Manures, Fertilizers and Soil Fertility Management
Fertility questions test the difference between manures and fertilizers, the nutrient content of common fertilizers, deficiency symptoms and the calculation of fertilizer doses.
Manures vs fertilizers
- Manures: FYM (about 0.5% N, 0.2% P, 0.5% K), compost, vermicompost, green manure (dhaincha, sunhemp), oil cakes. They add humus, improve soil structure and supply micronutrients but are bulky and dilute.
- Fertilizers: urea 46% N, DAP 18% N + 46% P₂O₅, SSP 16% P₂O₅ with sulphur and calcium, MOP (KCl) 60% K₂O, ammonium sulphate 21% N, and NPK complexes such as 10:26:26 and 12:32:16.
- Types: straight, complex and mixed fertilizers; concentrated and dilute.
Deficiency symptoms
N - older leaves pale, stunted plants; P - purple leaves, weak roots; K - scorched leaf margins; Zn - khaira in paddy, white bud in maize; Fe - interveinal chlorosis of young leaves; B - hollow stem and poor seed set.
Worked example
A recommendation of 120 kg N, 60 kg P₂O₅ and 40 kg K₂O per ha. DAP for P = 60 ÷ 0.46 = 130 kg, which also supplies 130 × 0.18 = 23 kg N. Urea = (120 − 23) ÷ 0.46 = 211 kg. MOP = 40 ÷ 0.60 = 67 kg. Apply half the nitrogen with all P and K at sowing, and the rest with the first irrigation.
Traps that cost marks
- Dividing by 46 instead of by 0.46, or multiplying where you should divide.
- Forgetting the nitrogen hidden inside DAP.
- Calling FYM a fertilizer; it is a manure.
- Applying a blanket dose without a soil test.