In this article we will discuss about:- 1. Organic Composts 2. Composting 3. Importance 4. Method of Spreading 5. Classification 6. Method of Operation.
Compost is a mixture of decaying organic matter, as from leaves and manure, used to improve soil structure and provide nutrients. It is a composition; a mixture to fertilize with a mixture of decaying organic matter or to convert (vegetable matter) to compost. Compost is the dark brown crumbly material that is produced when a collection of plant and animal material is decomposed into fine organic matter and humus.
It is prepared from urine, dried blood, pig manure, poultry manure, comfrey, lawn trimmings, kitchen compost, farmyard manure, seaweed, garden compost, coffee grounds, horse manure, weeds, bracken, straw, woody pruning, bark, newspaper, cardboard, sawdust, etc.
Once the compost has been mixed into the soil it will undergo the process of mineralization in which the humus releases minerals into the soil, making them available to the plants.
The production of compost is the heart of the organic method. Dying and decaying matter, whether the falling leaves of the forest or the decaying bodies of more complex life forms, is constantly being used as the raw material of new life. In nature, the forest floor is the workshop for a continuous compost production operation.
In agriculture fields, this normal cycle is interrupted by taking out some of the organic material produced. In setting up a compost-making operation, we are restoring the cycle and returning to the soil the humus, which is the single most important element in its fertility. The process of compost or life renewal is achieved by a remarkably complex interaction of billions of microscopic life forms with biological materials.
Composting is a biological decomposition process that converts organic matter to a stable, humus-like product under controlled conditions. During the composting process, microorganisms utilize the decomposable microbial substrates present in the organic compost both as an energy source and for conversion to microbial substances.
The composting process of simply a means of converting raw organic compost, a potential source of odor and public health problems, into a safe product called humus. By definition, composting is an alternative system for solving some of the compost handling problems existing on today’s farms.
It is a natural process, which occurs in nature in which organic matter is decomposed by microorganisms forming a humus-like substance. The process itself is not new. It has been in practice for many centuries by farmers who have stacked animal manure into piles or gardeners who have placed garbage, leaves, grass cuttings, etc., into pits.
Despite its wide usage, no advances were made in the treatment process until 1925 when Sir Albert Howard, a British agronomist stationed in India, developed a systemized process for composting. The improved process was labeled the Indore Method after the stage in central India where it was conceived and tested.
The method described by Howard (1935) involves the formation of a layered pile about 1.5 m high using garbage, animal composts, sewage sludge, straw, and leaves. Initially the process was anaerobic and required 6 months for completion to occur. The process was later modified by turning the pile over twice, which reduced the composting time to 3 months.
Importance of Composting:
A great deal of organic compost from the kitchen and farm can be recycled and given back to the soil in the form of compost.
When compost is added to the soil the level of organic matter increased, which is beneficial in many ways:
(1) The finished product obtained from composting may have some fertilizer value but it should be strongly emphasized that compose is an excellent soil conditioning agent.
(2) Incorporating compost into the soil increases the organic content and improves the texture, the permeability, and the water-holding capacity of that soil.
(3) An improvement in humus content, hygroscopic moisture, water retention capacity, and absorption capacity when organic matter is added to the soil.
(4) Compost can be used for improving the fertility of marginal and arable land and also for restoration of land that has been severely eroded or strip mined.
(5) Compost can also be used as a mulch for nurserymen and vegetable farmers. Compost used as a mulch has advantages over peat moss of bark in that the compost releases absorbed water more readily than does peat moss, and imposes a lesser demand on soil nitrogen than does bark.
(6) Compost is an excellent material for litter or bedding. It is moisture absorbent, odorless, and eliminates the need to purchase bedding from an outside source.
Maximizing the Nutrients Availability from Agricultural Compost:
Digested agricultural compost should be applied at rates to supply adequate nutrients for crop needs. Rates of application greatly in excess of crop needs are undesirable since that means nutrients are not being used effectively and the risk of soil and water pollution is increased. In the past, when manures were valued for their plant nutrients, the normal rate of application was between 25 and 50 tonnes/ha/annum or 5 to 10 tonnes of manure dry matter.
Now manures are often applied in much higher quantities of disposal rates of up to ten times the traditional rates. However, such rates could not be recommended either from an agricultural or environmental viewpoint. Approximately 100 tonnes of 4% dry matter slurry would be required to supply the same quantity of nutrients as 50 tonnes 8% dry matter slurry.
It is clear that the potassium level at this rate is over double the maintenance requirement of most agricultural crops, while the nitrogen and phosphorus rates are high but not excessive. In fact, if only 50% of the nitrogen is available, supplementary fertilizer would be necessary for maximum yield of many crops. If 100 tonnes/ha of pig slurry were used, then 300 kg N, 90 kg P, and 150 kg K would be applied.
In this case, the phosphorus level is in excess of the needs of most agricultural crops but the nitrogen and potassium levels are not excessive. The 100 tonnes of cattle slurry would supply 8 tonnes dry matter and the pig slurry would supply 4 tonnes dry matter per hectare based on dry matter.
