🌱 Manures, Fertilizers & Nutrient Management
Manures, fertilizers, green manuring, biofertilizers, soil amendments, application methods, INM for CUET Agriculture
Maintaining soil fertility requires a balanced approach to nutrient supply. This lesson covers the full spectrum — from traditional organic manures to modern chemical fertilizers, biological agents, and integrated strategies. Understanding the differences, advantages, and appropriate use of each source is essential for both farming practice and CUET preparation.
Manures
Manures are bulky organic materials of plant or animal origin that supply nutrients slowly over time and simultaneously improve soil physical properties (structure, water-holding capacity, aeration). Unlike chemical fertilizers, manures enhance the overall "health" of the soil, not just its nutrient content.
Bulky Organic Manures
| Type | NPK Content | Key Features |
|---|---|---|
| Farmyard Manure (FYM) | 0.5-0.3-0.5% N-P₂O₅-K₂O | Cattle dung + urine + litter; most common organic manure in India |
| Compost | 0.5-0.15-0.5% | Decomposed plant residues; several standardized methods (Indore, NADEP, Bengaluru) |
| Vermicompost | 1.5-0.4-0.8% | Earthworm-processed waste; Eisenia fetida is the most commonly used species; nutrient-rich and well-structured |
| Night soil compost | 1.0-0.8-0.5% | Human waste after proper composting; safety concerns limit its use |
NOTE
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Maintaining soil fertility requires a balanced approach to nutrient supply. This lesson covers the full spectrum — from traditional organic manures to modern chemical fertilizers, biological agents, and integrated strategies. Understanding the differences, advantages, and appropriate use of each source is essential for both farming practice and CUET preparation.
Manures
Manures are bulky organic materials of plant or animal origin that supply nutrients slowly over time and simultaneously improve soil physical properties (structure, water-holding capacity, aeration). Unlike chemical fertilizers, manures enhance the overall "health" of the soil, not just its nutrient content.
Bulky Organic Manures
| Type | NPK Content | Key Features |
|---|---|---|
| Farmyard Manure (FYM) | 0.5-0.3-0.5% N-P₂O₅-K₂O | Cattle dung + urine + litter; most common organic manure in India |
| Compost | 0.5-0.15-0.5% | Decomposed plant residues; several standardized methods (Indore, NADEP, Bengaluru) |
| Vermicompost | 1.5-0.4-0.8% | Earthworm-processed waste; Eisenia fetida is the most commonly used species; nutrient-rich and well-structured |
| Night soil compost | 1.0-0.8-0.5% | Human waste after proper composting; safety concerns limit its use |
NOTE
Vermicompost has significantly higher nutrient content than regular compost or FYM because earthworms concentrate nutrients as they pass organic matter through their gut. It also contains beneficial microorganisms and plant growth hormones.
Concentrated Organic Manures
These have higher nutrient content than bulky manures and are applied in smaller quantities:
| Type | N Content | Key Features |
|---|---|---|
| Oil cakes | 2-7% N | Neem cake serves a dual role (manure + pest control through neem's insecticidal properties); also castor cake, groundnut cake |
| Blood meal | 10-12% N | Slaughterhouse by-product; quick-acting due to high N content |
| Bone meal | 3-4% N + 20-25% P₂O₅ | Rich in phosphorus and calcium; slow-release P source |
| Fish meal | 4-10% N | Used in coastal areas; also supplies P |
Green Manuring
Green manuring is the practice of growing or bringing in green plant material and incorporating (ploughing) it into the soil to improve fertility:
| Type | Description | Examples |
|---|---|---|
| In-situ green manuring | Growing a crop in the field and ploughing it in before the main crop | Dhaincha (Sesbania aculeata), Sunnhemp (Crotalaria juncea) |
| Green leaf manuring | Bringing leaves/twigs from outside and incorporating them | Gliricidia, Pongamia, Cassia |
IMPORTANT
- Dhaincha (Sesbania aculeata) is the most popular green manure crop in India due to its fast growth, high biomass, and ability to fix nitrogen
- Green manuring adds 60-80 kg N/ha and significantly improves soil structure
- Best time to incorporate: At flowering stage — this is when biomass is maximum but the plant is still tender enough to decompose quickly
Composting Methods
Different composting methods have been developed to suit various conditions. Each has a distinct approach and timeline:
| Method | Developer | Key Feature |
|---|---|---|
| Indore method | Albert Howard (1924) | Aerobic; material is turned every 15 days for aeration; ready in 4-5 months |
| Bengaluru method | C.N. Acharya | Combined Anaerobic (trench) + Aerobic; takes 6-8 months |
| NADEP method | Narayan Deorao Pandharipande | Brick tank; layered with soil + dung + plant material; ready in 90-120 days |
| Coimbatore method | TNAU | Uses dry waste + cow dung + urine earth |
Indore vs Bengaluru method — What's the difference?
