The storage of farm produce like crops and other agricultural products for food in periods of scarcity and famine is probably as old as agriculture. The need for the storage and preservation of agricultural products has been necessitated by:
The alternation of cycles of favorable and unfavorable periods for the optimum growth and production of crops as characterized by the dry and rainy seasons in the tropics and the winter and summer in the temperate regions
By vagaries of nature such as floods, drought or major pest and disease outbreaks causing complete crop failure.
Poor farm produce storage is one of the major causes of food shortages and low agricultural supply in the world. According to the Food and Agricultural Organization (FAO), post-harvest losses for grains amounted to over 200 million tons yearly, yet only about 20 million tons of grain are enough to feed adequately a population of 500 million for one year.
In developing countries loss of agricultural products during storage could amount up to 30% for grains and up to 50% for root and tuber crops. These figures indicate the importance of food storage if the country is to feed its rapidly growing population and attain some level of food sufficiency and security.
This article explains the importance of storage, short and long term methods of grain storage, pest and rodents of importance in grain storage, integrated method of rodents control and safety measures during carrying out rodent control programme.
Meaning of Storage
Storage may be defined as the act of preserving and keeping agricultural produce or any commodity for future use without necessarily losing its quality. There should be little or no change in chemical or physical condition as to reduce its quality.
Thus, the main objective of storage is to preserve the produce such that it will still be valuable and useful to the ultimate consumer.
The Role of Storage of Farm Produce in the Economy
In most countries grains are among the most important staple foods. However they are produced on a seasonal basis, and in many places there is only one harvest a year, which itself may be subject to failure.
This means that in order to feed the world’s population, most of the global production of maize, wheat, rice, sorghum and millet must be held in storage for periods varying from one month up to more than a year.
Grain storage therefore occupies a vital place in the economies of developed and developing countries alike.
1. To Stabilize the Prices
The market for food grains is characterized by fairly stable demand throughout the year, and widely fluctuating supply. Generally speaking, people’s consumption of basic foods such as grains does not vary greatly from one season to another or from year to year.
The demand for grain is ‘inelastic’, which means that large changes in the market price lead to relatively small changes in the amount of grains which people purchase.
2. Even Out Fluctuations in Supply
Market supply, on the other hand, depends on the harvest of grains which is concentrated within a few months of the year in any one area, and can fluctuate widely from one year to the next depending on climatic conditions.
New varieties that have shorter growing periods, and variation in climatic conditions and farming systems in different regions of a country, can help to even out the fluctuations in market supply.
The main function of storage in the economy is to even out fluctuations in market supply, both from one season to the next and from one year to the next, by taking produce off the market in surplus seasons, and releasing it back onto the market in lean seasons; this in turn smoothes out fluctuations in market prices.
The desire to stabilize prices of basic foods is one of the major reasons why governments try to influence the amount of storage occurring, and often undertake storage themselves.
3. Avoid Wastage of Produce
Storage prevents wastage of output especially highly perishable product such as vegetables and fruits.
Storage preserves products and ensures freshness and good quality. Effective storage encourages farmers to produce more leading to high income, living standard and general wellbeing of the society.
The Different Storage Methods
The different storage methods include but not limited to the following;
1. Traditional Farm/Village Storage Methods
1a. Temporary Storage Methods
Such methods are quite often associated with the drying of the crop, and are primarily intended to serve this purpose. They assume the function of storage only if the grain is kept in place beyond the drying period.
i. Aerial Storage
Maize cobs, sorghum or millet panicles are sometimes tied in bundles, which are then suspended from tree branches, posts, or tight lines, outside or inside the house.
This precarious method of storage is not suitable for very small or very large quantities and does not provide protection against the weather (if outside), insects, rodents, or thieves.
ii. Storage on the Ground, Or On Drying Floors
This method can only be provisional since the grain is exposed to all pests, including domestic animals, and the weather.
