What are Manures and Fertilizers and their Classification?

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Manures and Fertilizers – Types, Advantages, Differences

The deficiency of plant nutrients and organic matter in the soil is made up by adding manures and fertilizers to the soil of crop fields. Both manures and fertilizers are major sources of nutrients for plants, so they are used in crop production.

Manures

Manures are natural fertilizers. They are bulky sources of organic matter which supply nutrients in small quantities and organic matter in large quantities. Manures are prepared by decomposed animal excreta and plant waste. Manures include farmyard manure (FYM), compost, green manures, vermicompost, etc.

Advantages of Manures:

Manures affect the soil in the following three ways:

• Manures enrich the soil with nutrients. They replenish the general deficiency of nutrients in the soil. Since manures contain fewer nutrients they need to be used in large quantities.
• Manures add organic matter (called humus) to the soil which restores the soil texture, for better retention of water and aeration of soil. For example, organic matter present in the manures increases the water-holding capacity in sandy soils and drainage in clayey soil. They also prevent water logging in clay soils.
• The organic matter in manures provides food for the soil organisms, (decomposers such as bacteria, fungi, etc.) which help in providing nutrients to plants.

Thus organic manures help to improve the physical properties of soil, reduce soil erosion, increase the moisture-holding capacity of the soil, and are low-cost nutrient carriers. Using biological waste material is a way of recycling farm waste. Manures protect our environment from synthetic chemicals (i.e., fertilizers).

Disadvantages of Manures:

Manures are bulky with low nutrient content. The nutrients get released slowly, unable to fulfill the high and rapid demand for nutrients required by improved high-yielding hybrid varieties of crops. Being bulky and voluminous, they are inconvenient to handle, store, and transport. Moreover, manures are not nutrient specific and, hence, are not much used when a particular nutrient is required in the soil for a particular crop.

Types of Manures

Farmyard manure (FYM):
FYM is the decomposed mixture of cattle excreta, (dung), urine, litter (i.e., bedding material used at night under cattle), and leftover organic matter such as roughage, or fodder. These waste materials are collected daily from the cattle shed and stored in a pit for decomposition by microorganisms (bacteria, fungi, etc.). FYM contains nitrogen, phosphorus, and potassium. A well-decomposed farmyard manure contains about 0.5 percent nitrogen (N), 0.2 percent phosphorus pentaoxide (P₂O₅), and 0.5 percent potassium monoxide (K₂O).

Compost:
Compost is prepared from farm and town refuges such as vegetable and animal refuse (e.g., excreta of domestic animals such as cattle, goat, sheep, horse, donkey, camel, dogs, cats, etc.), fecal matter of human beings, sewage waste (Box 1.6), weeds, crop stubble, straw, rice hulls, forest litter, etc. Composting is a biological process in which both aerobic (organisms requiring the presence of oxygen for respiration) and anaerobic (organisms, in which respiration takes place in the absence of oxygen) microorganisms decompose the organic matter. It takes about 3 to 6 months for decomposition of organic refuse. The nutrient contents of town compost are about 1.4 percent nitrogen (N), 1.0 percent phosphorus pentaoxide (P₂O₅, and 1.4 percent potassium monoxide (K₂O).

Sewage:
In the modern system of sanitation, water is used for the removal of human excreta and other wastes. Sewage consists of two components: (i) The solid part, called the sludge, and (ii) the liquid part, called effluent or sewage water. The dried sludge may be used as a soil conditioner in lawns and flower gardens. Sewage water is quite rich in many nutrients for plants so can be used for fertilizing and irrigating the soil.

Method of preparing compost:

For preparing compost, a trench of suitable size, i.e., 4 to 5 m long, 1.5 to 1.8 m broad, and 1.0 to 1.8 m deep is dug. A layer of well-mixed refuse of about 30 cm thickness is spread in the trench. This layer is well moistened by slurry (water paste) of cattle dung and water or earth and water. A second layer of mixed refuse is spread in the trench till the heap rises to a height of 45 to 60 cm above ground level.

The top of this heap is then covered with a thin layer of moist earth. After three months, the partially decomposed biomass is taken out of the trench and collected in a conical heap. This heap is moistened if necessary and covered with earth. After another one or two months, the compost is ready for use in the field.

Vermicomposting
The degradation of organic waste through the consumption of earthworms is called vermicomposting. An earthworm is physically an aerator, crusher, and mixer, chemically a degraded, and biologically a stimulator of decomposition. In India, the following species of earthworms are used in vermicomposting: Dichogaster bolani, Drawida wills, Perionyx excavatus (Indian species) and Eisenia foetida, Eudrilus eugeniae (Exotic species).

Green Manure:
The practice of green manuring includes growing, mulching by ploughing, and mixing of green crops with soil, to improve the physical structure and soil fertility. A green manure crop supplies: (i) nitrogen and phosphorus; (ii) organic matter for improving the hydration, aeration, and crumb structure of the soil. It tends to provide protection against erosion and leaching.

