Manures and Fertilizers
What this domain tests
Organic manures, biofertilizers, fertilizer grades, straight and complex fertilizers, and the arithmetic of converting a recommended nutrient dose into bags of fertilizer.
Core rules
- Bulky organic manures: farmyard manure (about 0.5% N, 0.2% P2O5, 0.5% K2O), compost, vermicompost, green manures (dhaincha, sunhemp), oil cakes and poultry manure. They supply organic carbon and micronutrients besides nutrients.
- Biofertilizers: Rhizobium for legumes, Azotobacter and Azospirillum for non-legumes, phosphate-solubilising bacteria, and Azolla or blue-green algae for paddy.
- Straight fertilizers carry one nutrient: urea 46% N, single superphosphate 16% P2O5 plus about 11% sulphur, muriate of potash 60% K2O, ammonium sulphate 20.6% N. Complex fertilizers carry two or three: DAP 18-46-0, and NPK complexes such as 10-26-26 and 19-19-19.
- Fertilizer grade is always N–P2O5–K2O, never elemental P or K. Convert P2O5 to P by multiplying by 0.44 and K2O to K by 0.83.
- Placement: nitrogen in two or three splits, full phosphorus and potassium as a basal dose placed below and beside the seed, never in direct contact with germinating seed.
- Integrated nutrient management combines organics, biofertilizers and mineral fertilizer to protect soil health and raise efficiency.
Worked example
Recommended dose 120:60:60 kg N, P2O5, K2O per hectare. Reasoning: urea for N = 120 / 0.46 = 261 kg. Using DAP for phosphorus, DAP needed = 60 / 0.46 = 130 kg, which also supplies 130 × 0.18 = 23.5 kg N; balance N through urea = (120 − 23.5) / 0.46 = 210 kg. Potash through muriate of potash = 60 / 0.60 = 100 kg. Final plan: 130 kg DAP + 210 kg urea (in splits) + 100 kg MOP per hectare.
Traps
Calculating phosphorus on an elemental basis instead of P2O5; ignoring the nitrogen hidden in DAP; mixing urea with seed at sowing; and forgetting that single superphosphate also supplies sulphur and calcium.