Indian Bangalore method
This method of composting was developed at Bangalore in India in 1939 (FAO, 1980). It is recommended where night soil and refuse are used for preparing the compost. The method overcomes many of the disadvantages of the Indore method (below), such as the problem of heap protection from adverse weather, nutrient losses from high winds and strong sun, frequent turning requirements, and fly nuisance. However, the time required for the production of finished compost is much longer. The method is suitable for areas with scanty rainfall.
Trenches or pits about 1 m deep are dug; the breadth and length of the trenches can vary according to the availability of land and the type of material to be composted. Site selection is as per the Indore method. The trenches should have sloping walls and a floor with a 90-cm slope to prevent waterlogging.
Filling the pit
Organic residues and night soil are put in alternate layers. After filling, the pit is covered with a layer of refuse of 15-20 cm. The materials are allowed to remain in the pit without turning and watering for three months. During this period, the material settles owing to reduction in biomass volume. Additional night soil and refuse are placed on top in alternate layers and plastered or covered with mud or earth to prevent loss of moisture and breeding of flies. After the initial aerobic composting (about eight to ten days), the material undergoes anaerobic decomposition at a very slow rate. It takes about six to eight months to obtain the finished product.
Passive composting of manure piles
Passive composting involves stacking the materials in piles to decompose over a long time with little agitation and management (NRAES, 1992). The process has been used for composting animal wastes. However, the simple placing of manure in a pile does not satisfy the requirements for continuous aerobic composting. Without considerable bedding material, the moisture content of manure exceeds the level that enables an open porous structure to exist in the pile. Little if any air passes through it. Under these circumstances, the anaerobic micro-organisms dominate the degradation. All of the undesirable effects associated with anaerobic degradation occur.
Where a livestock management system relies on bedding to add to livestock comfort and cleanliness, the bedding becomes mixed with the manure and creates a drier, more porous mixture. This provides some structure and, depending on the amount of bedding, enables the mixture to be stacked in true piles. The bedding also tends to raise the C:N ratio of the manure.
A mixture of manure and bedding requires a considerable proportion of bedding to provide the porosity necessary for composting. At least equal volumes of bedding and manure are required. Where the amount of bedding is insufficient to provide a porous mix, additional dry amendments must be provided by either increasing the bedding used in the barn or adding amendments when piles are formed. Manure from horse stables or bedded manure packs (animal bedding and manure mixture) can often compost in piles alone, whereas non-bedded manure from dairy, swine and many poultry barns needs drying or additional amendments.
The pile must be small enough to allow passive air movement, generally less than 2 m high and 4 m wide. This passive method of composting is essentially wind-row composting but with a much less frequent turning schedule. It is a common method for composting leaves. It demands minimal labour and equipment. Passive composting is slow because of its low aeration rate, and the potential for odour problems is greater.
Indian Coimbatore method
This method (Manickam, 1967) involves digging a pit (360 cm long × 180 cm wide × 90 cm deep) in a shaded area (length can vary according to the volume of waste materials available). Farm wastes such as straw, vegetable refuse, weeds and leaves are spread to a thickness of 15-20 cm. Wet animal dung is spread over this layer to a thickness of 5 cm. Water is sprinkled to moisten the material (50-60 percent of mass). This procedure is repeated until the whole mass reaches a height of 60 cm above ground. It is then plastered with mud, and anaerobic decomposition commences. In four weeks, the mass becomes reduced and the heap flattens. The mud plaster is removed and the entire mass is turned. Aerobic decomposition commences in at this stage. Water is sprinkled to keep the material moist. The compost is ready for use after four months.
Indian Indorepit method
An important advance in the practice of composting was made at Indore in India by Howard in the mid-1920s. The traditional procedure was systematized into a method of composting now known as the Indore method (FAO, 1980).