The amounts of nitrogen, phosphorus, and potassium in manure are not in the correct proportion for many crops. There is generally too much potassium in cattle slurry and too much phosphorus in pig slurry relative to the other nutrients. To maximize the value of nutrients in manure, cattle slurry should be applied at rates to give adequate potassium for crop need and he supplemented with fertilizer nitrogen and phosphorus.
Pig slurry, on the other hand, should be applied at a rate to supply adequate phosphorus and be supplemented with fertilizer nitrogen and potassium. The same approach can be used to estimate the application rate of other composts so as to maximize the fertilizer benefit of the nutrients present.
Where more composts are available than are required for the crop nutrient needs, most crops will tolerate higher application rates. For example, cattle slurry could be applied at a rate to supply adequate phosphorus for the crop, and the maximum yield when relying on nitrogen from cattle slurry alone, as high rates of application may depress yield.
A dressing of 40 to 50 tonnes/ha of good slurry is suitable for most root crops. As for silage, cattle slurry normally needs to be supplemented with phosphorus and pig slurry with potassium fertilizer. Nitrogen fertilizer may also be necessary, and the rate will depend on crop requirements. Care is needed when using compost for cereals because of their sensitivity to excess nitrogen and the difficulty of applying accurate rates of nitrogen due to the variation in compost composition.
Effect on Soil and Crop:
Composts can have considerable effects on the composition of soils and crops. Soil analyses on experimental plots indicated that land receiving cattle slurry had high soil potassium levels and land receiving pig slurry had high levels of phosphorus. The manganese content of grass from cattle slurry treated plots was significantly lower than with fertilizer treatment.
Copper sulphate is added to the diet of fattening pigs and the slurry may contain several hundred parts per million on a dry matter basis. Crops receiving pig slurry can contain increased levels of copper. There can also be a higher total removal of phosphorus from pig slurry than from fertilizer or cattle manure treatments. The higher phosphorus removal is probably due to the higher soil phosphorus level on pig slurry treatments.
In addition, the slurry provides a micro-environment that can facilitate seedling growth in otherwise inhospitable conditions. It is important to ensure that the ammonia content of the slurry is not so high that it can inhibit seed germination.
Composts can also be used to provide a micro-environment for seedling development in reclamation of land; it can be particularly valuable in the rehabilitation of mine heaps and other industrially disturbed soils. In these situations, the composts are often superior to inorganic fertilizers as they have the dual benefits of improving the physical environment of the plant root and also supplying essential nutrients.
Method of Spreading Compost:
Composts cannot be spread at some stages of crop growth; it is usually not possible to spread composts on manure crops near harvesting time. It is also true that some crops are more suitable for compost application than are others. From a fertilizer point of view, spring application in USA and Europe and kharif (rainy season) application in India usually gives best results, supplying maximum benefit from the nitrogen in the compost.
In pig production, for example, the manure is produced throughout the year, so adequate storage for twelve months would be necessary if all the manure was spread in spring. This would be very costly. In practice, it is customary that manure produced during winter is spread during spring and summer, and that produced in autumn be spread during late autumn. In some situations, where soil conditions are suitable, manure is sometimes spread throughout the year so that very little storage is required.
The pattern of agriculture determines when and where composts can be spread. Traditionally, most compost was spread on tilled land. With intensive agriculture, in areas like the British Isles-compost is spread on grassland. In countries such as Denmark, where most of the land is tilled, a high proportion of the compost is spread for tillage crops. In India, agricultural compost is incorporated in soil for crops.
Time of application of compost is often determined by when soil conditions are dry enough to carry manure spreading equipment. Under some soil and climatic conditions, there may be six months of the year when manure spreading equipment could cause serious damage to the soil surface.
Under other conditions, it is possible to spread manure throughout the year without serious soil damage to grass than the same quantity applied in spring or summer. It appears that slurry can deplete the already low oxygen levels in the soil near the grass roots, killing the better yielding grasses, which will be replaced by weeds. It is therefore advisable that if slurry has to be spread on grassland in winter, low rates (say not more than 20 tonnes/ha) should be used.
Rate of Application:
The quantities of plant nutrients required for different crop and soil conditions are reasonably well established for most countries, where soil fertility is adequate, maintenance dressings of phosphorus and potassium are applied annually. Maintenance dressings are rates that will maintain soil fertility over the years and should equal the difference between losses and the nutrient supplying power of the soil. The main nutrient losses are crop removal and loss in drainage water.
Nitrogen is more complex because there are many sources of losses and inputs and it is the primary nutrient influencing yield in conditions of high soil fertility. With low soil fertility, extra rates of nutrients, above maintenance dressings, may have to be applied initially for maximum crop yield.
Losses of phosphorus and potassium in water from agricultural land are small in comparison with crop and potassium in water from agricultural land are small in comparison with crop uptake and are usually in the region of a few kilograms per hectare per annum. Removal by the crop is related to crop yield and composition. Most agricultural soils can supply large quantities of potassium annually from soil minerals. Rates of nitrogen fertilization for agricultural land are normally less than 300 kg N/ha/annum.
