Unit 4: Organic Manures and Integrated Nutrient Management

1. Introduction and Importance of Manures and Fertilizers

Soil fertility management relies on the addition of external nutrient sources to replenish nutrients removed by crop harvest, leaching, and erosion. These sources are broadly classified into manures and fertilizers.

1.1 Definitions

• Manures: Plant and animal wastes that are used as sources of plant nutrients. They release nutrients after their decomposition. They are generally bulky in nature and supply small quantities of nutrients but in large volumes.
• Fertilizers: Industrially manufactured chemical substances containing plant nutrients in known and higher concentrations. They are generally inorganic (except Urea, which is organic chemically but acts as a synthetic fertilizer).

1.2 Importance of Manures

1. Soil Physical Health: Improves soil structure, aeration, and water holding capacity (WHC). It promotes soil aggregation.
2. Nutrient Supply: Supplies all essential macro and micronutrients, though in small quantities.
3. Microbial Activity: Provides food (carbon source) for soil microorganisms, enhancing biological activity.
4. Buffering Capacity: Increases the soil's buffering capacity, preventing rapid changes in pH.
5. Sustainability: Prevents nutrient mining and maintains long-term soil health.

1.3 Importance of Fertilizers

1. High Nutrient Density: Supplies specific nutrients in large quantities to meet the immediate demand of high-yielding crop varieties.
2. Quick Release: Nutrients are available to plants almost immediately after application (except slow-release types).
3. Ease of Handling: Being concentrated, they are easier to transport and apply compared to bulky organic manures.

1.4 Differences between Manures and Fertilizers

2. Classification of Organic Manures

Organic manures are classified based on nutrient concentration:

1. Bulky Organic Manures: Low nutrient content per unit weight; applied in large quantities.
   • Examples: Farm Yard Manure (FYM), Compost, Green Manure.
2. Concentrated Organic Manures: Higher nutrient content; made from raw materials of animal or plant origin.
   • Examples: Oil-cakes, Blood meal, Bone meal, Fish meal.

3. Farm Yard Manure (FYM)

3.1 Definition

FYM is the decomposed mixture of dung and urine of farm animals along with litter (bedding material) and left-over material from roughages or fodder fed to the cattle.

3.2 Composition (Average)

• Nitrogen (N): 0.5%
• Phosphorus (P₂O₅): 0.25%
• Potassium (K₂O): 0.5%
• Note: Urine contains more N and K than dung, while dung is richer in P.

3.3 Preparation Methods

The quality of FYM depends on the method of preparation.

1. Pit/Trench Method: Digging a trench (6-7m long, 1.5m wide, 1m deep). Material is layered and plastered with mud to create anaerobic conditions. This reduces nitrogen loss (volatilization).
2. Heap Method (Common but inefficient): Piling waste on the ground. Leads to high nutrient loss due to leaching (rain) and volatilization (sun).

3.4 Properties and Uses

• Properties: Dark color, amorphous structure, C:N ratio typically ranges from 20:1 to 30:1.
• Uses: Applied 3–4 weeks before sowing to allow mineralization. Typical application rate: 10–20 tonnes/ha for field crops; higher for vegetables.

4. Compost

4.1 Definition

Compost is a mass of rotted organic matter made from waste (crop residues, vegetable peelings, weed biomass) through the action of microorganisms (bacteria, fungi).

4.2 Types and Preparation

1. Rural Compost: Made from farm residues, cattle dung, and urine earth.
2. Urban/Town Compost: Made from municipal solid waste (MSW) and sewage sludge.

Methods of Composting:

• Indore Method (Aerobic): Developed by A. Howard and Y.D. Wad. Involves turning the material regularly for aeration. Faster decomposition (3-4 months).
• Bangalore Method (Anaerobic): Developed by C.N. Acharya. Material is placed in layers in trenches and sealed with mud. No turning. Slower decomposition (6-8 months) but conserves more Nitrogen.
• NADEP Method: Developed by N.D. Pandharipande. Uses a brick structure with aeration holes. Relies on aerobic decomposition without turning.

4.3 Properties

• Rural Compost: 0.5% N, 0.15% P₂O₅, 0.5% K₂O.
• Town Compost: 1.4% N, 1.0% P₂O₅, 1.4% K₂O (Variable based on waste source).

5. Vermicompost

5.1 Concept

Vermicompost is the product of the composting process using various species of earthworms to create a mixture of decomposing vegetable or food waste, bedding materials, and vermicast. Vermicast (worm castings) is the end-product of the breakdown of organic matter by earthworms.

5.2 Preparation

• Earthworm Species: Eisenia foetida (Red wiggler) and Eudrilus eugeniae are most common.
• Process:
  1. Base layer of bedding (chopped straw/leaves).
  2. Layer of pre-decomposed organic waste.
  3. Release of earthworms.
  4. Maintenance of moisture (50-60%) and shade (worms are photosensitive).
  5. Harvesting in 45–60 days.