The raw materials used are mixed plant residues, animal dung and urine, earth, wood ash and water. All organic material wastes available on a farm, such as weeds, stalks, stems, fallen leaves, prunings, chaff and fodder leftovers, are collected and stacked in a pile. Hard woody material such as cotton and pigeon-pea stalks and stubble are first spread on the farm road and crushed under vehicles such as tractors or bullock carts before being piled. Such hard materials should not exceed 10 percent of the total plant residues. Green materials, which are soft and succulent, are allowed to wilt for two to three days in order to remove excess moisture before stacking; they tend to pack closely when stacked in the fresh state. The mixture of different kinds of organic material residues ensures a more efficient decomposition. While stacking, each type of material is spread in layers about 15 cm thick until the heap is about 1.5 m high. The heap is then cut into vertical slices and about 20-25 kg are put under the feet of cattle in the shed as bedding for the night. The next morning, the bedding, along with the dung and urine and urine-earth, is taken to the pits where the composting is to be done.
Pit site and size
The site of the compost pit should be at a level high enough to prevent rainwater from entering in the monsoon season; it should be near the cattle shed and a water source. A temporary shed may be constructed over it to protect the compost from heavy rainfall. The pit should be about 1 m deep, 1.5-2 m wide, and of a suitable length.
Filling the pit
The material brought from the cattle shed is spread in the pit in even layers of 10-15 cm. A slurry made from 4.5 kg of dung, 3.5 kg of urine-earth and 4.5 kg of inoculum from a 15-day-old composting pit is spread on each layer. Sufficient water is sprinkled over the material in the pit to wet it. The pit is filled in this way, layer by layer, and it should not take longer than one week to fill. Care should be taken to avoid compacting the material in any way.
The material is turned three times while in the pit during the whole period of composting: the first time 15 days after filling the pit; the second after another 15 days; and the third after another month. At each turning, the material is mixed thoroughly and moistened with water.
Indian Indore heap method
Heap site and size
During rainy seasons or in regions with heavy rainfall, the compost may be prepared in heaps above ground and protected by a shed. The pile is about 2 m wide at the base, 1.5 m high and 2 m long. The sides taper so that the top is about 0.5 m narrower than the base. A small bund is sometimes built around the pile to protect it from wind, which tends to dry the heap.
Forming the heap
The heap is usually started with a 20 cm layer of carbonaceous material such as leaves, hay, straw, sawdust, wood chips and chopped corn stalks. This is covered with 10 cm of nitrogenous material such as fresh grass, weeds or garden plant residues, fresh or dry manure or digested sewage sludge. The pattern of 20 cm of carbonaceous material and 10 cm of nitrogenous material is repeated until the pile is 1.5 m high and the material is normally wetted until it feels damp but not soggy. The pile is sometimes covered with soil or hay to retain heat and it is turned at intervals of 6 and 12 weeks. In the Republic of Korea, the heaps are covered with thin plastic sheets to retain heat and prevent insect breeding.
Where materials are in short supply, the alternate layers can be added as they become available. Moreover, all the materials can be mixed together in the pile provided that the proper proportions are maintained. Shredding the material speeds up decomposition considerably. Most materials can be shredded by running a rotary mower over them several times. Where sufficient nitrogenous material is not available, a green manure or leguminous crop such as sun hemp is grown on the fermenting heap by sowing seeds after the first turning. The green matter is then turned in at the time of the second mixing. The process takes about four months to complete.
Tipping organic wastes into a pit; they are spread out into an even layer
Chinese rural composting - pit method
Under this method, the composting is generally carried out in a corner of a field in a circular or rectangular pit (FAO, 1980). Rice straw, animal dung (usually pig), aquatic weeds and green manure crops are used. Silt pumped from river beds is often mixed with the crop residues. The pits are filled layer by layer, each layer being 15 cm thick. Usually, the first layer is a green manure crop or water hyacinth, the second layer is a straw mixture (Plate 1) and the third layer is animal dung. These layers are alternated until the pit is full, when a top layer of mud is added. A water layer of about 4 cm deep is maintained on the surface to create anaerobic conditions, which helps to reduce N losses. The approximate quantities of the different residues in terms of tonnes per pit are: river silt 7.5, rice straw 0.15, animal dung 1.0, aquatic plants or green manure 0.75, and superphosphate 0.02. In total, there are three turnings. The first turning is given one month after filling the pit and, at this time, the superphosphate is added and mixed in thoroughly. Water is added as necessary. The second turning is done after another month and the third two weeks later. The material is allowed to decompose for three months and produces about 8 tonnes of compost per pit.