The **Indore method** (by Sir Albert Howard at the Institute of Plant Industry, Indore) is primarily **aerobic** — the compost heap is built above ground and turned regularly to supply oxygen. This produces faster decomposition but requires more labour. The **Bengaluru method** starts as **anaerobic** (material placed in a trench and covered) for 2-3 months, then the semi-decomposed material is taken out and heaped for aerobic decomposition. It requires less labour but takes longer (6-8 months total).Fertilizers
Fertilizers are manufactured chemicals that supply nutrients in concentrated, readily available form. While they provide quick nutrition, they do not improve soil physical properties and can degrade soil health if used excessively without organic supplements.
Nitrogenous Fertilizers
| Fertilizer | N Content | Form | Special Features |
|---|---|---|---|
| Urea | 46% N | Amide | Most widely used fertilizer globally; white granules; hygroscopic |
| Ammonium Sulphate | 20.6% N | Ammonium | Also supplies 24% S; acidifying effect on soil (good for alkaline soils, problematic for acidic soils) |
| CAN (Calcium Ammonium Nitrate) | 25% N | Ammonium + Nitrate | Non-acidifying; suitable for acidic soils; contains both quick-acting (NO₃⁻) and slow-acting (NH₄⁺) N |
| Ammonium Chloride | 25% N | Ammonium | Suitable for rice; avoid for tobacco, potato (Cl damages quality) |
| Anhydrous Ammonia | 82% N | Gas (liquid under pressure) | Highest N content of any fertilizer; must be injected into soil; requires specialized equipment |
| Neem-coated Urea | 46% N | Amide | Mandatory in India since 2015; neem coating slows N release, reducing losses by 10-15% |
| Nano Urea (IFFCO) | 4% N | Liquid | Foliar spray; launched 2021; 500 mL bottle claims to replace one bag (45 kg) of conventional urea |
TIP
Memory aid for N content: Anhydrous Ammonia (82%) > Urea (46%) > CAN/NH₄Cl (25%) > Ammonium Sulphate (20.6%). The "82-46-25-21" sequence is worth memorizing.
Phosphatic Fertilizers
| Fertilizer | P₂O₅ Content | Solubility | Special Features |
|---|---|---|---|
| Single Super Phosphate (SSP) | 16% | Water soluble | Also supplies 12% S and 21% Ca — a multi-nutrient fertilizer |
| Di-Ammonium Phosphate (DAP) | 46% + 18% N | Water soluble | Most popular phosphatic fertilizer in India |
| Triple Super Phosphate (TSP) | 46% | Water soluble | Concentrated P; no S or N |
| Rock Phosphate | 20-40% | Insoluble in water | Direct use only in acidic soils (pH < 5.5) where soil acids dissolve it slowly |
Potassic Fertilizers
| Fertilizer | K₂O Content | Special Features |
|---|---|---|
| Muriate of Potash (MOP/KCl) | 60% | Most common K fertilizer globally; avoid for tobacco, potato (Cl-sensitive crops) |
| Sulphate of Potash (SOP/K₂SO₄) | 50% | For Cl-sensitive crops; also supplies 18% S; more expensive than MOP |
WARNING
Chloride-sensitive crops (tobacco, potato, grapes, citrus) should receive SOP instead of MOP. Chloride from MOP reduces the quality of tobacco (affects burning quality) and potato (reduces starch content and increases water content).