5.3 Properties and Nutrient Content

Vermicompost is nutritionally superior to conventional compost.

• Nitrogen: 1.5 – 3.0%
• Phosphorus: 1.0 – 1.5%
• Potassium: 1.5 – 2.5%
• Contains plant growth hormones (auxins, gibberellins) and enzymes.

5.4 Uses

• Excellent for nursery raising, pot culture, and high-value crops.
• Improves soil biological health significantly.

6. Green Manuring

6.1 Concept

Green manuring is the practice of ploughing in or turning into the soil undecomposed green plant tissues for the purpose of improving physical structure and soil fertility.

6.2 Types of Green Manuring

1. Green Manuring In-Situ: Growing green manure crops in the main field and incorporating them into the soil at the flowering stage.
   • Crops: Sunnhemp (Crotalaria juncea), Dhaincha (Sesbania aculeata), Cowpea, Cluster bean.
   • Best for: Areas with sufficient rainfall/irrigation.
2. Green Leaf Manuring (GLM): Collecting green leaves and tender twigs from trees/shrubs growing on bunds or wastelands and incorporating them into the main field.
   • Plants: Glyricidia (Glyricidia maculata), Pongamia (Pongamia pinnata), Neem.

6.3 Benefits

• Nitrogen Fixation: Leguminous green manures fix atmospheric N (approx. 60–100 kg N/ha).
• Organic Matter: Adds biomass (10–20 tonnes/ha fresh weight).
• Nutrient Mining: Deep-rooted crops (like Dhaincha) mine nutrients from lower soil layers and deposit them in the topsoil.
• Reclamation: Dhaincha is resistant to salinity and is used to reclaim saline-sodic soils.

7. Oil-Cakes and Other Concentrated Manures

Concentrated organic manures have higher nutrient content and low moisture compared to bulky manures.

7.1 Oil-Cakes

The solid residue remaining after oil extraction from seeds.

• Edible Oil Cakes: Fed to cattle; excreta is used as manure (e.g., Mustard cake, Groundnut cake).
• Non-Edible Oil Cakes: Used directly as manure (e.g., Castor cake, Neem cake, Mahua cake).

Nutrient Content (Average):

• Groundnut Cake: ~7.3% N, 1.5% P, 1.3% K.
• Neem Cake: ~5.2% N, 1.0% P, 1.4% K.

Special Property of Neem Cake: It contains alkaloids (nimbin, nimbidin) which inhibit nitrification. Coating urea with neem cake retards the conversion of NH₄⁺ to NO₃⁻, reducing Nitrogen loss via leaching and denitrification.

7.2 Other Concentrated Manures

• Blood Meal: Dried animal blood. Very rich in Nitrogen (10–12% N). Rapidly mineralized.
• Bone Meal: Ground animal bones. Rich source of Phosphorus (20–25% P₂O₅) and Calcium. Used for long-duration crops and acidic soils.
• Fish Meal: Dried fish waste. Contains 4–10% N and 3–9% P.

8. Integrated Nutrient Management (INM)

8.1 Concept

Integrated Nutrient Management (INM) refers to the maintenance of soil fertility and plant nutrient supply at an optimum level for sustaining the desired productivity through optimization of the benefits from all possible sources of plant nutrients in an integrated manner.

Core Philosophy: It moves away from exclusive reliance on chemical fertilizers, aiming instead for a balanced recipe of inorganic, organic, and biological sources.

8.2 Need for INM

1. Rising Cost: Chemical fertilizers are becoming expensive (energy-intensive).
2. Soil Health Decline: Continuous use of chemicals degrades soil structure and reduces microbial diversity.
3. Pollution: Runoff causes eutrophication; leaching pollutes groundwater.
4. Multi-Nutrient Deficiency: Exclusive NPK use leads to micronutrient (Zn, Fe, B) deficiencies.

8.3 Components of INM

INM involves the combined application of:

1. Chemical Fertilizers: Used judiciously to meet peak nutrient demands.
2. Organic Manures: FYM, Compost, Vermicompost to improve physical properties and supply micronutrients.
3. Green Manures: To add biomass and fix nitrogen.
4. Biofertilizers: Microbial inoculants that fix N or solubilize P.
   • N-fixers: Rhizobium (legumes), Azotobacter, Azospirillum (cereals), BGA/Azolla (rice).
   • P-solubilizers: PSB (Phosphorus Solubilizing Bacteria).
5. Crop Residues: Incorporation of stubble rather than burning.
6. Legumes in Rotation: Including pulses to restore soil fertility naturally.

8.4 Advantages of INM

• Synergistic Effects: Organic manures increase the efficiency of chemical fertilizers (e.g., reducing leaching losses).
• Yield Stability: Maintains high yields over long periods (sustainable agriculture).
• Cost Reduction: Reduces the total requirement of expensive chemical fertilizers.
• Environmental Safety: Minimizes soil and water pollution.
• Soil Physical Improvement: Maintains favorable soil structure, aeration, and water retention.