Manures and fertilisers
Organic manures, straight and complex fertilisers, mixtures, biofertilisers and integrated nutrient management.
Manures
Manures are organic materials of plant or animal origin. They supply nutrients in small amounts, add organic matter and improve soil structure, water-holding capacity and microbial activity.
- Bulky organic manures: farmyard manure (FYM, roughly 0.5% N, 0.2% P₂O₅, 0.5% K₂O), compost, vermicompost and green manure (e.g. sunnhemp, dhaincha ploughed in at flowering).
- Concentrated organic manures: oilcakes (neem, groundnut), bone meal, fish meal; higher nutrient content.
Fertilisers
Fertilisers are manufactured or mined materials with a high, fixed nutrient content.
- Straight fertilisers supply one primary nutrient: urea (46% N), ammonium sulphate (about 20.6% N), single super phosphate (16% P₂O₅), muriate of potash (MOP, 60% K₂O).
- Complex fertilisers contain two or more primary nutrients chemically combined: DAP (18% N, 46% P₂O₅), and NPK grades such as 10:26:26.
- Fertiliser mixtures are physical blends of straight fertilisers.
Calculating a dose
Quantity of fertiliser = nutrient required × 100 ÷ % nutrient in fertiliser. Example: to supply 92 kg N with urea, 92 × 100 ÷ 46 = 200 kg urea.
Biofertilisers
Biofertilisers are living micro-organisms that add or mobilise nutrients:
- Rhizobium: symbiotic N fixation in legumes.
- Azotobacter, Azospirillum: free-living or associative N fixers for cereals.
- Blue-green algae (Anabaena, Nostoc) and Azolla (with Anabaena) in rice fields.
- PSB (phosphate solubilising bacteria) and mycorrhiza improve phosphorus uptake.
Integrated Nutrient Management (INM)
INM combines organic manures, fertilisers and biofertilisers in the right proportion to maintain soil fertility and give sustained yields. It avoids nutrient imbalance caused by using only urea, improves soil health and lowers cost.
Key points
- Urea 46% N; DAP 18:46:0; SSP 16% P₂O₅; MOP 60% K₂O.
- Straight = one nutrient; complex = two or more chemically combined.
- Green manures: sunnhemp and dhaincha.
- Azolla–Anabaena is used in rice.
- INM blends all nutrient sources.
Exam tips
- Practise the formula; numerical questions are common.
- When DAP is used, account for the N it supplies before adding urea.