Soil Fertility Management: Chemical, Organic, and Biofertilizer Methods
Understanding Fertilizers and Soil Nutrients
A fertilizer is any natural or synthetic substance (solid, liquid, or gaseous) containing one or more plant nutrients (other than lime) that is applied to the soil or leaves to supply nutrients essential for the growth of plants. The following four main types of fertilizers are recognized:
- Chemical Fertilizers
- Organic Fertilizers or Manures
- Biofertilizers
- Plant Growth Promoting Rhizobacteria (PGPR)
Chemical Fertilizers
Chemical fertilizers are manures or mixtures of different chemicals used for improving soil fertility. Chemical fertilizers are further categorized into three types:
- Single Nutrient Fertilizers: These fertilizers contain only one nutrient element, most often nitrogen (N) or phosphorus (P). Examples include Urea (CO(NH2)2, carbamide) and calcium ammonium nitrate (Ca(NO3)2 NH4NO3, 10H2O).
- Binary Fertilizers: These fertilizers contain two components or nutrient elements. Examples include NP fertilizers such as monoammonium phosphate (MAP) and diammonium phosphate (DAP).
- Multinutrient or Complex Fertilizers: These are the most common type of fertilizer used today. They consist of more than two nutrient components or elements. An example is NPK fertilizer, which contains nitrogen, phosphorus, and potassium.
Disadvantages of Chemical Fertilizers
- They upset the pH and destroy the friability (crumbly texture) of the soil.
- They increase the susceptibility of crops to pests and diseases.
- They leach out into the soil and pollute water resources.
- Chemical fertilizers are often economically costly.
Vermicompost Production Methodology
Vermicomposting is an aerobic, bio-oxidation, non-thermophilic process of organic waste decomposition that depends upon earthworms to fragment, mix, and promote microbial activity. The basic requirements during the process of vermicomposting are as follows:
1. Selection of Suitable Earthworm Species
Only surface-dwelling earthworms should be used for this process. Earthworms that live below the soil surface are not suitable for vermicompost production. Promising worms used include the African earthworm (Eudrilus eugeniae), Red worms (Eisenia foetida), and the composting worm (Peronyx excavatus). All three worms can be mixed together. The African worm (Eudrilus eugeniae) is often preferred because it yields higher production of vermicompost and younger worms in a shorter period of time.
2. Selection of Site for Vermicompost Production
Vermicompost can be produced in any place with shade, high humidity, and cool temperatures. Vacant cattle sheds or poultry sheds can also be used. A thatched roof should be provided to protect the process from direct sunlight and rain. The waste heaped for vermicompost production should be covered with moist gunny bags.
3. Containers for Vermicompost Production
A cement tub may be constructed to a height of 2.5 feet and a breadth of 3 feet. The length can be fixed depending upon the size of the room. The bottom of the tub should be sloped to drain excess water from the vermicompost unit.
4. Selection of Waste Materials
Suitable materials for vermicompost production include cattle dung (except pig, poultry, and goat), farm wastes, crop residues, vegetable market waste, flower market waste, agro-industrial waste, fruit market waste, and all other biodegradable waste. The cattle dung should be dried in open sunlight before use. All other waste should be predigested with cow dung for twenty days before being put into the vermibed for composting.
5. Putting the Waste in the Container
The predigested waste material should be mixed with 30% cattle dung either by weight or volume. The mixed waste is placed into the tub or container up to the top. The moisture level should be maintained at 60%. The selected earthworms are placed uniformly over this material. For a unit measuring one-meter length, one-meter breadth, and 0.5-meter height, 1 kg of worms (approximately 1,000 individuals) is required. It is not necessary to put the earthworms inside the waste; they will move inside on their own.
6. Watering the Vermibed
Daily watering is not required for the vermibed, but 60% moisture must be maintained throughout the period. If needed, water should be sprinkled over the bed rather than poured. Watering should be stopped before the harvest of vermicompost.
7. Harvesting of Vermicompost
The compost is ready when the material is moderately loose, powdery, and dark brown. It will be black, granular, lightweight, and humus-rich. The compost should be ready, as indicated by the presence of earthworm casings (vermicompost) on the top of the bed, in 60 to 90 days (depending upon the size of the pit). Vermicompost can now be harvested from the bin or pit.
Methods for Separating Worms During Harvest
- The separation of the worms from the compost can be facilitated by preventing watering two to three days before emptying the beds. This will force about 80 percent of the worms to the bottom of the bed.
- The worms can also be separated by using sieves or meshes. The earthworms and the thicker leftover material on the top of the sieve go back into the bin, and the process starts again.
- The harvested material should be placed in a heap. The worms will move down to the cool base of the heap.
- In the two- or four-pit system, watering should be stopped in the first chamber so that worms will automatically move to another chamber where the required environment is maintained in a cyclic manner, allowing continuous harvesting in cycles.
