Scientific storage of wheat grains
Raj Pal Meena, Satish Kumar and C.N. Mishra
Agricultural commodities have to undergo a series of operations such as harvesting, threshing, winnowing, grading, bagging/packing, transportation and storage before they reach to the consumers. There are significant losses at all these stages. The most economically important step in case of the cereals like wheat is the storage of the grain produce. Storage is the interim phase in the chain of transporting agricultural products from farmers to consumers. Losses during the storage constitute a significant share of food grain loss in post production operations. With the production of nearly 87 million tonnes of wheat India has potential to meet the food requirement of the country. Losses in wheat production are generally noticed at various stages like threshing, transport and storage. Also the attack of rodents and birds lead to losses in grain production of wheat. Losses during storage are mainly due to attack by storage insect-pests, loss of moisture in grain, fungus infestation, rodent attack, and spillage. Since a huge amount of the wheat produce is lost during the storage of grains, various precautions need to be taken to prevent these losses.
The time of harvesting in wheat plays a vital role. Wheat crop should be harvested, when the crop is at field maturity and grains become hard. If wheat crop is harvested before proper maturity, it leads to low recovery of grain, higher proportion of immature seeds, poor quality seeds, with high moisture content, that are prone to diseases during storage. But a delay in the harvesting causes shattering losses and exposes the wheat grains to birds, rodents and insect and pest attack. Therefore harvesting should be done in dry conditions at maturity so that the moisture content of the grains is optimum. Threshing and winnowing should be done in the fields to avoid losses. Direct sun drying and excessive drying should be avoided and the grains should be packed in sound clean gunny bags to minimize the losses.
Wheat grain is commonly contaminated with:
1. Smut balls - Wheat plants infected with smut fungi produce smut balls and when fully developed these are of the size of the kernels. The internal part of the seed is replaced by the smut spores and produce off-colour flour when milled thus reducing the market value. These can be removed from wheat grain, either by screening or by wind.
2. Ergot bodies - Ergot bodies are hard, spur like, purplish black structure which replaces the kernel on grain head. These fungal bodies contain alkaloids that may lead to poisoning on consumption.
3. Mouse droppings - Mouse droppings are black and of various shapes and sizes. These are commonly present in wheat that has been stored for long time.
4. Chaff - Chaff consists of broken wheat plant parts and the glumes (papery bracts) which enclose the kernels. These are usually easy to remove by winnowing/or screening except where the kernels are enclosed by the glumes.
5.Insect parts - Insect legs, body parts etc are commonly found in wheat fields and since these are lighter in weight, can be easily removed by fanning.
In India, about most of farm produce is stored by farmers for their own consumption. Farmers store grain in bulk, using different types of storage structures made from locally available materials. Storage structure design and its construction also play a vital role in reducing the losses during storage. The major construction materials for storage structures in rural areas are mud, bamboo, stones, and plant materials. They are neither rodent-proof, nor secure from fungal and insect attack. Some of the major considerations in building a storage structure to reduce storage losses are:
- The storage structure should be elevated from the ground and away from moist places in the house
- As far as possible, the structure should be airtight, even at loading and unloading ports
- Surrounding area of the structure should be clean to minimize insect breeding
- Rodent-proof materials should be used for construction of rural storages
- The structure should be plastered with an impervious clay layer to avoid termite attack, or attack by other insects.
- Various research and development organizations in India have identified some proven, age-old structures from certain areas of the country and based on these, some improvised storage structures have also been developed and recommended for use at farmer level.
The storage methods vary from mud structures to modern bins. Grains can be stored indoors, outdoor or at underground level.
Indoor storage involves grain containment in structures like Kanaja, Kothi, Sanduka and earthern pots. Kanaja is a grain storage container made out of bamboo. The base is usually round and has a wide opening at the top which is plastered with mud and cow dung mixture or covered with paddy straw or gunny bags. Sanduka, the wooden boxes with the capacity of 3-12 quintals are used for storing small quantity of grains. Kothi an indoor strorage structure is constructed with a large door for pouring grains and small outlet is made for taking out the grains. Earthen pots made locally using burnt clay are indoor storage containers for storing small quantity of grains, when arranged are arranged one above the other they are known as dokal.
