minimum says growth is limited by the nutrient in shortest supply.
Worked example
Recommended dose 120 : 60 : 40 kg/ha of N : P₂O₅ : K₂O for wheat. Fertilizers: DAP (18% N, 46% P₂O₅), urea (46% N), MOP (60% K₂O). K: 40 ÷ 0.60 = 66.7 kg MOP. P: 60 ÷ 0.46 = 130.4 kg DAP, which also supplies 130.4 × 0.18 = 23.5 kg N. Remaining N = 120 − 23.5 = 96.5 kg → urea = 96.5 ÷ 0.46 = 209.8 kg. Apply all P, K and half the N at sowing; the rest at crown-root initiation.
Traps that cost marks
Treating P₂O₅ as elemental P; forgetting the nitrogen credit from DAP; dividing by 100 instead of the nutrient fraction; ignoring the soil test report when it changes the dose.