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Post-harvest losses account for about 10% of total food grains due to unscientific storage, insects, rodents, micro-organisms etc., In India, annual storage losses have been estimated14 -million tones worth of Rs. 7,000 crore in which insects alone account for nearly Rs. 1,300 crores. The major economic loss caused by storage insect pests is not always by consumption but also by the amount of contamination. About 600 species of insects have been associated with stored grain products. Nearly 100 species of insect pests of stored products cause economic losses. In India annual storage losses have been estimated14 -million tons of food grain worth of Rs. 7,000 crore every year in which insects alone account for nearly Rs. 1,300 crores. According to World Bank Report (1999), post-harvest losses in India amount to 12 to 16 million metric tons of food grains each year, an amount that the World Bank stipulates could feed one-third of India's poor. Out of these post-harvest losses storage -insects alone account for 2.0 to 4.2 per cent followed by rodent’s 2.50per cent, Birds 0.85 per cent and moisture 0.68 per cent.
Types of storage losses
Insects cause different kinds of losses viz.
- Quantitative loss
- Qualitative loss
- Loss of seed viability
- Damage to storage structures
- Direct feeding insects cause loss in weight of the stored grains
- A rice weevil will eat 14 mg out of 20 mg of a rice kernel during its developmental period.
- But commercially the whole grain is lost
- A female weevil, through three generations per year, has the biotic potential to reproduce 1,500,000 offspring which will consume 1,500,000 kernel of rice (amounting 30 kg of rice)
A gravid female of Sitotrogacerealella can destroy 50 g of rice completely in 3 generations
- Direct feeding on the grain
- Chemical changes in grain content
- Contamination of grains with moult skin and body parts
- Spreading the pathogenic micro-organisms
- Loss of seed viability
- Insects were found to cause the loss of viability of seeds to an extent of 3.6 to 41 % in paddy
Damage to storage structures
- Insects like Lesser grain borer has the capability to destroy the wooden storage structures, containers polythene lined bags etc.,
- Food losses -Direct or Indirect losses:
- A direct loss is disappearance of food by spillage, or consumption by organisms including insects.
- An indirect loss is the lowering of quality to the point where people refuse to eat it.
SIGNIFICANCE OF INFESTATION
- Weight loss
- Germination loss
- Commercial value loss
- Consumer preference loss
- Nutritional values loss
- Facilitates fungal growth
- Storability loss.
FoodGrains can be stored in bulk or in bags.
(a) Bulk (open) storage:
Farm products are sometimes stored in surface structures in a loose form. It is preferred over bag storage for the following reasons
Large quantities of food grain can be stored. No difficulty in loading and unloading of grain. No need to purchase storage containers like gunnies. Insect incidence is less than bag storage, even this can be eliminated by fumigation in situ. Avoids waste from leaking bags. Easy inspections- save labour and time.
(b) Bag storage
Storage farm products are stored after placing them in gunny bags made of jute.
Each bag contains a definite quantity which can be bought, sold or dispatched without difficulty. Bags are easier to load or unload.Infested bags-can be removed and treated easily. Problem of the sweating of grains does not arise because the surface of the bag is exposed to the atmosphere.
Storage structures used by the farmers are
- Gunny bags of different capacities (35, 50, 75 and 100 kg) with or without inside
- Plastic lining.
- Mud bins having 100 – 1000 kg capacity
- Baked earthen containers of 5- 100 kg capacity
- In heaps on flat floor in the corner of houses (100- 1500 q).
- Bamboo structures
- Wooded bins and
- Underground structures
CONVENTIONAL STORAGE STRUCTURES
Split bamboo woven in the form of a cylinder with wide base and narrow mouth
Paddy, wheat and sorghum
Life 4-5 years. Weight loss due to insect attack is 5 % in paddy and 15 % in sorghum.
Mud and earthen structures
Clay, straw and cow dung- 3:3:1. earthen structures are made, sun dried and then burnt in fire
Paddy, wheat, sorghum, oil seeds and pulses
5 - 10 quintals
Life 8- 10 years. During rainy season develop cracks and moisture absorption followed by insect and mould infestation.
Local wood is painted black. At the top, 30cm x 20 cm inlet and at the bottom 30 cm x15cm outlet is provided
15- 20 years. Neither airtight nor moisture proof.
Rectangular, structures built as part of the house, with brick in cement or lime mortar having a wall thickness of 40 –50 cm. At the top 50x 50 cm inlet and at bottom 15 x15 cm outlet is provided.
Paddy, sorghum and wheat
25- 30 quintals
25- 30 years. High initial cost, not insect and moisture proof.
Circular pits vary from 100 – 400cm in depth and 50 – 100cm dia at neck and250 – 300 cm at the bottom. For filling and emptying there is an opening at the top. Before filling the sides and bottom are packed with straw and husk. After filling the pit is gain covered with straw and stone, the finally with mud.
100 –200 quintals
Safe against insects but, loss of seed viability and handling difficulties made it out of date
Miscellaneous plant materials
a. Paddy straw
b. Stem of vitex and pigeon pea stalks
c. Bottle gourd shells
a. Paddy straw is wound in the form of rope to varying diameter
b. stems wound like a bin and both sides are plastered with mud and cow dung
c. empty shells are used
Paddy, other cereals and pulses
Pulses, gourd seeds
Not insect and rat proof
Only small quantity of seed lots.
Metal corrugated G.I. sheets
Sheets of about 3 m high are held vertically along one edge and edges of the other sheets are overlapped and bolted to each other. Thus the circle with 2-4 m dia. is completed with many such sheets. They are covered on the top with the plain M.S. or G.I. sheets.