Usually it is resorted to only if the producer is compelled to attend to some other task, or lacks means for transporting the grain to the homestead.
iii. Open Timber Platforms
A platform consists essentially of a number of relatively straight poles laid horizontally on a series of upright posts. If the platform is constructed inside a building, it may be raised just 35-40 cm above ground level to facilitate cleaning and inspection.
Platforms in the open may be raised at least 1 meter above ground level. They are usually rectangular in shape, but circular or polygonal platforms are common in some countries.
Grain is stored on platforms in heaps, in woven baskets or in bags. In humid countries fires may be lit under elevated platforms, to dry the produce and deter insects or other pests.
Instead of being horizontal and flat, the platform may be conical in shape, with the point at the bottom. Up to 3 meters in diameter, such platforms facilitate drying because of their funnel shape at the top.
They consist of a frame of horizontal poles which is square, circular or polygonal in shape, against which the timbers which form the cone rest. These timbers meet at the bottom on a wide central supporting post.
Platforms with roofs (but no walls), of whatever shape or form, may be regarded as transitional types between temporary and long-term stores.
In southern Benin, Togo and Ghana, for example, maize cobs in their sheaths are laid in layers on circular platforms with their tips pointing inwards.
The platforms are usually between 2 and 3 meters in diameter, but some may be more than 6 meters wide, with a maximum height of 2.5 meters at the centre and 1.5 meters at the periphery. In Ghana such a granary is called an “ewe” barn.
1b. Long-term Storage Methods
i. Storage Baskets (Cribs) Made Exclusively of Plant Materials
In humid countries, where grain cannot be dried adequately prior to storage and needs to be kept well ventilated during the storage period, traditional granaries (cribs) are usually constructed entirely out of locally available plant materials: timber, reeds, bamboo, etc.
Under prevailing climatic conditions most plant material rots fairly quickly, and most cribs have to be replaced every two or three years – although bamboo structures may last up to 15 years, with careful maintenance.
Basically similar to the outdoor type of platform described above, in all its variations, the traditional crib differs in always having a roof and wall(s).
It may even be elevated at least one meter above ground level, with a fire maintained underneath to assist drying of the contents and, allegedly, to reduce insect infestation. However, such cribs (especially the larger ones) are more commonly raised only 40 to 50 cm above ground level.
Access to the interior of a crib is gained usually over the wall. This may involve raising the roof, but some cribs have a gap between the top of the wall and the roof to facilitate entry.
Relatively few cribs have sealable gaps in the wall or floor for the removal of grain.
ii. Calabashes, Gourds, Earthenware Pots
These small capacity containers are most commonly used for storing seed and pulse grains, such as cowpeas.
Having a small opening, they can be made hermetic, by sealing the walls inside and out with liquid clay and closing the mouth with stiff clay, cow dung, or a wooden (cork?) bung reinforced with cloth.
If the grain is dry (less than 12% moisture content) there is usually no problem with this kind of storage.
These are large clay receptacles whose shape and capacity vary from place to place. The upper part is narrow and is closed with a flat stone or a clay lid: which is sealed in position with clay or other suitable material.
Generally kept in dwellings, they serve equally for storing seeds and legumes. So that they may remain in good serviceable condition, they should not be exposed to the sun and should not be either porous or cracked.
iv. Solid Wall Bins
Such grain stores are usually associated with dry climatic conditions, under which it is possible to reduce the moisture content of the harvested grain to a satisfactory level simply by sun-drying it.
Solid wall bins are therefore traditional in the Sahel region of Africa, and in southern African countries bordering on the Kalahari Desert.
The base of a solid wall bin may be made of timber (an increasingly scarce resource), earth or stone. Earth is not recommended because it permits termites and rodents to enter. The better base is made of stone.
Mud or clay silos are usually round or cylindrical in shape, depending on the materials used. Rectangular-shaped bins of this type are less common, because the uneven pressure of the grain inside causes cracking – especially at the corners.
Clay, which is the basic material, varies in composition from one place to another. That most commonly used for such construction work is obtained from termitaries, because the termites add a secretion which gives it better plasticity.