Complex/Mixed Fertilizers
| Fertilizer | N-P-K Grade | Features |
|---|---|---|
| DAP | 18-46-0 | Most popular; supplies both N and P |
| NPK Complex | 12-32-16, 10-26-26, 20-20-0 | Multiple nutrients in one granule; convenient for farmers |
Fertilizer Application Methods
The method of application significantly affects nutrient use efficiency:
| Method | Description | Best For |
|---|---|---|
| Broadcasting | Spreading uniformly over the entire field | Basal application of P and K before sowing |
| Placement | Applying near plant roots (band/ring/pocket placement) | P fertilizers (reduces fixation by limiting soil contact) |
| Top dressing | Applying to standing crop during growth | N fertilizers in 2-3 splits for sustained supply |
| Foliar application | Spraying nutrient solution on leaves | Micronutrients; 2% urea spray for quick N boost |
| Fertigation | Fertilizers dissolved in drip irrigation water | Most efficient method — nutrients delivered directly to root zone |
Fertilizer Use Efficiency
A significant portion of applied fertilizer is lost before plants can use it:
| Nutrient | Efficiency | Major Loss Pathways |
|---|---|---|
| Nitrogen | 30-50% | Volatilization (NH₃), leaching (NO₃⁻), denitrification (N₂) |
| Phosphorus | 15-25% | Fixation by Fe/Al oxides (acidic soils) and Ca (alkaline soils) |
| Potassium | 50-70% | Fixation by clay minerals (especially illite), leaching in sandy soils |
NOTE
These low efficiencies mean that much of the fertilizer farmers apply (and pay for) is wasted. This is why Integrated Nutrient Management, split applications, and precision methods like fertigation are so important.
Fertilizer Calculation
A practical skill for every agriculturist:
Quantity of fertilizer = (Nutrient required in kg/ha) / (% nutrient in fertilizer) × 100
Worked Example: Calculating urea requirement
If the recommendation is **120 kg N/ha** using Urea (46% N):Urea needed = (120 / 46) × 100 = 260.8 kg/ha (approximately 261 kg or about 5.8 bags of 45 kg each)
Similarly, if you need 60 kg P₂O₅/ha using DAP (46% P₂O₅):
DAP needed = (60 / 46) × 100 = 130.4 kg/ha
Note: DAP also contains 18% N, so this application also provides 130.4 × 0.18 = 23.5 kg N/ha, which should be deducted from the N recommendation.
Biofertilizers
Biofertilizers are preparations containing living microorganisms that enhance nutrient availability when applied to soil, seed, or plant surfaces. They are a biological alternative (or supplement) to chemical fertilizers.