Various types of grains
Hessian cloth bags
Improved rural-level storage structures
1. Bitumen/ coal tar drum
- An alternate model of metal bin, low cost with similar technical performance.
- These bins are of 520 mm dia and 900 mm height. They can store 1.5 q of wheat and 1.2q of Bengal gram.
2. Hapur bin/ Kothis
- Circular bins of 2, 5, 7.2 and 10 q capacities and have potential to meet requirements of even large farmers.
3. Udaipur bin
- These bins are made out of used coal tar drums.
- These can stock 1.3 q of wheat and maize.
- These bins can be made to have more airtight lid if the drum outlet end is given small cut to unload the bitumen.
- These bins are suitable for storing of food grains for short duration and can be adopted by small farmers.
4. Stone bin
- Stone bin (Chittore bin) is made of locally available 40 mm thick stone slabs with dimensions of 680 mm x 1200 mm with square cross-section.
- The inlet and outlet are made of asbestos. This bin has a capacity of 3.8 q.
5. Bamboo bin
- These bins are made of two walls of bamboo with polythene lining in between and have varying capacities.
- These bins are suitable for short – duration storage and can be adopted by small and marginal farmers.
6. Baked clay bin
- Baked clay bin of 7q capacity (paddy) is made of 16 burnt rings jointed by mud plaster; cement mortar and cow dung coatings one after another.
- The ends of the rings are made in such a manner that they fit into each other.
- These rings are kept on a polythene sheet covered and plastered platform of brick mansory and cement sand mortar.
- An outlet is provided for the discharge of the grain.
- The top is covered with a mild steel lid. Because of the low cost and good performance these are particularly useful for small and marginal farmers who do not store their produce for longer duration.
7. PKV bin
- Made from green bamboo splits into suitable sizes.
- The tunnel, outlet flap valve and complete stand can be fabricated in a workshop.
8. Pusa bin
- It is a modification of the ordinary mud storage structure commonly used in villages.
- To provide moisture proof and airtight conditions, polyethylene film of 700 gauge thickness has been embedded at the top, bottom and on all the sides of the mud bin.
- The embedding process provides mechanical support and safety to polyethylene film.
- The construction of outer walls with burnt bricks up to 45 cm height makes the structure rat proof as well.
- The bin is constructed with un burnt bricks on burnt bricks or concrete floor to avoid rat burrowing.
- The grain and seed both remain safe in the bin for more than one year with proper precautions.
9. Pusa Cubicle
- This is a room like structure ( 3.95 x 3.15 x 2.60 m), a modification of Pusa bin to provide large storage capacity of 24 tonnes on a platform of 3.73 m x 2.93 m x 0.07 m is made with unburnt bricks on a concrete floor (except 22 cm of outer sides with burnt bricks).
- A polyethylene sheet is placed on this platform and another platform of similar dimension is made with unburnt bricks.
- The 22 cm thick inner walls are constructed upto 2.6 m height. A wooden frame of 1.89m x 1.06 m for door is fixed in the front side of 3.95 m wall.
- The roof can be made by wooden beam placed at 15 cm distance and covered with unburnt bricks.
- Presently storage is practiced in small compartments of a room (5.3 m x 2 m x 4 m) called kothar.
- The roof is constructed with the help of wooden poles and mud slabs, leaving near the front wall three filling holes each of 0.5 m x 0.5 m size.
- Two out lets of G.I. sheets of 15 cm dia. and 30 cm length are fitted at the floor wall on the front side.
11. Metal bins
- Bins made of steel, Aluminum R.C.C are used for storage of grains outside the house.
- These bins are fire and moisture proof.
- The bins have long durability and produced on commercial scale.
- The capacity ranges from 1 to 10 tons. Silos are huge bins made with steel/ aluminum or concrete.
- Usually steel and aluminum bins are circular in shape.
- The capacity of silo ranges from 500 to 4000 tons. A silo has facilities for loading and unloading grains.
- Food grains have to be stored and preserved on scientific lines in godowns till they are issued to consumer.
- Te bags containing food grains cannot be just dumped inside the godown, for it will not facilitate proper storage.
- Proper stacking ensures free access to the stocks in all parts of the godown for inspection and helps in effective disinfestations work. Generally, three methods of stacking are being followed: 1. Simple, 2.Cross and 3. Block method.
Steps necessary for good storage practice in respect of all food grains
- Stored product pests can be managed either behaviorally (traps viz., probe traps, light traps, pitfall traps etc.,) or with several preventive and curative measures (both chemical and non-chemical methods).
- Once a facility is obtained, a number of steps are to be taken to ensure safe storage of grains. These steps comprise
1. Before storage
- Checking for leakage of rain water and sufficiency of drainage facilities
- Cleanliness of the facility and environment
- Assessment of capacity of the facility
- Pesticidal treatment
- Security and firefighting arrangements and
- Repairs to available equipment
2. After receipt of grain
- Inspection for variety and soundness of quality
- Inspection carefully for infestation, it any, and when present, for type and extent
- of infestation,
- Inspection whether grain has excess moisture, whether it had been heated up in
- earlier storage and has any musty or rancid odour
- Any grain rendered wet or damaged to be segregated and salvaged with facilities
- available and check the weight received
3. During storage
- Maintenance of cleanliness
- Ensuring aeration where necessary
- Checking for leakage after rains
- Inspection for insects, rats and mites at fortnightly intervals
- Watch for advancement in deterioration, if any,
- Pesticidal treatments necessarily based on observations
- Ensuring disposal where called for, and
- Arrangement for segregation, salvage and processing, wherever, damage owing to leakage of water and other causes might have taken place.