Chinese rural composting - high temperature method
This form of compost is prepared mainly from night soil, urine, sewage, animal dung, and chopped plant residues at a ratio of 1:4. The materials are heaped in alternate layers starting with chopped plant stalks and followed by human and animal wastes; water is added to an optimal amount.
At the time of making the heap, a number of bamboo poles are inserted for aeration purposes. Once the heap formation is complete, it is sealed with 3 cm of mud plaster. The bamboo poles are withdrawn on the second day of composting, leaving the holes to provide aeration. Within four to five days, the temperature rises to 60-70 °C and the holes are then sealed. The first turning is usually done after two weeks and the moisture is made up with water or animal or human excreta; the turned heap is again sealed with mud. The compost is ready for use within two months.
In some locations, a modified method of high temperature composting is used. The raw materials, crop stalks (30 percent), night soil (30 percent) and silt (30 percent), are mixed with superphosphate at the rate of 20 kg of superphosphate per tonne of organic material. The compost heaps have aerating holes made by inserting bundles of maize stalks instead of bamboo poles.
Ecuador on-farm composting
Under this method, the raw materials utilized for compost making are:
animal manure: from cows, pigs, poultry, horses, donkeys, ducks, etc.;
crop residues and weeds: maize, bean, broad bean, groundnut, coffee and weeds;
agro-industrial wastes, ash and phosphate rock;
topsoil from the forest or from an uncultivated or sparingly cultivated area;
The raw materials are put in layers in the following sequence (Figure 2):
a layer of crop residues (20 cm);
a layer of topsoil (2 cm);
a layer of manure (5-10 cm).
Ash or phosphate rock (50 g/m2) is then spread on the surface, and freshwater is sprinkled on the material.
Ecuador heap composting
The above steps are repeated until a height of about 1-1.2 m is reached. It is recommended to begin the heap by constructing a lattice of old branches, and to place two or three woodcuttings vertically along the lattice in order to facilitate ventilation. The heap should be 2 m × 1-1.2 m × 1-1.2 m. Once a week water should be added to the heap. However, too much water could lead to the leaching of nutrients. After three weeks, the heap must be mixed to ensure that all materials reach the centre. During the process, the temperature rises to 60-70 °C, and most weed seeds and pathogens are killed. While it may take about two to three months to prepare the compost in a warm climate, in cold regions it could take five to six months.
Berkley rapid composting method - shredding and frequent turning
This method (Raabe, 2001) corrects some of the problems associated with the earlier methods of composting. The process can produce compost in two to three weeks. Several factors are essential to the rapid composting method:
Material composts best when it is 1.25-3.75 cm in size. Soft, succulent tissues do not need chopping into very small pieces because they decompose rapidly. The harder or woodier the tissues, the smaller they need to be in order to decompose rapidly. Woody material should be passed through a grinder. Chopping material with a sharp shovel is effective. When pruning plants, the material should be cut into small pieces using the pruning shears. This requires a little effort but the results are worth it
For the composting process to work most effectively, the material to be composted should have a C:N ratio of 30:1. Mixing equal volumes of green plant material with equal volumes of naturally dry plant material yields such a ratio. The green material can be grass clippings, old flowers, green prunings, weeds, fresh garbage and fruit and vegetable wastes. The dried material can be fallen leaves, dried grass, straw and woody materials from prunings.
Materials that should not be added to a composting pile include: soil, ashes from a stove or fireplace, and manure from carnivorous animals. Manures from herbivorous animals such as rabbits, goats, cattle, horses, elephants and fowl can be used. Once a pile has been started, nothing should be added. This is because it takes a certain length of time for the material to break down and anything added has to start at the beginning, thus lengthening the decomposition time for the whole pile. Excess material should be as dry as possible during storage until a new pile is started. Moist stored materials start to decompose. If this occurs, they will not be effective in the compost pile. Nothing needs to be added to the organic materials to make them decompose. The micro-organisms active in the decomposition process are ubiquitous where plant materials are found and develop rapidly in any compost pile.
