Concentrated organic manures are those materials that are organic in nature and contain higher percentages of essential plant nutrients such as nitrogen, phosphorus and potash, as compared to bulky organic manures. These concentrated manures are made from raw materials of animal or plant origin. The concentrated organic manures commonly used are- aquatic weeds, oilcakes, blood-meal, fish meal, meat meal and horn and hoof meal.
1. Aquatic Weeds:
Aquatic weeds are still regarded by many people as a menace, because they are not yet aware of the great potential and economic value of these profusely growing, uncontrollable plants. These highly productive plants are generally more productive than conventional field crops. The important aquatic weeds like Azolla pinnata, Eichhornia crassipes (small), E. crassipes (large), Lemna minor, Monochoria vaginalis, Pistia stratiotes, Salvinia sp., Spirodela polyrhiza and Spirogela and Lemna are used as organic manure.
Moreover, when grown on wastes, they do not compete with conventional crops for fertilizer, water or land. Their natural profuse growth in the humid tropical and subtropical areas of the world, requiring no intensive cultivation, makes them a promising source of multipurpose raw material. As a matter of fact, these plants have proved to be good source of livestock feed, human food, fish feed, organic or biofertilizer, energy, fibre and paper.
Furthermore, the aquatic weeds have the capacity to purify waste water through the uptake of dissolved nitrogen, phosphorus and undesirable excessive minerals, including heavy metals. Whereas organic manure has been found to be absolutely essential for maintenance of soil productivity, continuous use of chemical fertilizer, without the supplement of organic manure, has been reported to adversely affect the physical properties of soil. Scientists have been urged to find organic and biological techniques to replace excessive use of chemical fertilizers and pesticides in view of the problems of ecological imbalance.
a. Aquatic Weeds as a Source of Energy:
Fuel from aquatic weeds, even if in a small quantity has economic implications, especially for rural areas in developing countries. Aquatic weeds may be used for biogas production as an organic manure and soil conditioner.
b. Aquatic Weeds as Organic Manures:
Aquatic weeds have been reported to be a good source of organic manure. Many aquatic weeds contain appreciable amounts of nitrogen, phosphorus and potassium. Composted aquatic weeds, when applied to farm land, have been reported to benefit the field crops.
Aquatic weeds not only provide crops with nutrients, they also improve soil’s physical properties like, texture and water holding capacity of soil, which are very important in sandy, lateritic and heavy clay soils widely distributed in developing countries. Azolla, a good source of biofertilizer, is capable of reducing nitrogen demand of soil. Residual effect is also appreciable when aquatic weed compost is added to the soil.
2. Oilcakes:
These can be grouped into two classes, namely:
(i) Edible oilcakes- suitable for feeding the cattle and
(ii) Non-edible oilcakes- not suitable for feeding the cattle.
Edible oil cakes, are normally fed to cattle as concentrates. However, some of the edible oilcakes are also applied by the farmers to the soil. The quantity of nitrogen varies with the type of oilcake. It is from 2.5 per cent in mahua cake to 7.9 per cent in decorticated safflower cake. In addition to nitrogen, all oilcakes contain small percentages of P2O5 (0.8 to 2.9 per cent) and potash (1.2 to 2.2 per cent).
Oilcakes are the quick-acting organic manures. Though they are insoluble in water, their nitrogen becomes quickly available to the plants in about 7 to 10 days after application. The mahua cake however is an exception, as its nitrogen does not become available till about two months after application. As such mahua cake should be applied about two months before sowing, provided the soil is moist. This cake is suitable for application to fruit plants and plantation crops.
These should be well-powdered before application, so that they can be spread evenly and are easily decomposed by microorganisms. They can be applied a few days prior to sowing or at sowing time. Oilcakes- especially groundnut cake, are also applied extensively in the form of a top-dressing to sugarcane. Depending on crop, oilcakes are applied broadcast, drilled or placed while earthing up near root zone.
i. Cattle, Pig, and Poultry Manures:
In general, the higher the dry matter, the higher the nutrient content. For example, in Table 6.2 the higher nutrient content of the poultry manure is due mainly to the higher dry matter content. There is usually about the same level of nitrogen and potassium in cattle slurry, and phosphorus content is usually about 25% of the nitrogen and potassium level. Pig manure usually has about the same level of nitrogen and potassium in cattle slurry, and phosphorus content is usually about 25% of the nitrogen and potassium level.