Mineralization of plant nutrients and their availability to plants is one of the major consequences of organic recycling in soil. The quantity released depends mainly on the content of a particular nutrient in organic residues undergoing decomposition. In general, there is immobilization of nitrogen due to decomposition of cereal straw. However, with FYM/compost application no such effect is observed. Addition of FYM and cereal residues results in improvement of total soil nitrogen.
The effect of organic matter in reducing the intensity of phosphate fixation by the soil sesquioxides and maintenance of soil fertility by use of organic manures alongwith superphosphate has also been established. FYM remains intermediate in building up available P status of soil. In sub-humid lateritic soils, P use efficiency under rice-rice sequence was increased tremendously with FYM application. Response of crops to organic manuring depends on degree of decomposition of organic residues, C : N ratio, time of application, soil characteristics etc.
Continuous application of organic manures improves the availability of Zn in soil and may not be sufficient to meet the requirements of the immediate crops. Contrary to macronutrients, the range between deficiency and toxicity limits of micronutrients is quite narrow for most of the crops. Inclusion of micronutrients in fertilization schedule should, therefore be advocated after careful appraisal through soil and plant tests.
Time of Application:
To get a good response from compost application, good management practices should be followed. No more than 50 tonnes/ha should be applied in any one application, and there should be at least 30 days between application. Lower application rates would be advised for wet soil conditions or when applying in the wintertime on grassland. Heavy rates of composts, particularly slurry, can block soil pores.
This can lead to anaerobic conditions and reduced infiltration capacity, leading in turn, to increased surface runoff during rainfall. The blocked soil pores will usually be cleared within 30 days by microbial flora after breaking down the organic matter. However, if compost is applied at too frequent intervals, soil microorganisms will not be able to clear the blocked soil pores.
Cattle or pig slurry at rates of 45 tonnes/ha applied six weeks before cutting did not reduce silage quality or animal performance. In order to reduce surface contamination and disease risks, it is advisable that composts should be applied at least four weeks before pasture is grazed.
Classification of Composting:
It is classified into following general categories:
Composting, categorized by the amount of oxygen available, is either aerobic or anaerobic in nature.
i. Aerobic Composting:
The composting of municipal refuse and large-scale agricultural composts should be carried out under aerobic (with oxygen) conditions. Aerobic composting is governed by the activity of aerobic microbes and hence required the availability of atmospheric oxygen during the period of decomposition.
If the environmental factors are optimal, aerobic composting is characterized by high temperature, the absence of foul odors, and a short stabilization period. The high temperatures have a sterilizing effect by destroying weed seeds and pathogenic organisms.
The Aerobic Heap:
A heap should contain enough bulk of food for the heat-loving bacteria for their growth and activity. If the pile is too small, there will be insufficient heat build-up. To obtain a suitable C : N mix on a garden scale, the materials may first need to be assembled over a period of time. This can best be achieved by creating a preliminary stockpile. Garden debris, mowing, weeds and so forth can be loosely stacked and covered in one pile or placed in plastic bags; likewise kitchen compost.
ii. Anaerobic Composting:
It is governed by anaerobic bacteria that operate in the absence of atmospheric oxygen. The process is characterized by lower temperatures, the production of odorous gases, and longer stabilization times. Since anaerobic composting does not require atmospheric oxygen, the pile or bed can be sealed to prevent the escape of foul smelling gases and left alone. The major advantage of anaerobic composting is that the process can be carried on with a minimum of attention and as such requires little or no energy once the compost bed is established.
The composting process can also be categorized by the operating temperature that exists within the pile. Temperature between ambient and 40°C support mesophilic organisms while temperatures between 40°C and 60°C support thermophilic organisms.
The mesophilic bacteria are more efficient than thermophilic bacteria and, therefore, decomposition occurs more rapidly in the mesophilic region. Those favoring thermophilic composting claim that decomposition proceeds more rapidly at the higher temperatures and in addition pathogens and weed seeds are destroyed.
The temperature in both aerobic and anaerobic composting gradually rises to well within the thermophilic range due to the excess heat energy generated by microbial activity. For this purpose it is essential to understand the effects of temperature and its relationship to microbial activity. Sufficient air is required to sustain the temperature build-up. Compost, which may be ready in two summer months may require six months in winter.
Method of Composting Operation:
The composting processes are operated as either enclosed digesters or windrows.
i. Enclosed Digester:
They are mechanized composters that provide aeration by some type of continued tumbling or stirring action. Some methods combine stirring with forced aeration. Such require a high capital investment and utilize a great deal of energy. Composting times for enclosed digesters are 10 to 15 days.
ii. Windrow Composting:
It is characterized by placing the organic composts in elongated piles called windrows. Depending upon the climatic conditions, the windrows may be placed in the open or covered to provide some protection against the elements.
Aeration is provided by stirring and mixing the composter with a front-end loader or a specially designed rototiller type of implement. If the windrows are adequately mixed, the process will be aerobic and the composting time required is about 6 weeks. By way of contrast, anaerobic windrow composting takes 4 to 6 months.