Comprehensive Notes on Manures, Fertilizers, and Soil Fertility Management

Introduction and Importance of Organic Manures

• Definition of Manures: Materials organic in origin, bulky or concentrated, capable of supplying plant nutrients and improving the soil physical environment. They have no definite chemical composition and low analytical value, produced from animal, plant, and organic wastes.

• Major Sources of Manures:

  • Cattle shed wastes: Dung, urine, biogas slurry.

  • Human wastes: Night soil, urine, town refuse, sewage, and sludge.

  • Poultry/Small Ruminants: Poultry litter, sheep and goat droppings.

  • Slaughterhouse wastes: Bone meal, meat meal, blood meal, horn/hoof meal.

  • Industry By-products: Oil cakes, bagasse, press mud.

  • Crop wastes: Sugarcane trash, stubbles, coir waste.

  • Others: Water hyacinth, weeds, tank silt, green manure.

• Impact on Soil Productivity:

  • Physical: Improves structure, water holding capacity (WHC), porosity; decreases bulk density and soil temperature; prevents crusting.

  • Chemical: Supplies all essential nutrients ($N, P, K$, etc.); improves Cation Exchange Capacity (CEC) and buffering capacity; increases colloidal properties.

  • Biological: Increases microbial population/activity; organic acids formed during decomposition act as chelating agents to make nutrients available; enhances $N$ fixation and $P$ solubilization.

Classification and Properties of Organic Manures

• Bulky Organic Manures: Contain small nutrient percentages, applied in large quantities.

  • Farmyard Manure (FYM): Decomposed mixture of dung, urine, litter, and fodder leftovers.

    • Nutrient content: $0.5\text{--}1.5\% N$, $0.4\text{--}0.8\% P<em>{2}O</em>{5}$, and $0.5\text{--}1.9\% K_{2}O$.

    • Residual effect: Nutrients released slowly, benefiting succeeding crops.

    • Handling losses: Nitrogen lost as ammonia ($NH_{3}$) through volatilization and leaching from open pits.

  • Sheep and Goat Manure: Higher nutrients than FYM ($3\% N, 1\% P<em>{2}O</em>{5}, 2\% K_{2}O$). Applied via pitting or "sheep penning" (keeping animals overnight in the field).

  • Poultry Manure: Highly fermentable. Deep litter contains $3\% N, 2\% P<em>{2}O</em>{5}, 2\% K_{2}O$.

• Concentrated Organic Manures: Contain higher nutrient percentages (typically >2\% N).

  • Oil Cakes: Richest organic sources. Classified as Edible (e.g., groundnut cake $7.3\% N$) or Non-Edible (e.g., castor cake $4.3\% N$, Neem cake $5.2\% N$).

  • Slaughterhouse Products:

    • Blood meal: $10\text{--}12\% N$.

    • Meat meal: $10.5\% N$.

    • Horn/Hoof meal: $13\% N$.

• Fortified Organics: Enriching organic manures with inorganic fertilizers or biofertilizers. This reduces bulkiness and narrows the $C:N$ ratio.

Composting Techniques and Methods

• Definition: Biological conversion of organic wastes into amorphous, dark brown colloidal humus.

• Techniques:

  • Aerobic: Full oxidation, no foul smell, faster. End products: $CO_{2}$, water, energy.

  • Anaerobic: Absence of oxygen, offensive odor, slower. End products: Organic acids.

• Specific Methods:

  • ADCO Process: Uses $(NH<em>{4})</em>{2}SO_{4}$ and lime as starters.

  • Indore Method: Anaerobic; requires turning the heap at 2, 4, and 8 weeks.

  • Bangalore Method (Dr. C.N. Acharya): Overcomes smell/fly issues by layering refuse and night soil; requires no turning (anaerobic after initial aerobic phase).

  • Coimbatore Method: Pits layered with waste and dung slurry, enriched with bone meal.

• Vermicomposting: Using earthworms (e.g., Eudrillus eugenial, Eisenia foetida) to decompose waste.

  • Worms produce humic acids and stabilized mucoproteins.

  • Average nutrients: $0.5\text{--}1.5\% N, 0.1\text{--}0.3\% P, 0.15\text{--}0.56\% K$.

Green Manuring and Green Leaf Manuring

• Green Manuring (In situ): Growing and ploughing undecomposed green plant tissue into the same field (e.g., Sesbania aculeata, Sunnhemp).

• Green Leaf Manuring: Collecting green leaves/twigs from shrubs/trees and incorporating them (e.g., Gliricidia, Neem, Pongamia).

• Advantages: Increases $N$ (legumes), improves CEC, acts as a cover crop against erosion, and reclaims alkaline soils.

• Constraints: Proper decomposition requires adequate moisture; may liberate toxic gases like methane ($CH_{4}$) if not handled correctly.

Soil Carbon Sequestration and Carbon Trading

• Carbon Sequestration: Capturing and long-term storage of atmospheric $CO_{2}$ in stable solid forms (oceanic, pedologic, biotic).

• Modes:

  • Direct: Inorganic chemical reactions forming carbonates ($CaCO<em>{3}$, $MgCO</em>{3}$).

  • Indirect: Photosynthesis converting $CO_{2}$ to biomass, then to Soil Organic Carbon (SOC).

• Management Practices: Reduced tillage, cover crops, agroforestry, and Biochar application (recalcitrant charred biomass residue).