Outdoor storage of grains is done in structures made of bamboo or straw mixed with mud. Gummi is an outdoor structure that is made with bamboo strips or locally available reeds, usually circular or hexagonal in shape and plastered with mud used for storing grains. Kacheri is a traditional storage structure using paddy or wheat straw, woven as rope. Hagevu is an underground structure that is used to store grains. It is a simple pit lined with straw ropes to prevent damage from moisture.
It is important to note that these indigenous storage structures are not suitable for storing grains for very long periods. Regular mud plastering is required for a variety of indoor and outdoor storage containers and structures for increasing their life span and ensuring safe storage of grains.
Improved grain storage structures
With several problems associated with traditional modes of grain storage some modifications have been done to offer improved grain storage structures to the farmers. For small-scale storage of grains the PAU bin, Pusa bin and Hapur tekka may be used. The PAU bin designed by Punjab Agricultural University is a galvanized metal iron structure and the capacity ranges from 1.5 to 15 quintals. Pusa bin is a storage structure is made of mud or bricks with a polythene film embedded within the walls. While the Hapur tekka is a cylindrical rubberized cloth structure supported by bamboo poles on a metal tube base, and has a small hole in the bottom through which grain can be removed.
Large scale grain storage is done in CAP and silos. CAP Storage (Cover and Plinth) involves the construction of brick pillars to a height of 14" from the ground, with grooves into which wooden crates are fixed for the stacking of bags of food grains. The stacks are covered with 250 micron LDPE sheets from the top and all four sides. Food grains such as wheel, maize, gram, paddy, and sorghum are generally stored in CAP (cover and plinth) storage for 6-12 month periods. It is the most economical storage structure and is being widely used by the FCI for bagged grains. The structure can be fabricated in less than 3 weeks. It is an economical way of storage on a large scale.
The silos are either metal or concrete. Metal silos are cheaper than the concrete ones. In silos the grains in bulk are unloaded on the conveyor belts and, through mechanical operations, are carried to the storage structure. The storage capacity of each of these silos is around 25,000 tonnes.
Stored grain pest and their management
The grain produced by farmers is destroyed by pest, rats and moisture. It is important to prevent the storage losses through scientific methods and better management. Mainly khapra bettle, red flour beetle, lesser grain borer are the main pest which destroy stored grains. These insect along with by eating also affect the quality of food grains. Due to moisture & fungus also food grains because unsuitable for human consumption. Also the germination capacity of seed declines. Food grains generally and wheat specifically can be secured through following methods:-
- Dry the grain properly under bright sun shine so that it should not contain moisture more the 10%.
- Clean the grains before storage.
- Use new gunny bags to fill the grains. Used bags should be disinfested by dipping them in 1% malathion solution before reusing them.
- Bullock carts, tractor, truck or other vehicles used for the transports of grains should be cleaned before carrying the grain.
- Properly clean the storage house, remove the cracks & fill the rat burrows with cement.
- White wash the storage house before storing grains & spray Malathion @ of 50 E.C. 3Lt. per 100 Sq. meters.
- Place the heap of bags 50 cm away from wall and in between the heaps give some gaps. Also there should be a gap between the roof and the bags.
- Grain remains pest free by using Neem seed powder.
- To kill rats zinc phosphide and warfarin should be used.
Control after attack of pest:-
Even after using above methods the attack of pest is observed than use fumigants.
It is available in markets in form of tablets as Celphos tablets. One 3.0g tablet releases 1.0g gas in moisture. This gas is lighter than air so it remains at the surface of food grains. It should be dispersed from bottom to top. 1 or 2 tablets are sufficient for 1 ton wheat grain. After applying the tablets the air tight storage house should be close for at least seven days.
Ethylene Dibromide (E.D.B.) Ampule:-
This fumigant is appropriate for small storage. It is available in market in 3, 6, 15 and 30 ml ampule. 3ml chemical is used for 1 Qtl of grain. The gas released by this chemical is six times heavier than air. So it is used at upper surface to get dispersed towards the bottom. The ampule is placed in grain and is broken by pressing. After this the storage house is closed. If grain is stored in heap of bags the E.D.B. ampule is used at the rate of 10 Millilitre per cubic meter and is covered by the help of polythene covers, the grain can be effectively saved from the damage of insect pests.
By scientific ways of storage significant amount of wheat grain can be saved. To become self-dependent in food grain and improve the economic condition of country, it is necessary to check the losses/deterioration of food grain from harvesting to consumption.
Raj Pal Meena, Satish Kumar and C.N. Mishra
Directorate of Wheat Research Karnal – 132 001