Nitrogen-Fixing Biofertilizers
| Biofertilizer | Organism | Type of Fixation | Target Crop | N Fixed |
|---|---|---|---|---|
| Rhizobium | Rhizobium spp. | Symbiotic (root nodules) | Legumes only | 50-200 kg N/ha/year |
| Azotobacter | A. chroococcum | Free-living | Non-legumes (cereals, vegetables) | 20-40 kg N/ha |
| Azospirillum | A. lipoferum, A. brasilense | Associative (with roots) | Cereals (rice, wheat, maize) | 20-40 kg N/ha |
| Blue-Green Algae (BGA) | Anabaena, Nostoc | Free-living/symbiotic | Rice (wetland) | 20-30 kg N/ha |
| Azolla | Azolla pinnata + Anabaena azollae | Symbiotic (fern + alga) | Rice | 40-60 kg N/ha |
| Acetobacter | Gluconacetobacter diazotrophicus | Endophytic (lives inside plant) | Sugarcane | 30-50 kg N/ha |
Phosphate Biofertilizers
| Biofertilizer | Organism | Function |
|---|---|---|
| PSB (Phosphate Solubilizing Bacteria) | Bacillus, Pseudomonas | Solubilize fixed/insoluble P through production of organic acids (citric, oxalic, gluconic acid) |
| Mycorrhiza (VAM) | Glomus spp. (fungi) | Enhance P uptake by extending the root system with fungal hyphae; also improve drought tolerance |
IMPORTANT
Key points on biofertilizers:
- Rhizobium is host-specific — different strains are needed for different legumes (e.g., Rhizobium leguminosarum for peas, Bradyrhizobium japonicum for soybean)
- Biofertilizers reduce chemical fertilizer requirement by 25-30%
- Stored in carrier material (lignite or charcoal-based); shelf life approximately 6 months
- Application methods: Seed treatment (10 g/kg seed), soil application, or seedling root dip
- Should NOT be mixed with chemical fertilizers or fungicides (chemicals kill the microorganisms)
Mycorrhiza (VAM) — How it works
**Vesicular-Arbuscular Mycorrhiza (VAM)** is a symbiotic association between plant roots and fungi of the genus *Glomus*. The fungal hyphae extend far beyond the root zone into surrounding soil, effectively increasing the root's "reach" by 10-100 times. This is especially beneficial for **phosphorus uptake** because P is immobile in soil and quickly gets depleted in the immediate root zone. The fungus provides P (and water) to the plant, while the plant provides carbohydrates (sugars from photosynthesis) to the fungus. VAM also improves **drought tolerance** and provides some protection against root pathogens.Soil Amendments for Problem Soils
Different problem soils require different amendments. Choosing the wrong amendment can worsen the problem:
Acidic Soils (pH < 6.0)
| Amendment | Application |
|---|---|
| Agricultural lime (CaCO₃) | Most common; neutralizes acidity by providing OH⁻ ions |
| Dolomite (CaCO₃·MgCO₃) | When both Ca and Mg are deficient — provides both nutrients |
| Basic slag | By-product of steel industry; supplies Ca and P along with neutralizing acidity |
- Apply lime 2-4 weeks before sowing to allow it to react with soil; incorporate into the top 15 cm of soil
Alkaline/Sodic Soils (pH > 8.5, ESP > 15)
| Amendment | Application |
|---|---|
| Gypsum (CaSO₄·2H₂O) | Most common for sodic soils; Ca²⁺ replaces Na⁺ on clay particles → improves structure |
| Sulphur | Oxidized to H₂SO₄ by Thiobacillus bacteria → acidifies soil |
| Press mud | By-product of sugar industry; rich in Ca and organic matter |
| Iron pyrites | Source of sulphur; oxidized in soil to produce sulphuric acid |
- Leaching with good quality water is essential after gypsum application to wash displaced Na⁺ out of the root zone
Saline Soils (EC > 4 dS/m)
Saline soils have excess soluble salts but generally good structure (salts promote flocculation). Reclamation approach:
- Primary method: Leaching with good quality water (flush salts below root zone)
- Provide adequate drainage to carry away leached salts
- Grow salt-tolerant crops: Barley, Beet, Cotton, Date palm, Rice
TIP
Quick summary: Acidic soil → Lime; Sodic soil → Gypsum + Leaching; Saline soil → Leaching + Drainage. Do not confuse these — gypsum is for sodic (Na problem), not saline (salt problem).
Integrated Nutrient Management (INM)
Definition
INM is the combined and judicious use of organic manures, chemical fertilizers, and biofertilizers to maintain soil fertility, sustain crop productivity, and minimize environmental pollution. It represents the most balanced and sustainable approach to plant nutrition.