The smell of the finished compost should be earth-like. Any bad odor indicates incomplete fermentation and that bacterial processes are still ongoing. A musty smell indicates the presence of mold or overheating, which leads to nitrogen loss. If this happens, aerate the heap, add more fibrous material, and keep the heap drier. The compost is then sieved before being packed.
Green Manures and Manuring Practices
Green manures are plants that are grown to provide soil cover and to improve the physical, chemical, and biological characteristics of the soil. These crops may be sown independently or in association with other crops. Green manures, also referred to as fertility-building crops, may be broadly defined as crops grown for the benefit of the soil.
The process of raising green manure is known as Green Manuring. It is the process of turning green plants into the soil, either by raising them in the same field or by incorporating plants grown elsewhere at the green stage (before flowering) into the soil.
Green manuring, defined by Pieters as ‘the practice of enriching the soil by turning under fresh plant material either in situ or brought from a distance,’ is a widely used practice in organic farming to maintain soil organic matter. Green manure is also known as green compost and is low-cost manure, often called ‘the poor farmer’s manure.’
Many organic farmers prefer to use this method as it is a natural way of gardening. Gardeners who are serious about being sustainable, organic, and biodynamic will devote a good percentage of their garden to the green composting method. Some large-scale organic farmers even use this technique to enrich their soil without the expense of buying nutrients or the risk of adding toxins to their soil.
Composting Methods and Waste Management
Comparison of Aerobic and Anaerobic Composting
| Aerobic Composting | Anaerobic Composting |
|---|---|
| It is above-ground composting and works in the presence of oxygen. | It is underground composting and works without oxygen. |
| Aerobic decomposers work faster and more efficiently than their anaerobic counterparts as long as plenty of air is available. However, the decomposition process slows as the supply of oxygen depletes. | Anaerobic organisms work at slower rates than their aerobic counterparts, and it is impossible to monitor their progress without digging into the hole and poking around. |
| Aerobic organisms do not exude smelly gas as a byproduct of their exertions. | Anaerobic organisms exude smelly gas as a byproduct of their exertions. |
| Weed seeds and plant pathogens are destroyed because of the hot conditions. | Weed seeds and plant pathogens are not destroyed because of the colder conditions. |
Defining Waste
Wastes are materials that are not prime products (products produced for the market) for which the initial user has no further use in terms of their own purposes of production, transformation, or consumption, and of which they want to dispose. Waste is directly linked to human development, both technologically and socially. The compositions of different wastes have varied over time and location, with industrial development and innovation being directly linked to waste materials (e.g., plastics and nuclear technology). Some components of waste have economic value and can be recycled once correctly recovered.
Anaerobic Digestion
Anaerobic digestion is the digestion of organic solid waste in the absence of free oxygen and can be broadly grouped into two major steps:
- Acid Fermentation: In this process, acidogenic bacteria hydrolyze the complex polymeric substrates into organic acids, alcohols, sugars, H2, and CO2.
- Methane Fermentation: In methane fermentation, long-chain fatty acids and alcohols are converted to short-chain fatty acids and CO2. Hydrogenation of CO2 releases methane in addition to acetate-digested methane which gets released.
Composting
Composting is the natural process of rotting or decomposition of organic matter by microorganisms under controlled conditions. Raw organic materials such as crop residues, animal wastes, food garbage, some municipal wastes, and suitable industrial wastes, enhance their suitability for application to the soil as a fertilizing resource after composting. Compost is a rich source of organic matter.
Azolla and Anabaena: A Symbiotic Relationship
Azolla ferns have filaments of Anabaena living within ovoid cavities inside the leaves. The relationship appears to be mutually beneficial, and this fern and its algal partner provide an important contribution toward the production of rice for a hungry world.
The Azolla leaf consists of a thick, greenish (or reddish) dorsal (upper) lobe and a thinner, translucent ventral (lower) lobe immersed in the water. The upper lobe has an ovoid central cavity, the living quarters for filaments of Anabaena. The easiest way to observe Anabaena is to remove a dorsal leaf lobe and place it on a clean slide with a drop of water. Apply a cover slip with sufficient pressure to mash the leaf fragment.
Anabaena are heterocyst-forming, photoautotrophic cyanobacteria that perform oxygenic photosynthesis. Anabaena grow in long filaments of vegetative cells. The filament consists of a string of beaded cells. Filaments occur singly within a sheath, and sheaths are always hyaline and watery gelatinous. About one cell out of every ten will differentiate into a heterocyst during times of low environmental nitrogen. Heterocysts then supply neighboring cells with fixed nitrogen in return for the products of photosynthesis, which they can no longer perform. This separation of functions is essential because the nitrogen-fixing enzyme in heterocysts, nitrogenase, is unstable in the presence of oxygen. Due to the necessity of keeping nitrogenase isolated from oxygen, heterocysts have developed elements to maintain a low level of oxygen within.