Composting works best where the moisture content of materials in the pile is about 50 percent. Too much moisture creates a soggy mass, and decomposition will then be slow and the pile will smell. Where the organic material is too dry, decomposition is either very slow or does not occur at all.
Heat, which is very important in rapid composting, is supplied by the respiration of the micro-organisms as they break down the organic materials. To prevent heat loss and to build up the amount of heat necessary, a minimum volume of material is essential. The pile should be at least 90 cm × 90 cm × 90 cm in size. Where the dimensions are less than 80 cm, the rapid process will not occur. Heat retention is better in bins than in open piles, so rapid composting is more effective where bins are used. In addition, the use of bins is much neater. High temperatures favour the micro-organisms that are the most rapid decomposers; these micro-organisms function at about 71 °C and a good pile maintains itself at about that temperature.
The compost pile needs to be turned to prevent it from overheating. If the temperature in the pile rises much above 71 °C, the micro-organisms will be killed, the pile will cool, and the whole process will have to start again from the beginning. Turning the pile prevents overheating and aerates the pile, both necessary conditions for keeping the most active decomposers functioning. The pile should be turned in a manner that the material is moved from the outside to the centre. In this way, all the material reaches optimal temperatures at various times. Owing to heat loss around the margins, only the central portion of the pile is at the optimal temperature. Because of the need for turning, it is desirable to have two bins so that the material can be turned from one into another. Bins with removable slats in the front facilitate the turning process. Bins with covers retain the heat better than those without. Once the decomposition process starts, the pile becomes smaller and, because the bin is no longer full, some heat will be lost at the top. This can be prevented by using a piece of polyethylene plastic slightly larger than the top area of the bin. After the compost has been turned, the plastic is placed directly on the top of the compost and is tucked in around the edges. If the material in the pile is turned every day, it will take two weeks or a little longer to compost. If turned every other day, it will take about three weeks. The longer the interval between turning, the longer it will take for the composting to finish.
If the procedure is followed properly, a pile heats to a high temperature within 24-48 hours. If it does not do so, this means that the pile is too wet or too dry or that there is not enough green material (or N) present. If too wet, the material should be spread out to dry. If too dry, moisture should be added. If neither of these, then the N is low (a high C:N ratio), and this can be corrected by adding materials high in N (such as ammonium sulphate, grass clippings, fresh chicken manure or urine diluted 1 to 5).
Where the C:N ratio is less than 30:1, the organic matter decomposes very rapidly but there is a loss of N. This is given off as ammonia, and where this odour is present in or around a composting pile, it means that valuable N is being lost in the air. This can be counteracted by adding sawdust to that part of the pile where there is an ammonia odour (sawdust is very high in C and low in N). Some covering for the pile may be necessary in order to keep the composting materials from becoming too wet during the rainy season.
The rapid decomposition can be detected by a pleasant odour, by the heat produced (visible in the form of water vapour given off during the turning of the pile), by the growth of white fungi on the decomposing organic material, by a reduction of volume, and by the materials changing colour to dark brown. As composting nears completion, the temperature drops and, finally, little or no heat is produced. The compost is then ready to use. If the material was not chopped into small pieces during the preparation phase, screening the material through 2.5-cm-mesh chicken wire will hold back the large pieces. These can be added to the next pile and eventually they will decompose.
North Dakota State University hot composting - use of mineral nitrogen activator
Under this method (Smith, 1995), compost piles with a height of 1.8 m are raised. The maximum size of the organic matter pieces should be 15-23 cm long. Where bins are constructed, dimensions of about 152 × 152 × 183 cm yield 4.3 m3 of compost in four to six weeks.
To keep the aerobic bacteria population high and active, proportionate amounts of nitrogenous fertilizer should be added (0.12 kg of fertilizer per 0.0283 m3 of dry matter) and four or five holes punched into the centre of the pile. This is best done in phases or stages as the compost pile is building up. For example, for 4.3 m3 of dry matter, where the pile is built up over a period of three stages at 60, 120 and 180 cm, 5.7 kg of N fertilizer should be added at each step. The total should be about 17-18 kg of fertilizer for the entire pile.