To give it added strength, certain straw materials such as rice straw may be mixed with it; while, in some countries, néré juice is added to make it almost as durable as concrete. The diversity of materials used explains why the capacities of such silos can vary from 150 kg to 10 tones.
The roof is usually made of thatched grass, with a generous overhang to protect the mud wall(s) from erosion. Where a side door or a detachable ‘cap’ is not provided, the roof has to be lifted for access to the bin. Such silos can serve for 30 or even 50 years.
v. Underground storage
Practiced in India, Turkey, Sahelian countries and southern Africa, this method of storage is used in dry regions where the water table does not endanger the contents. Conceived for long term storage, pits vary in capacity (from a few hundred kilograms to 200 tonnes).
Their traditional form varies from region to region: they are usually cylindrical, spherical or amphoric in shape, but other types are known. The entrance to the pit may be closed either by heaping earth or sand onto a timber cover, or by a stone sealed with mud.
2. Alternative Storage Technology at Farm/Village Level
Wherever grain is grown on a commercial basis, buying agencies often issue empty sacks to producers so that they may be filled on the farm.
The buying agency may then collect the bagged grain from the farm, or the producer has to deliver it to the nearest collection point.
In either case, the producer has to store the sacks of grain for some time before they are sold. During this period precautions have to be taken to ensure the safety of the grain and maintain its quality.
At the very least, the bagged grain must be kept off the ground to prevent spoilage by translocating water and/or termites.
Low platforms, tarpaulins or plastic sheeting may serve this purpose; but if there is a risk of damage by rodents or other animals, high platforms fitted with rodent barriers should be used.
If there is a risk of rain during the temporary storage period, the bags should be covered with waterproof sheeting (but not all the time if the grain has moisture content much in excess of 12%).
Alternatively, the sacks of grains should be stacked on dunnage or waterproof sheeting, away from walls, in a rodent proofed barn. The need for chemical methods of pest control should not arise if the storage period is short.
Where sacks are used for domestic grain storage, similar conservation measures should be adopted. However, it will be necessary to employ some form of insect pest control. Second-hand sacks must be thoroughly cleaned and disinfested before use.
2b. Metalor plastic drums
Drums are often used as storage containers in the house and serve notably for the storage of cereal seeds and pulses.
Plastic drums are used intact or after having the upper part cut off to facilitate loading and unloading.
Otherwise, plastic lends itself poorly to adaptation because it is relatively weak at most, a lockable outlet can be added. If the lid is tight fitting and the drum is completely filled with grain, any insects present will deplete the oxygen in the drum and die.
Metal drums can be adapted for domestic grain storage in a similar way. A removable lid permits easy loading, but it is also possible to weld half of the lid to the rim of the drum, and provide a riveted hinge on the remaining half of the lid so that it alone can be opened.
Fitted with a padlock, such a modified drum is more secure. To make a store of greater capacity, two metal drums can be welded together end to end and fitted out as described above. Well modified and/or fitted with gaskets, metal drums can also be made airtight.
Inaccessible to rodents, efficient against insects, sealed against entry of water, drums make excellent grain containers. However, they should be protected from direct sunshine and other sources of heat to avoid condensation by being located in shaded and well ventilated places.
2c. Alternative solid wall bins
In some countries grain storage workers, rather than modifying traditional storage structures, have developed significantly different storage bins. A few examples of these are described below.
i. The “Pusa” bin
Developed by the Indian Agricultural Research Institute (I.A.R.I.), these silos are made of earth or sun-dried bricks; they are rectangular in shape and have a capacity of 1 to 3 tonnes.
A typical “Pusa” bin has a foundation of bricks, compacted earth, or stabilised earth. A polyethylene sheet is laid on this, followed by a concrete slab floor 10 cm thick.
An internal wall of the desired height (usually 1.5 to 2 metres) is constructed of bricks or compacted earth, with a sheet of polyethylene wrapped around it.
This sheet is heat-sealed to the basal sheet, and the external wall is then erected. During the construction of the wall an outlet pipe is built into its base.
The concrete slab roof is supported by a wooden frame and, like the floor, is constructed of two layers separated by a polyethylene sheet. During its construction, a man-hole measuring 60 x 60 cm is built into one corner.