Green manures are generally quick-growing leguminous and non-leguminous plants. Some examples of green manure plants are

• Dhaincha (Sesbania aculeata)
• Sunn Hemp (Crotalaria juncea)
• Cluster bean or guar (Cyamopsis tetragonoloba)
• Cow pea or Lobia (Vigna sinensis)
• Lentil or Masur (Lens culiriaris)
• Egyptian clover or Berseem (Trifolium alexandrium)
• Horse gram (Dolichos uniflorus)

The green manure crops are grown in the field for about 6 to 8 weeks and are overturned when in the tender stage, i.e., at the flowering stage. These crops remain buried for about one to two months. During this period, plants should be completely decomposed before sowing of next crop. Generally, the crops which require high nutrient input, are raised in a green manured field. Such crops are rice, maize, sugarcane, cotton, wheat, etc.

Fertilizers

Fertilizers provide plant nutrients, commercially manufactured using chemicals. Fertilizers supply Nitrogen, Phosphorus, and Potassium (NPK). They are used for good vegetative growth (i.e., growth of leaves, branches, and flowers), giving rise to healthy plants. Fertilizers are one of the major components for obtaining higher yields, especially in expensive farming practices.

Fertilizers contain much higher amounts of nutrients in comparison to manures and are, therefore, used in very small quantities. A Complete fertilizer is one which contains all three critical elements or minerals, nitrogen, phosphorus, and potassium. These fertilizers may supply one or more nutrients. Chemically they may be inorganic compounds (e.g., ammonium sulphate) or organic compounds (e.g., urea).

On the basis of the availability of nutrients from them/fertilizers are divided into the following four groups:
1. Nitrogenous fertilizers: These fertilizers supply the macronutrient nitrogen.
Examples of nitrogenous fertilizers are:

• Urea, CO(NH₂)₂
• Ammonium sulphate, (NH₄)₂SO₄
• Calcium ammonium nitrate
• Sodium nitrate, NaNO₃
• Ammonium nitrate, NH₄NO₃

2. Phosphatic fertilizers: They are the source of the macronutrient phosphorus.
Examples of phosphatic fertilizers are:

• Single superphosphate
• Triple superphosphate
• Dicalcium phosphate

3. Potassic fertilizers: These fertilizers supply potassium which is one of the essential macronutrients of plants.
Examples of potassic fertilizers are:

• Muriate of potash or potassium chloride, KCl
• Potassium Sulphate, K₂SO₄
• Potassium nitrate, KNO₃

4. Complex fertilizers. When a fertilizer contains at least two or more nutrients (N, P₂O₅, and K₂O), it is called complex fertilizer.
Examples of complex fertilizers are:

• Nitro phosphate
• Ammonium phosphate
• Urea ammonium phosphate.

Fertilizers should be applied scientifically, in terms of proper dose, time, and pre-and post-application precautions for their complete utilisation. For example, sometimes due to excessive water, fertilizer gets, washed away and does not get fully absorbed by the plants. Fertilizers generally get washed off through’ irrigation, rainfall as drainage, and pollute rivers, lakes, and streams (causing toxicity, algal bloom, and eutrophication) and disturbing the ecosystem. The water of these water bodies becomes unfit for humans and judiciously.

Difference Between Manures and Fertilizers

Manure	Fertilizer
1. manure is a natural substance. It is obtained by the decomposition of animal wastes such as dung (gobar) of cattle and buffaloes and plant residues.	1. A fertilizer is a human-made substance. It is an inorganic salt or an organic compound.
2. manure contains small amounts of essential plant nutrients such as nitrogen, phosphorus, and potassium.	2. Fertilizers are very rich in plant nutrients such as nitrogen, phosphorus, and potassium.
3. A manure adds a great amount of organic matter in the form of humus in the soil.	3. A fertilizer does not add any humus to the soil.
4. Nutrients present in the manure are absorbed slowly by the crop plants since manure is not soluble in water. Nutrients exist locked inside the organic compounds of humus.	4. Being soluble in water, fertilizer is readily absorbed by the crop plants.
5. A manure is not nutrient specific and it tends to remove the general deficiency from the soil.	5. A fertilizer is nutrient specific. It can specifically provide nutrients such as nitrogen, phosphorus, and potassium to the soil according to the need.
6. A manure is voluminous and bulky so it is inconvenient to store, transport, handle and apply to the crop.	6. A fertilizer is compact and concentrated so it is easy to store, transport and apply to the crop.
7. manure is cheap and is prepared in rural homes or fields.	7. A fertilizer is costly and is prepared in factories.

5. Biofertilizers: Organisms that enrich the soil with nutrients are called biofertilizers. Biofertilizers are used for specific crop plants such as pulses, legumes, oil seeds, and rice. Biofertilizers are renewable and non-pollutant sources of plant nutrients such as nitrogen. They are not alternatives to chemical fertilizers but can play a supplementary role in supplying nitrogen to specific crops under specific soil conditions. Nitrogen-fixing microorganisms, i.e., non-symbiotic and symbiotic cyanobacteria and phosphate-solubilizing microorganisms, are the main type of biofertilizers that are being used in India. Recently, two biofertilizers, namely Rhizobium cultures and blue-green algae (such as Anabaena and Nostoc) have gained popularity amongst farmers cultivating pulses, legumes, oil seeds, and wet-land rice.

6. Mycorrhiza: Mycorrhiza is a symbiotic (mutualistic) association of certain fungi with roots of higher plants. Mycorrhiza increases water and nutrient uptake by plants and increases the growth, vigour, and yield of the plants.