Principles of INM
- Use organic sources as base nutrition (FYM, compost, green manure) — these build long-term soil health
- Supplement with chemical fertilizers for balanced nutrition based on soil testing
- Include biofertilizers for biological nutrient cycling
- Apply site-specific nutrient management using the STCR (Soil Test Crop Response) approach
- Recycle crop residues and agricultural wastes back into the field
Recommended INM Package (General)
- 50% N through organic sources (FYM/compost/green manure)
- 50% N through chemical fertilizers (urea/DAP)
- Full P and K through fertilizers based on soil test
- Seed/soil inoculation with appropriate biofertilizers
- Micronutrient spray based on deficiency symptoms
Benefits of INM
- Maintains long-term soil fertility and productivity (organic matter sustains soil biology)
- Reduces cost and dependence on chemical fertilizers
- Improves soil physical, chemical, and biological properties simultaneously
- Reduces environmental pollution (less leaching, runoff of chemicals)
- Ensures balanced plant nutrition and better crop quality
Important Fertilizer Policies and Schemes (India)
Government policies shape fertilizer use patterns across the country:
| Scheme/Policy | Year | Key Feature |
|---|---|---|
| Nutrient Based Subsidy (NBS) | 2010 | Subsidy based on P, K, S content; urea remains under separate price control (leading to overuse of N) |
| Soil Health Card Scheme | 2015 | Soil testing and nutrient recommendations for every farm; aims for balanced fertilization |
| Neem-coated Urea (mandatory) | 2015 | 100% urea must be neem-coated; reduces N loss by 10-15%; prevents diversion to industrial use |
| Nano Urea (IFFCO) | 2021 | Liquid nano urea; 4% N; foliar spray; 500 mL claimed to replace one 45 kg bag of urea |
| One Nation One Fertilizer | 2022 | All subsidized fertilizers sold under "Bharat" brand regardless of manufacturer |
| PM-PRANAM | 2023 | Incentivizes states to promote balanced and reduced fertilizer use |
NOTE
India's actual N:P:K consumption ratio is heavily skewed towards nitrogen (approximately 7:2.7:1 in many regions) compared to the ideal ratio of 4:2:1. This imbalance degrades soil health and reduces fertilizer efficiency. Policies like NBS and PM-PRANAM aim to correct this.
Key Points for CUET
Quick Revision Checklist
- **Liebig's Law of Minimum:** Crop yield is limited by the nutrient present in the **least amount** (weakest link in the chain) - **17 essential elements** — 3 from air/water, 6 macronutrients, 8 micronutrients - Mobile nutrients: deficiency in **old leaves**; Immobile: deficiency in **young leaves** - **Urea (46% N)** — most used fertilizer; **DAP (18-46-0)** — most popular P fertilizer - **Rhizobium** for legumes (host-specific); **Azotobacter** for non-legumes (free-living) - **Mycorrhiza (VAM)** enhances P uptake through extended fungal hyphae - **Lime** for acidic soils; **Gypsum** for sodic soils; **Leaching** for saline soils - **INM** = Organic + Chemical + Biological sources combined - India's ideal N:P:K ratio is **4:2:1**; actual is heavily skewed towards N - **Khaira disease** in rice = Zinc deficiency; **Whiptail** in cauliflower = Molybdenum deficiency - **Dhaincha** = Most popular green manure; **Albert Howard** = Indore composting method - Neem-coated urea mandatory since 2015; Nano Urea launched 2021Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| Manures | Bulky organic materials; supply nutrients slowly; improve soil physical properties |
| FYM (Farmyard Manure) | 0.5-0.3-0.5% N-P₂O₅-K₂O; cattle dung + urine + litter; most common organic manure in India |