In this high temperature, bacterially active system, it is best to turn the composting material every three or four days. Once activated, the temperature range should be 49-71 °C. The decomposition happens more rapidly in summer (as short as three to four weeks) and take more time in spring and autumn. No measurable activity occurs during typical winters in North Dakota, the United States of America. Once the compost is no longer hot and is an odour-free, crumbling material, it is ready for use.
Composting organic materials with high lignin content - lime treatment
By adding organic wastes such as sawdust, wood shavings, coir pith, pine needles, and dry fallen leaves, while preparing organic waste mixtures for composting, one can ensure that the compost produced contains sufficient and long-lasting humus. However, gardeners often find that where they use lignin-rich plant materials, the compost does not ripen rapidly. A technique for making good compost from hard plant materials involves mixing lime in a ratio of 5 kg per 1 000 kg of waste material. Lime can be applied as dry powder or after mixing with a sufficient quantity of water. Treatment with lime enhances the process of decomposition of hard materials. Liming can enhance the humification process in plant residues by enhancing microbial population and activity and by weakening lignin structure. It also improves the humus quality by changing the ratio of humic to fulvic acids and decreases the amount of bitumen, which interferes with the decomposition process. Instead of lime, powdered phosphate rock can be used in a ratio of 20 kg per 1 000 kg of organic waste. Phosphate rock contains a lot of lime. The phosphates and micronutrients contained in phosphate rock make composts rich in plant nutrients.
EM-based quick composting
Effective micro-organisms (EM) consist of common and food-grade aerobic and anaerobic micro-organisms: photosynthetic bacteria, lactobacillus, streptomyces, actinomycetes, yeast, etc. The strains of the micro-organisms are commonly available from microbe banks or from the environment. There are no genetically engineered strains that are in use. Since 1999, seven small-scale organic fertilizer units have been using the EM-based quick production process in Myanmar (FAO, 2002). They are owned and operated by women's income generation groups. A unit consists of nine pits measuring about 180 cm (length) × 120 cm (width) × 90 cm (depth), enclosed by low walls and covered with a roof (Plate 2).
The raw materials for organic fertilizer production are:
cow dung - 2 portions;
rice husk - 1 portion;
rice husk-charcoal - 1 portion;
rice bran, milled - 1 portion;
accelerator - 33 litres of EM solution or Trichoderma solution per pit.
EM-based quick composting in Myanmar
Preparation of EM solution (accelerator)
One litre of 'instant solution' is made by mixing 10 ml of EM, 40 ml of molasses and 950 ml of water and leaving it for five to seven days, depending on temperature. The solution is then added to 1 litre of molasses and 98 litres of water to obtain 100 litres of ready-to-use EM solution. This amount is enough for three pits. The EM solution functioning as accelerator reduces the composting period from three months to one month.
All the ingredients are mixed together, except accelerator. A 15 cm layer of mixture is spread in the pit and accelerator is sprinkled on it. This procedure is repeated until the pit is full. The pit is covered with a plastic sheet (Plate 3). Two or three weeks later, the whole pit is mixed in order to boost aerobic decomposition. The compost is ready to use a couple of weeks later. A pit produces 900 kg of final product per batch. The product is usually packed in 30-kg plastic bags. Assuming that it takes 30 days on average to produce a batch and that only eight pits may be used for technical reasons, the annual potential production capacity is 86.4 tonnes (0.9 tonnes × 8 pits × 12 months).
Within the framework of the FAO Technical Cooperation Programme project on promotion of organic fertilizers in Lao PDR (TCP/LAO/2901), a simple EM-based quick composting method, as detailed below, is promoted.
