Manures and Fertilizer Management
Expect two kinds of question: classification of manures and fertilizers, and simple fertilizer-dose arithmetic converting a recommendation in kg/ha of N, P2O5 and K2O into bags of urea, SSP and MOP.
Core rules
- Bulky organic manures: FYM (about 0.5 per cent N), compost, vermicompost, green manure (dhaincha, sunhemp), oil cakes, bone meal. They supply organic carbon and improve soil physical properties.
- Biofertilizers: Rhizobium for legumes, Azotobacter for non-legumes, Azospirillum for cereals, phosphate-solubilising bacteria, and mycorrhiza for phosphorus uptake.
- Straight fertilizers contain one nutrient: urea (46-0-0), SSP (0-16-0, also about 11 per cent sulphur and 19 per cent calcium), MOP (0-0-60), SOP (0-0-50). Complex fertilizers contain two or more: DAP (18-46-0), 19:19:19, 10:26:26, 20:20:0.
- Methods: broadcasting, band placement, placement near the root zone, fertigation through drip, foliar spray. Nitrogen is split-applied because it leaches and volatilises; phosphorus is placed below the seed because it moves little in soil.
- INM combines organic manure, biofertilizer and chemical fertilizer to sustain yield and soil health.
Worked example
A recommendation is 120:60:40 kg N:P2O5:K2O per hectare. How much urea, SSP and MOP is needed? Reasoning: urea = 120 ÷ 0.46 = 261 kg/ha; SSP = 60 ÷ 0.16 = 375 kg/ha (this also supplies about 41 kg sulphur); MOP = 40 ÷ 0.60 ≈ 67 kg/ha. Split the urea into a basal dose and top dressings; apply SSP and MOP basally.
Traps that cost marks
- Treating 60 kg P2O5 as 60 kg phosphorus (elemental P = P2O5 × 0.44).
- Dividing by the wrong percentage, or using DAP as the nitrogen source at the full dose.
- Applying all nitrogen at sowing.
- Assuming farmyard manure can replace fertilizer on an equal-nutrient basis.