- Rice crop should be harvested when the grains become hard and have about 20 % moisture in them though the plants still remain green.
- Usually the crop comes to harvesting between 25 - 30 days after completion of flowering.
- Harvesting is generally done when 85% of the grain is straw colored or 2/3 of the rachis (main axis of panicle) is dry.
- If the crop is harvested early, the produce contains high moisture and more Immature grains.
- The yields will be low due to unfilled grains. It is very difficult to store produce as shriveled grains with high moisture are prone to primary infestation of Pests.
- If the crop is harvested early, the produce contains high moisture and more Immature grains.
- The yields will be low due to unfilled grains.
- It is very difficult to store produce as shriveled grains with high moisture are prone to primary infestation of Pests.
- Late harvesting results in shattering of the grains, germination even before harvesting during rainy season and breakage during processing.
- Hence harvesting at correct time is essential to get good quality grains and higher yield.
- Crop can be harvested at physiological maturity or at harvest maturity.
- Crop is considered to be at physiological maturity when the translocation of photosynthate is stopped to economic part.
- The moisture content falls steeply from 40 per cent to 20 per cent which is an indication of attaining physiological maturity.
- Harvesting time generally depends on season, temperature, rainfall, available sunshine and cultural practices.
- 7 - 10 days prior to harvesting, the water from the field has to be let out and the soil is allowed to dry.
- The dryness of soil facilitate easy harvesting of the crop nearer to the ground level.
Criteria for harvesting
- Should be carried around 32 days after flowering.
- Green grains not more than four to nine per cent.
- Percentage of milky grains less than one per cent.
- Moisture contents of grains less than 20 per cent.
- 80 per cent panicles straw colored and grains in lower portion of panicle in hard dough stage.
- At least 5 hills are to be studied at maturity.
Method of Harvesting
- Harvesting is done either Manually or by Mechanical means.
- In manual harvesting, sickle is the most important tool.
- The sickle has to be sharp, curved and serrated for efficient harvesting.
- In the event of labour shortage or in periods of peak labour demand mechanical harvesting is favored.
- Combined harvestor are used for harvesting. Combines perform several operations.
- It cuts the crop, separates the grain from straws, cleans it from chaff and transports the grains to the storage tank.
- The combines only reaps 2 - 9 rows at a time depending on its size and horse power.
- Use of these combines for harvesting is limited to large holdings.
- The simple machines useful for harvesting in small holdings are also available.
- These machines cost about Rs. from 25,000 to 40,000.
- These machines are run by diesel oil.
- With these machines in a day of 6 hours about 1 hectare can be harvested.
Self propelled paddy reaper
- During peak harvesting season when a large area comes for harvesting at a time, farmers are facing problems due to labour shortage.
- To over come the above problems there is a need for Mechanical paddy harvestor
- The machine can be recommended for harvesting paddy in all types of soils except in black cotton soils when the soil moisture is more than 25%.
- The machine will not cut lodged crop.
- The reaper for harvesting paddy at high soil moisture conditions is similar to that of self propelled vertical conveyor reaper.
- Modified cage wheels (with leaf type lugs) were provided.
- Here the drive for cutting mechanism is taken from 5 H.P diesel engine.
- The engine runs at 1500 RPM.
- The machine has gear drive to the driving wheels.
- The drive is taken to the cutter bar and conveyor belts through bevel gear system.
- The speed reduction from engine to ground wheels and to cutter bar is done with the help of belts, pulley and set of gears.
- The reduction from engine is such that the machine speed in the field is about 2 to 3 Km/hr and the cutter bar speed is about 300 strokes per minute.
- Two clutches are provided for easy turning.
- A main clutch is also provided to disengage the drive whenever it is not required.
The I.R.R.I. model paddy harvester
- It runs by a 5 H.P. diesel engine and requires one man to operate the machine.
- It cuts the paddy crop and leaves it on the field in windrows on one side of the machine.
- Before harvesting the corners of the plot should be harvested manually so that the machine will enter the field and is enable to turn at the corners.
- The field coverage capacity is 4 acres/day.
- But this machine is suitable only when the field is completely dry at the time of harvesting.
- If there is high soil moisture in the field then the machine will not work and also it is not suitable for harvesting paddy in coastal Andhra Pradesh during the Kharif season where paddy is harvested even in water logged conditions.
- The cost of the machine is about Rs.32,000/-.
- This machine is commercially manufactured by M/s. Swathi Industries, Coimbatore .
Problems in Harvesting
- Problem arises especially when it coincides with heavy rain or cyclones.
- The crop may be submerged and the seeds may start germinating on the plant itself.
- This can overcome by growing dormant varieties.
- The other way of saving the crop is by spraying 500 ltr/ha of 25 per cent salt solution at harvesting maturity by 8 days.
- After harvesting, the cut plants are spread in the field and after 2 - 3 days they are piled up in the threshing floor (or) in the field itself.
- Depending on the marketing position and environmental conditions threshing may be undertaken from 15 days to 2 months from the time of pileing.
- Immediate threshing after harvesting results in less broken rice.
- Delayed threshing deteriorates the quality of the grain.
- For manual threshing we can use threshing table.
- This is commonly followed because of the time and labour saving.
- The thresher is made up of a combination of several different machines, each having a special and separate function to perform in the separation of the grain from the straw.
- The thresher is a very efficient machine, when properly operated and given reasonable care it is durable and given a high degree of performance.
- It not only threshes, separates, but also cleans the grain thoroughly.
- It also delivers the straw to the stack.
Functions of Thresher
- The work performed by a thresher can be divided into four separate functions, which are To feed the grain to the threshing cylinder.
- To thresh the grain out of the head
- To separate the grain from the straw
- To clean the grain and delivered it to the outlet.