The “Pusa” bin has been widely adopted in India, and has been demonstrated in some African countries. It gives good results when loaded with well dried grain.
ii. The “Burkino” silo
Based on a traditional dome shaped type of bin, this silo is constructed with stabilized earth bricks. Various models and capacities are available.
The base is made of stabilized earth resting on the ground or on concrete pillars. The dome shaped roof is also made of stabilized earth bricks, using special wooden formers.
The technique of making a dome-shaped roof is not easy to master, and usually has to be done by skilled masons. A variant has been developed with the roof resting upon a wooden frame, which can be erected by unskilled farmers.
iii. The “USAID” silo
This silo is based on the “Burkino” silo and examples have been erected in Nigeria, holding one ton of maize grain, the silo rests on stone or concrete pillars supporting a reinforced concrete slab 1.5 meters in diameter.
The walls are made of stabilized earth bricks and are plastered inside and out with cement reinforced with chicken wire mesh.
The top is dome shaped with a central round opening, and covered with a cone- shaped earthen cap. This is plastered with cement, and rests on bamboos or on a metallic drum base.
An outlet door, consisting of a 15 x 30 cm plate 1.5 mm thick which is smeared with grease for easy sliding, is let into the base concrete slab.
iv. Concrete/cement silos
Such silos are ‘cement rich’, and often include other materials which normally have to be imported into developing countries. Therefore they are potentially (and usually) expensive structures, which can be seriously considered only when improvements to traditional storage bins cannot be practically applied.
Their redeeming feature, given that they are properly constructed and used, is that they are robust and should give many years of satisfactory service.
v. The Ferro cement bin (“Ferrumbu”)
Developed in Cameroon and tested in a number of African countries, this bin is similar to the “Burkino” bin in shape but consists mainly of chicken wire plastered inside and out with cement mortar.
The wall varies in thickness from 3.5 cm for a bin of 0.9 m3 capacity, to 6 cm for one of 14.4 m3 capacity.
vi. The “Dichter” stave silo
This cylindrical silo was developed in Benin, and is constructed with trapezoidal section concrete blocks (staves) supported externally by tightened steel wire.
Both internal and external surfaces are rendered smooth with cement, and the outside may be treated with coal tar to ensure water-proofness.
The floor and cover slab consist of reinforced concrete cast in-situ, and the whole structure is raised off the ground on four concrete block pillars. A manhole is located in one side of the cover slab, and an ‘anti-theft’ outlet is built into the bottom of the wall.
A principal technical difficulty with such bins is that they are poorly insulated, which encourages the development of moulds if the moisture content of the grain is higher than 13%.
This means that the bins must be constructed indoors, or at least protected by shelters with a wide overhang to reduce extreme variations in temperature. With tall bins, such as the larger Ferrumbu, this is not very practical.
vii. Metal silos
Economically valid for storing large quantities (over 25 tons), metal silos are often regarded as too costly for small scale storage. Nevertheless certain projects have been successful in introducing small metal silos, of 0.4 to 10 tons capacity, at farm/village level in developing countries.
Such silos are made of smooth or corrugated galvanized metal, and are cylindrical in shape with a flat metal top and, usually but not always, a flat metal bottom.
A man-hole with a cover, which may be hinged but is nevertheless lockable, is located, usually to one side, in the top panel; and an outlet pipe provided with a padlock is fitted at the base of the wall.
Metal silos should be placed on platforms or plinths, to facilitate emptying. Large capacity silos are usually constructed without base plates on raised concrete slabs. In this case, bitumen or cement mortar is plastered around the base of the wall to prevent penetration by water and pests.
As with concrete silos, it is essential to provide cover, to avoid excessive variations in temperature and moisture translocation.
viii. Synthetic silos
Various attempts have been made to develop small scale storage bins, using synthetic materials such as butyl rubber and high density polyethylene.
However, such bins proved to be either too expensive or prone to damage by pests. Also the management level required by such storage facilities is probably too high for most rural situations.
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