| Vermicompost | 1.5-0.4-0.8% NPK; earthworm (Eisenia fetida) processed; higher nutrient than FYM/compost |
| Blood meal | 10-12% N — highest among concentrated organic manures; quick-acting |
| Bone meal | 3-4% N + 20-25% P₂O₅; rich in P and Ca; slow-release |
| Green manuring — In-situ | Growing + ploughing in field; Dhaincha (Sesbania aculeata) = most popular; adds 60-80 kg N/ha |
| Green manuring — Green leaf | Bringing leaves from outside; Gliricidia, Pongamia |
| Incorporate green manure | At flowering stage (max biomass, still tender) |
| Indore composting | Albert Howard (1924); aerobic; turned every 15 days; ready 4-5 months |
| Bengaluru composting | C.N. Acharya; anaerobic + aerobic combined; 6-8 months |
| NADEP composting | Brick tank; layered soil + dung + plant material; ready 90-120 days |
| Urea | 46% N; most widely used fertilizer globally; amide form |
| Anhydrous Ammonia | 82% N — highest N content of any fertilizer; gas (liquid under pressure) |
| Ammonium Sulphate | 20.6% N + 24% S; acidifying effect |
| CAN | 25% N; non-acidifying; suitable for acidic soils |
| Neem-coated Urea | Mandatory in India since 2015; reduces N loss by 10-15% |
| Nano Urea (IFFCO) | Launched 2021; liquid foliar spray; 500 mL replaces one 45 kg bag |
| SSP | 16% P₂O₅ + 12% S + 21% Ca; multi-nutrient |
| DAP | 18% N + 46% P₂O₅; most popular P fertilizer in India |
| MOP (KCl) | 60% K₂O; most common K fertilizer; avoid for tobacco, potato (Cl-sensitive) |
| SOP (K₂SO₄) | 50% K₂O + 18% S; for Cl-sensitive crops |
| Broadcasting | Uniform spreading; for basal P and K |
| Placement | Near roots (band/ring); best for P fertilizers (reduces fixation) |
| Fertigation | Fertilizer in drip water; most efficient method |
| N use efficiency | 30-50%; losses via volatilization, leaching, denitrification |
| P use efficiency | 15-25%; loss via fixation by Fe/Al (acidic) and Ca (alkaline) |
| K use efficiency | 50-70%; fixation by clay minerals |
| Fertilizer calculation | Quantity = (Nutrient needed kg/ha) / (% nutrient in fertilizer) × 100 |
| Rhizobium | Symbiotic N fixer for legumes only; host-specific; 50-200 kg N/ha |
| Azotobacter | Free-living N fixer for non-legumes; 20-40 kg N/ha |
| Azospirillum | Associative N fixer; cereals (rice, wheat); 20-40 kg N/ha |
| BGA + Azolla | Rice (wetland); BGA: 20-30 kg N/ha; Azolla + Anabaena: 40-60 kg N/ha |
| PSB | Phosphate Solubilizing Bacteria (Bacillus, Pseudomonas); produce organic acids to solubilize fixed P |
| Mycorrhiza (VAM) | Glomus fungi; enhance P uptake by extending root reach 10-100×; also improve drought tolerance |
| Biofertilizer rules | Reduce chemical fertilizer by 25-30%; shelf life ~6 months; NOT mix with chemicals/fungicides |
| Acidic soil amendment | Lime (CaCO₃) most common; dolomite when Ca + Mg both deficient; apply 2-4 weeks before sowing |
| Sodic soil amendment | Gypsum (CaSO₄·2H₂O) most common; Ca²⁺ replaces Na⁺; + leaching essential |
| Saline soil reclamation | Leaching + drainage; grow salt-tolerant crops (barley, beet, cotton, date palm, rice) |
| INM | Combined use of organic + chemical + biofertilizers; 50% N organic + 50% N chemical recommended |
| India ideal N:P:K | 4:2:1; actual is heavily skewed towards N |
| Liebig's Law of Minimum | Yield limited by nutrient present in least amount |
| NBS (2010) | Subsidy based on P, K, S content; urea under separate price control |
| Soil Health Card (2015) | Soil testing + nutrient recommendation for every farm |
| One Nation One Fertilizer (2022) | All subsidized fertilizers sold under "Bharat" brand |
| PM-PRANAM (2023) | Incentivizes states to promote balanced/reduced fertilizer use |
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