Comprehensive Study Material on Manures for UP TGT and PGT Agriculture

Organic manures are partially decomposed plant and animal residues applied to the soil to supply plant nutrients, improve soil physical properties, enhance water retention capacity, and stimulate beneficial microbial populations. According to ICAR classification standards, manures are broadly classified into two major categories based on their bulk density and nutrient concentration:

• Bulky Organic Manures: These are characterized by a low percentage of primary plant nutrients (N, P₂O₅, K₂O) and are applied in large quantities. Major examples include Farmyard Manure (FYM), compost (rural and urban), vermicompost, and green manures.
• Concentrated Organic Manures: These possess a higher percentage of total nitrogen, phosphorus, and potassium compared to bulky manures and are derived from plant or animal tissues. Major examples include oilcakes (edible and non-edible), blood meal, bone meal, meat meal, and fish meal.

Farmyard Manure (FYM) is a heterogeneous mixture of cattle dung, urine, and litter (bedding material such as straw or chopped crop residues). Well-decomposed FYM typically contains approximately 0.5% N, 0.2% P₂O₅, and 0.5% K₂O. Proper storage and composting methods are critical to prevent nutrient losses through leaching and volatilization:

• Nutrient Losses Prevention: Urine contains nearly half of the total nitrogen and most of the potassium present in excreta; therefore, absorption using bedding material and protected storage trenches is essential. Lignin and cellulose present in straw regulate decomposition rates.
• Composting Methods: Traditional methods include the Bangalore method (closed trench system, anaerobic decomposition) and the Indore method (aerobic heap system developed by Howard and Wad). The Indore method involves alternating layers of organic wastes, night soil, and wood ash, taking about 3 to 4 months for complete maturity.

Green manuring involves growing un-decomposed green plant tissue—usually leguminous crops—and incorporating it into the soil while still green to improve soil fertility and structure. It serves as an in-situ biological nitrogen factory:

• Popular Green Manuring Crops: Sunnhemp (Crotalaria juncea), Dhaincha (Sesbania aculeata), Cowpea (Vigna unguiculata), and Cluster bean (Cyamopsis tetragonoloba). Sesbania aculeata is exceptionally tolerant to waterlogging, salinity, and alkalinity.
• Agronomic Benefits: Green manuring adds 60 to 90 kg N ha^-1, increases organic carbon content, enhances cation exchange capacity (CEC), and mobilizes insoluble soil phosphorus through organic acid exudation. The optimum time of incorporation is usually at the flowering stage to ensure tender tissues and a favorable C:N ratio.

Vermicomposting is the biotechnological process of composting organic residues utilizing earthworm species to accelerate decomposition and produce a nutrient-rich organic amendment:

• Earthworm Species: Epigeic species such as Eisenia fetida (Red Worm), Eudrilus eugeniae (African Nightcrawler), and Perionyx excavatus are predominantly used due to their high ingestion and reproductive rates.
• Nutrient Profile: Vermicompost generally exhibits higher nutrient availability than traditional FYM, typically containing 1.5% to 2.5% N, 0.9% to 1.5% P₂O₅, and 1.2% to 1.8% K₂O, along with plant growth regulators, humic acids, and beneficial microflora.
• C:N Ratio Dynamics: Microorganisms require carbon for energy and nitrogen for protein synthesis. The critical C:N ratio for rapid decomposition is approximately 20:1 to 30:1. A wider C:N ratio (>30:1) results in microbial immobilization of soil available nitrogen, whereas a narrow ratio (<20:1) promotes rapid net mineralization and release of inorganic nitrogen into the soil solution.

Concentrated organic manures are rich in nutrient content and are widely utilized in high-value horticulture and organic field crop production:

• Edible Oilcakes: Neem (Azadirachta indica), Karanja (Pongamia pinnata), Mustard, and Groundnut cake. Mustard cake contains approximately 5.1% N, 1.8% P₂O₅, and 1.5% K₂O.
• Non-Edible Oilcakes: Castor cake, Mahua cake, and Karanja cake. These are typically toxic or unpalatable to livestock and are used directly as organic fertilizers or nitrification inhibitors. For instance, neem cake contains triterpenoids and limonoids that inhibit soil nitrification, reducing nitrate leaching losses.
• Bone Meal: Steamed bone meal is a rich source of calcium and phosphorus, containing about 20% to 25% total P₂O₅ (mostly tricalcium phosphate) and 3% to 4% N, highly effective in acidic soils.