Manures and Fertilizers
What the domain tests
Manures and Fertilizers tests the difference between bulky organic manures and concentrated fertilizers, fertilizer grades, methods and timing of application, and biofertilizers. Numerical questions on nutrient conversion are common.
Core rules
- FYM, compost, vermicompost, green manure and oilcakes are organic manures: low nutrient concentration, high organic matter, slow release.
- Fertilizers are classified as straight (one nutrient), complex (two or more nutrients in chemical combination) and mixed (physically blended). Examples: urea (46% N), SSP (16% P2O5 plus S and Ca), DAP (18-46-0), MOP (60% K2O).
- Fertilizer grade is expressed as %N-%P2O5-%K2O, not elemental P or K.
- Methods: basal placement, top dressing, band placement, fertigation and foliar spray. Split N application reduces leaching loss.
- Biofertilizers: Rhizobium for legumes, Azotobacter/Azospirillum for non-legumes, phosphate-solubilising bacteria for P.
- INM combines organic, inorganic and biological sources for balanced supply.
Worked example
How much urea supplies 60 kg N/ha? Urea is 46% N, so urea = 60 x 100/46 = 130.4 kg/ha. Reasoning: the numerator is the nutrient needed; divide by the fraction of nutrient in the product. If the recommendation is split 50% basal and 50% top dress, apply about 65 kg/ha at each time.
Traps
A 100 kg bag of DAP (18-46-0) supplies 18 kg N and 46 kg P2O5, not 46 kg N. Do not confuse P2O5 with P; the conversion factor is 2.29. Do not mix urea with DAP for storage without checking compatibility. Organic manure is not a complete substitute for a deficient nutrient.