The raw materials for compost production are:
Straw is stacked in layers of 20 cm height, 1 m width, and 5 m length to form a pile. A unit pile is about 5 m (length) × 1 m (width) × 1 m (height) in size. The pile is sprinkled with water (Plate 4) for adequate moisture content, followed by addition of a manure layer 5 cm high, and the sprinkling of a few handfuls of urea (100-200 g). EM solution, prepared in the same way as described in the Myanmar example, is sprinkled to accelerate aerobic decomposition.
Compost pile in preparation
[Singvilay (TCP/LAO/2901), Lao PDR]
The pile is covered with a plastic sheet after attaining the desired height
[Singvilay (TCP/LAO/2901), Lao PDR]
The pile is being turned
[Singvilay (TCP/LAO/2901), Lao PDR]
This procedure is repeated until the pile is about 1 m high and then it is covered with a plastic sheet (Plate 5). The pile is turned after two weeks (Plate 6) and then again after another week. Normally, the compost is ready two weeks later when the heap has cooled down and the height of the pile has fallen to about 70 cm.
The IBS rapid composting technology (Virginia, 1997) involves inoculating the plant substrates used for composting with cultures of Trichoderma harzianum, a cellulose decomposer fungus. The fungus, grown in a medium of sawdust mixed with the leaves of a leguminous tree called ipil ipil (Leucaena leucocephala), is termed compost fungus activator (CFA). The technology is a development of the wind-row type of composting. Using this procedure, the composting time ranges from 21 to 45 days depending on the plant substrates used.
The procedure consists of two parts: the production of the CFA, and the composting process.
Preparation of substrates
Substrates such as rice straw, weeds and grasses should be chopped. Chopping helps speed up decomposition by increasing the surface area available for microbial action and providing better aeration. Where large quantities of substrates are to be used (i.e. several tonnes), a forage cutter/chopper is needed. Chopping can be dispensed with where the compost is not needed in the near future.
Adjustment of moisture content
Substrates should be moistened with water. Plant substrates can be soaked overnight in a pond, which reduces the need for water. Where a large volume of substrates are to be composted, a sprinkler is more convenient.
The compost mixture
Carbonaceous substrates should be mixed with nitrogenous ones at a ratio of 4:1 or less, but never lower than 1:1 (on a dry weight basis). Some possible combinations are:
3 parts rice straw to 1 part ipil ipil;
4 parts rice straw to 1 part chicken manure;
4 parts grasses to 1 part legume materials + 1 part manure;
4 parts grasses to 1 part Chromolaena odorata (a common broad-leaf weed) or Mikania cordata (a herbaceous climbing plant) + 1 part animal manure; it is important to use grasses and weeds that do not have flowers or seeds.
The substrates should be piled loosely in a compost pen to provide better aeration within the heap. The material should not be too compact and no heavy weights should be placed on top. Compost heaps should be located in shady areas, e.g. under large trees. The platform should be raised about 30 cm from the ground in order to provide adequate aeration at the bottom. Alternatively, aeration can be provided by placing perforated bamboo trunks horizontally and vertically at regular intervals.
The CFA is broadcast onto the substrates during piling. The amount of activator used is usually 1 percent of the total weight of the substrates (i.e. about 1 kg compost activator per 100 kg substrate). Decomposition is faster where the activator is mixed thoroughly with the substrate. A larger amount of activator can be used should faster decomposition be desired.
The heap should be covered over completely. This maintains the heat of decomposition, and minimizes water evaporation and ammonia volatilization. White plastic sheets, or plastic sacks with their seams opened and sewn together, can serve as a cover. The compost heap usually heats up in 24-48 hours.
The temperature should be maintained at 50 °C or higher, and the heap should be turned every five to seven days for the first two weeks, and thereafter once every two weeks. After the first week, the volume of the pile should be reduced by one-third. After two weeks, the volume of the pile should be reduced to one-half the original volume.
The mature compost should be removed from the pen and dried in the sun for two days. It should then be put into sacks and stored in a shaded area. Decomposition should be allowed to continue until the substrate is finely fragmented, so that the finished product has a powdery texture. When decomposition is complete, the compost should be sun-dried again until the moisture content is 10-20 percent.