• Carbon Trading: Market-based system establishing emission limits.

  • Kyoto Protocol: Established mechanisms like Clean Development Mechanism (CDM) and Emissions Trading.

  • Cap and Trade: Companies/countries purchase rights to emit units from those with surplus capacity (reduction credits).

Chemical Fertilizers: Classification and Major Nutrients

• Classification:

  • Straight: Supply one primary nutrient ($Urea$, $MOP$).

  • Complex: Chemical combinations of two or more nutrients ($DAP$).

  • Mixed: Physical mixtures of straight fertilizers.

• Nitrogenous Fertilizers:

  • Ammoniacal: $(NH<em>{4})</em>{2}SO_{4}$ ($20.6\% N$). Acidic residual effect. Adsorbed by soil colloids.

  • Nitrate: $NaNO_{3}$ ($16\% N$). Basic effect. Highly mobile/leachable.

  • Ammoniacal and Nitrate: CAN ($25\% N$). Neutral.

  • Amide: Urea ($46\% N$). Synthetic organic. Undergoes hydrolysis: $NH<em>{2}CONH</em>{2} + 2H<em>{2}O \rightarrow (NH</em>{4})<em>{2}CO</em>{3}$.

• Phosphatic Fertilizers:

  • Water Soluble: Single Super Phosphate (SSP) ($16\% P<em>{2}O</em>{5}$). Readily available as $H<em>{2}PO</em>{4}^{-}$.

  • Citric Acid Soluble: Basic Slag ($14\text{--}18\% P<em>{2}O</em>{5}$). Suitable for acid soils.

  • Insoluble: Rock Phosphate ($20\text{--}40\% P$). Requires acidic conditions for availability.

• Potassic Fertilizers:

  • Muriate of Potash (KCl): $60\% K_{2}O$. High chlorine; avoid for tobacco/potato.

  • Sulphate of Potash ($K<em>{2}SO</em>{4}$): $48\text{--}50\% K_{2}O$. Preferred for quality-sensitive crops.

Secondary and Micronutrient Management

• Secondary Nutrients:

  • Calcium ($Ca$): Sources include Gypsum ($23.3\% Ca$) and Lime. Deficiency causes Blossom End Rot (tomato) and Bitter Pit (apple).

  • Magnesium ($Mg$): Central atom of chlorophyll. Sources: Epsom salt, Dolomite. Deficiency causes sand-drown in tobacco and "Grass Tetany" in cattle.

  • Sulphur ($S$): Essential for amino acids (Cystine, Methionine). Sources: SSP, Pyrites, Elemental $S$.

• Micronutrients ($Zn, Fe, Mn, Cu, B, Mo, Cl, Ni$):

  • Zinc: Deficiency causes "Khaira" disease in rice and "White Bud" in maize.

  • Iron: Interveinal chlorosis in young leaves. High in anaerobic rice (Bronzing).

  • Boron: Essential for cell wall stabilization and pollination. Deficiency causing "Heart Rot" (sugarbeet) and cracked stem (celery).

  • Molybdenum: Required for Nitrogenase. Availability increases with soil pH (unlike other metals).

• Chelated Micronutrients: Cations ($Fe, Zn, Cu, Mn$) bonded to organic ligands (EDTA, DTPA) to prevent precipitation and increase uptake efficiency.

Soil Fertility Evaluation and Nutrient Management Concepts

• Liebig’s Law of Minimum: Yield is limited by the nutrient present in the least relative amount.

• Mitscherlich’s Law: Yield increase is proportional to the decrement from the maximum yield ($Y = A (1 - 10^{-Cx})$).

• Bray’s Concept:

  • Mobile Nutrients: Move by mass flow ($NO_{3}^{-}$). Availability depends on total soil supply.

  • Immobile Nutrients: Move by diffusion ($P, K$). Availability depends on the root surface sorption zone.

• Soil Testing: Chemical extraction to estimate nutrient supplying power.

  • Ratings: Low (<280\text{ kg N/ha}), Medium ($280\text{--}450$), High (>450).

• Techniques:

  • STCR (Soil Test Crop Response): Targeted yield approach based on nutrient requirement per quintal of grain.

  • DRIS: Diagnosis and Recommendation Integrated System based on nutrient ratios ($N/P, N/K$).

  • Fertigation: Applying water-soluble fertilizers through drip irrigation. Efficiency: $N (95\%), P (45\%), K (80\%)$.

• 4R Concept: Right Source, Right Rate, Right Time, Right Place.

Fertilizer Control Order (FCO) and Storage

• FCO 1985: Regulates distribution, quality specifications, and pricing of fertilizers in India.

• Storage Rules:

  • Indoor: At least 1-meter away from walls/roof; never mix incompatible materials (e.g., Urea and CAN).

  • Outdoor: Use pallets; store in pyramid form; cover with tarpaulin.

• Standard specifications:

  • Urea: Max moisture $1\%$, Min Nitrogen $46\%$, Max Biuret $1.5\%$.

  • SSP: Min water-soluble $P<em>{2}O</em>{5} 16\%$.

Special Management Situations

• Dryland Agriculture: Nutrient management is limited by water scarcity and soil erosion. Requires split application, deep placement, and foliar feeding.

• Long-Term Fertilizer Experiments (LTFE): Multi-decade studies showing that Integrated Nutrient Management (INM: 100% NPK + FYM) is the only way to sustain yield and soil health without heavy metal toxicity or soil degradation.