Pig manure usually has about the same level of nitrogen as does cattle manure, although pig manure is usually higher in phosphorus and lower in potassium than is cattle slurry. The difference in the phosphorus to potassium ratio between cattle and pig manure is principally a reflection of the diet of these animals. The relatively low potassium and high phosphorus in pig slurry reflects mainly a cereal diet, and the high potassium in cattle manure reflects the high potassium content of herbage, which often makes up a high proportion of the ruminant diet.
ii. Poultry:
The nutrient ratio of poultry manure is somewhat similar to pig manure and probably reflects the diets of pigs and poultry. The variation in slurry composition can be greater than for solid manures.
Poultry water can be divided into two parts:
a. Litter Grown:
Most of the poultry produced is grown on litter which absorbs the moisture from the manure. The litter may be sawdust, wood shavings, vermiculite or other suitable material. The spent litter is removed from the buildings depending upon specific management practices and field spread. Waste management of poultry litter is strictly a solid waste handling proposition.
b. Cage Grown:
Some broilers and layers are raised in screened cages, which allow the wastes to drop to a holding pit directly beneath the animals. In some cases, the pit contains water and serves as both a holding and treatment facility. The liquid waste can be pumped into a liquid spreader for field application or into a lagoon for additional treatment.
In other systems, the pits are equipped with ventilation facilities to remove the moisture from the manure, leaving a dry material as the final end-product. The dried manure can be transported and field spread, or bagged and sold as commercial fertilizer. Manure from broilers contains approximately 17 kg of nitrogen 8 kg of phosphorus, and 12.5 kg of potassium per 1000 kg of manure. Manure from layers averages 13 kg of nitrogen, 12 kg of phosphorus, and 11 kg of potassium per 1000 kg.
3. Meat-Meal:
An adult animal can provide 35 to 45 kg of meat after slaughter or death. At present, meat meal is manufactured in India on a small scale. The process of manufacturing meat-meal is very simple. First the bones and the meat are cooked or digested in a special container for two to three hours. The bones are then separated from the meat. This meat is dried on a sand bath till it is brittle and then it is powdered.
The drying can be done in double-jacket trays worked by steam and the material dried over the steam for an hour. Mutton squeezer can also be used for removing water content of the meat, and then dried. Meat-meal is a quick-acting manure and is effective for all crops, on all soil types. Its application is similar to oilcakes. Meat-meal contains about 10.5 per cent N and 2.5 per cent P2Os.
4. Bloodmeal:
An adult cattle gives about 14.0 kg, and a goat or sheep about 1.40 kg of blood. Slaughter-houses should be provided with pucca or concrete floor with a central drain leading into a blood storage tank. The blood is first treated with commercial copper sulphate @ 125 gm per 100 kg of blood. It is then evaporated to dryness on a sand bath.
Next, it is spread on a concrete floor covered by a net, and allowed to dry in sun. When completely dried, it is powdered, bagged and marketed as bloodmeal. Bloodmeal is a quick-acting manure and is effective for all crops on all soil types. It should be applied like oil-cakes. Bloodmeal contains 10 to 12 per cent of N and 1 to 2 per cent of P2Os.
5. Fishmeal:
Non-edible fish carcasses are used to prepare fishmeal. The fish is dried, crushed or powdered and filled in bags. Fish manure is available either as dried fish, or as fishmeal, or powder. The manurial constituents present in it vary with the type of fish. Fishmeal is quick-acting organic manure and is suitable for application to all crops on all soils. It should preferably be powdered before use. Fishmeal contains 4 to 10 per cent N, 3 to 9 per cent P2Os and 0.3 to 1.5 per cent K2O.
6. Horn-and-Hoofmeal:
A healthy animal gives about 3 to 4 kg of horn and hoof. These materials are cooked dried and powdered before bagging. This meal contains about 13 per cent N.