Where mature compost is needed at once, it should be sun-dried for one day as soon as its temperature drops to 30 °C. Drying removes excess moisture and makes the compost much easier to handle. Although the compost still retains some fibres, it can be applied immediately as fertilizer.
In the large-scale commercial production of compost, the following operations need to be mechanized (other steps remaining the same):
Chopping of substrates - a forage cutter/chopper could be used.
Mixing/turning - where there are several tonnes of substrate, a pay loader facilitates mixing of substrates and turning of heaps.
A hammer mill should be used to break up large lumps of mature compost before drying.
During rainy months, it is more economical to dry compost mechanically rather than in the sun.
Composting organic materials with high lignin content - coir pith
Coir pith is a waste from the coir industry (TNAU, 1999). This is a major industry that produces coconuts on a large scale. During the process of separating fibre from the coconut husk, a large volume of pith is collected. The pith, containing about 30 percent lignin and 26 percent cellulose, does not degrade rapidly, posing a major disposal problem. However, it can be composted by using the fungus Pleurotus sp. and urea. To compost 1 tonne of coir pith, the materials required are: five spawn bottles (250 g) of Pleurotus sp. and 5 kg of urea
The first step in the compost preparation is to select an elevated shaded place, or to erect a thatched shed. The surface is then levelled and an area 500 cm × 300 cm is marked out. To start with, about 100 kg of coir pith is spread. About 50 g of Pleurotus spawn is spread over this layer. About 100 kg of coir pith is spread on that. On this layer, 1 kg of urea is spread uniformly. The process is repeated until all the pith (1 tonne) is utilized. Water is sprinkled repeatedly so as to maintain the moisture optimum of 50 percent. Well-decomposed black compost is ready in about a month. The C:N ratio falls to about 24:1 and the N content rises from 0.26 to 1.06 percent.
This method has been developed for composting weeds such as parthenium, water hyacinth (Eichornia crassipes), cyperus (Cyperus rotundus) and cynodon (Cynodon dactylon). The materials required are: 250 g of Trichoderma viride and Pleurotus sajor-caju consortia, and 5 kg of urea. An elevated shaded place is selected, or a thatched shed is erected. An area of 500 cm × 150 cm is marked out. The material to be composted is cut to 10-15 cm in size. About 100 kg of cut material is spread over the marked area. About 50 g of microbial consortia is sprinkled over this layer. About 100 kg of weeds are spread on this layer. One kilogram of urea is sprinkled uniformly over the layer. This process is repeated until the level rises to 1 m. Water is sprinkled as necessary to maintain a moisture level of 50-60 percent. Thereafter, the surface of the heap is covered with a thin layer of soil. The pile requires a thorough turning on the twenty-first day. The compost is ready in about 40 days.
Farm compost is poor in P content (0.4-0.8 percent). Addition of P makes the compost more balanced, and supplies nutrient to micro-organisms for their multiplication and faster decomposition. The addition of P also reduces N losses. Compost can be enriched by:
Application of superphosphate, bonemeal or phosphate rock (Ramasami, 1975): 1 kg of superphosphate or bonemeal is applied over each layer of animal dung. Low-grade phosphate rock can also be used for this purpose.
Use of animal bones: these can be broken into small pieces, boiled with wood ash leachate or lime water and drained, and the residue applied to the pits. This procedure of boiling bones facilitates their disintegration. Even the addition of raw bones, broken into small pieces and added to the pit, improves the nutrient value of compost significantly.
Wood ash waste can also be added to increase the K content of compost.
Addition of N-fixing and P-solubilizing cultures (IARI, 1989): The quality of compost can be further improved by the secondary inoculation of Azotobacter, Azospirillum lipoferum, and Azospirillum brasilence (N-fixers); and Bacillus megaterium or Pseudomonas sp. (P solubilizers). These organisms, in the form of culture broth or water suspension of biofertilizer products, can be sprinkled when the decomposing material is turned after one month. By this time, the temperature of the compost has also stabilized at about 35 °C. As a result of this inoculation, the N content of straw compost can be increased by up to 2 percent. In addition to improving N content and the availability of other plant nutrients, these additions help to reduce the composting time considerably.