Nitrification Inhibitors
These are chemicals that slow down the conversion of ammonium (NH₄⁺) to nitrate (NO₃⁻) by inhibiting nitrifying bacteria (e.g., Nitrosomonas). Used With: Ammonia, Ammonium salts, Urea
Types Based on Land Conditions:
For Lowland:
Inhibitor | Formula | N Content (%) | Properties |
Oxamide | NH₂COCONH₂ | 31 | Not hygroscopic; sol. = 0.4g/L |
Dicyandiamide (DD) | NH₂C(=NH)NHCN | 42 | Stable and effective |
Thiourea (TU) | SC(NH₂)₂ | 36.8 | Multifunctional compound |
Urea Pyrolyzate | — | 48 | Slow release |
For Upland:
- AM: 2-amino-4-chloro-6-methyl pyrimidine
- N-Serve: 2-chloro-6-trichloromethyl pyridine
Others: ASU (Guanyl thiourea), Nitrapyrin, Sulphathiazole (ST), DCS, ATC, Neem Cake (eco-friendly)
- Slow Release Fertilizers; These are designed to release nutrients gradually to minimize leaching and loss.
✨ A. Chemically Less Soluble Compounds:
Fertilizer | N Content (%) | Notes |
Isobutylidene Diurea (IBDU) | 31–32 | Slow hydrolysis |
Crotonylidene Diurea (CDU) | 32.5 | Solubility controlled by pH |
Guanyl Urea Sulphate (GUS) | — | — |
Urea Formaldehyde (UF) | 38–42 | Less hygroscopic than urea |
Oxamide | 31 | Dual use: nitrification inhibitor & slow release |
✨ Coated Urea:
- Sulphur-coated urea
- Neem-coated urea (also acts as insect repellent)
- Lac/shellac-coated urea (34.2% N)
Modified Forms:
- Super granules/briquettes (1–4 g each)
- Placed in reduced soil zones to minimize volatilization
- Biofertilizers / Microbial Inoculants
Definition: Preparations containing live or latent microorganisms (e.g., N-fixers, P-solubilizers, decomposers) that promote nutrient availability.
Types of Applications:
(a) Seed Inoculants:
- Moong, Arhar, Lentil: 500g Rhizobium/ha (2.5 packets)
- Groundnut: 1.5 kg/ha (7.5 packets)
- Soybean, Bengal gram: 1 kg/ha (5 packets)
(b) Soil Inoculants: 2 kg Azotobacter or Azospirillum mixed with 25 kg FYM + 25 kg soil per ha
Benefits:
- Fix 50–200 kg N/ha/year
- Leave 40–80 kg residual N
- Produce plant hormones (IAA, GA, NAA)
- Act as bio-pesticides (through antibiotics)
- Improve soil structure, fertility, water-holding
- Biological Nitrogen Fixation (BNF)
Definition: Natural process where atmospheric nitrogen (N₂) is converted to ammonia by certain microorganisms.
Source | Nitrogen Fixed (kg/ha/year) |
Legumes | 150–250 |
Actinomycetes | 50–150 |
Beans | 30–50 |
Algae (Nostoc) | 10–20 |
(a) Symbiotic Fixation
- With Legumes (Rhizobium spp.)
Rhizobium Species | Host Plant Genus |
R. meliloti | Medicago, Trigonella |
R. trifolii | Trifolium |
R. leguminosarum | Peas, Vetch, Lentil |
R. phaseoli | Beans |
R. lupini | Lupine, Serradella |
R. japonicum | Soybean, Cowpea, Groundnut, Crotalaria |
- Key protein: Leghaemoglobin — protects Nitrogenase by regulating O₂.
- N-fixation example: Lucerne > 250 kg N/ha
With Non-legumes (Frankia in actinomycetes); Found in Casuarina, Alnus, Myrica
(b) Non-Nodular Symbiosis
- Azolla–Anabaena azollae: Fixes 30–40 kg N/ha
- Thrives in pH 5.5–7.0; temp. 20–30°C
- Nursery size: 4m × 2m × 30–40 cm
(c) Non-Symbiotic Fixation
(i) Heterotrophic Bacteria:
Bacteria | Optimum pH | Note |
Azotobacter | 6.5–8.0 | Aerobic, rice/sugarcane |
Beijerinckia | 5.0–9.0 | Tropical tolerant |
Clostridium | 5.0–9.0 | Anaerobic |
Fix ~5–20 kg N/ha/year
(ii) Autotrophic Microorganisms:
- Rhodospirillum (anaerobic photosynthetic)
- Blue-green algae (Nostoc, Anabaena, Aulosira, etc.)
Key Points for Exams:
- Rhizobium is aerobic, but nitrogenase is inactivated by O₂, hence protected by leghaemoglobin.
- Azolla can be dual cropped in rice systems and acts as green manure.
- Blue-Green Algae (BGA) add 20–25 kg N/ha in lowland paddy fields.
- Neem-coated urea is a slow-release nitrogen source and acts as nitrification inhibitor + insecticide.
- Azotobacter is best suited for non-legumes like maize, sugarcane.