- In the cleaner, the grain passes over a series of sieves and screens through which flows a stream of air created by a fan.
- The larger and heavier sections of straw are held on the sieves, while the blast of air blows out the finer chaff.
- The width of the thresher at the cylinder and at the rear determines its size.
- By changing the speed (revolution per minute) of the cylinder and changing the sieves and screens, a thresher may be adapted to thresh different crops.
Multi crop thresher
- This machine is useful for threshing paddy, wheat, maize, jowar, bajra, ragi and others quickly and economically, it can work with either a 5 HP electric motor, or diesel engine.
- The crop is manually fed into the threshing cylinder. In case of paddy and wheat,the entire crop is fed through the machine..
- Quantities of various crops that can be threshed per hour are; paddy 6 to 8 quintals, Wheat 4 to 6 quintals, Jowar 10 to 12 quintals and Maize 10 to 12 quintals.
- The approximate cost of the machine is Rs. 30,000/-
Japanese paddy Peddle
- This is manually operated, is also used for threshing small quantities of harvested paddy.
- A single person with the help of a pedal operates this thresher.
- Threshing of paddy is done by holding the bundle of sheaves against the teeth of revolving drum.
- Power operated threshers are also available now a days and they are being used for threshing and also winnowing The machines having 5 HP power are able to thresh 6 - 10 quintals of rice in an hour. 4 persons are required to feed the sheaves into machine.
- This type of machine cost about Rs. 35,000/- exclusive of motor.
- Drying is a process which reduces moisture content from grain to safe limit.
- Drying process is basically the transfer of heat by converting the water in grain to vapour and transferring it to the atmosphere.
- Threshed paddy or boiled paddy required drying.
- It is essential that drying is gradual and slow in the initial stages in order that the milling quality is not adversely affected.
- When paddy is relatively dry, it can be dried further rapidly without damaging the grains.
- High moisture in the grains as well as high humidity in the atmosphere cause sprouting and molding of grain.
- This problem can be overcome by mixing powdered common salt at 5 Kg/100 Kg of grain.
- The salt absorbs water from the grain and salt solution flows out of the heap of grain.
- This treatment prevents heating and subsequent damage to the produce.
- Another way of storing wet paddy is by mixing paddy husk, which helps in storage for about seven days.
- Artificial drying by using the steam to dry the produce, can be done at any time of the year, but is expensive.
- Timing Dry paddy as soon as possible to 18% moisture content to decrease discoloration, spoilage and sprouting. Moisture content target.
- Do not dry below 14% MC - unless for long term seed storage - over dried grain will crack upon readsorbing moisture from the atmosphere and thus will have a lower head rice recovery when milled.
- Do not mix grain of different moisture contents as this causes moisture absorption by the dry grain and results in grain cracking. Drying temperature and rate.
- Set operating temperature initially at 150ºF (65ºC).
- As the grain dries out, or when moisture has dropped to 18%, turn down drying air temperature to 110ºF(43ºC) to prevent fissuring of the grain.
- At 65ºC, the drying rate is about 1% moisture per hour.
- At 43ºC, the drying rate is about 0.5% to 0.75% moisture per hour.
- If there is no great urgency, fuel costs can be reduced by using ambient air (if relative humidity is less than 70%), once the grain moisture has reached 18%.
- Then, slow dry the grain with ambient air until moisture reaches 14%.
- Drying Options - flat bed dryers, recirculation dryers, sun drying.
Drying is done either by using
- Solar energy or by Artificial heating.
- Sun-drying is carried out by the farmers on public roads or on made-up floors under uncontrolled conditions. Rice millers invariably use concrete floors for drying.
- Such drying results in sun-cracks and contamination on quality of rice is little realised as much of the milling is in hullers which by themselves contribute to breakage. Dependence on sun for drying also means break in operations when sun is not available.
- In case of sun drying the produce is spread on hard floor or threshing yard around 10-cm thickness, and is allowed to dry by heat supplied by the sun.
- If high moisture continues to remain in rice after harvest, it would undergo spoilage because of high temperature, respiration rate and microbial activity, and the presence of foreign matter. Hot spots often develop in concentrations of foreign material
- In general, four to five days of sun drying is required for different produce to bring the moisture to a safe level. In tropical regions, one-day drying under full sunshine throughout the day brings down grain moisture content of rice from 24 per cent to 14 per cent.
- hough sun drying is cheaper, there are some problems. The grains that are in the upper layers develop fissures due to uneven sun-drying resulting in broken grains. However, this problem can be overcome by repeated stirring.
Artificial Drying methods
- Flow drier heated by paddy husk.
- Batch drier heated by either furnace oil or paddy husk.
- Mobile driers heated by paddy husk.
- Unheated air drier. Portable driers is a recent development. Bagged raw paddy or paddy in bulk can be dried with these driers by keeping the air temperature at 55º-60ºC. It takes about 1 hour for reducing the moisture by 2 per cent from 22 per cent and later on one hour for every one per cent. The driers being portable, handling and transport costs are considerably reduced.Avoid grain from overheating.
Drying for seed
- Timing Dry paddy to 18% moisture content as soon as possible (especially during periods of inclement weather, and when grain has moisture above 21%) to decrease discoloration, spoilage and sprouting.Moisture content or not dry below 14% MC - unless for long term seed storage - over dried grain will crack and re absorb moisture from the atmosphere and thus will have a lower head rice recovery when milled.
- Drying temperature and rate Drying at 110ºF (43ºC)
- The drying rate of a flatbed dryer is about 0.5% to 0.75% moisture per hour.
- If the initial moisture content is 21%, it will take about 10 to 14 hours to dry the grain to 14%.
- Dry the grain continuously until moisture of grain near the blower end of bin has reached 14%.
- If blowers are delivering the correct air volume, it is not necessary to mix the grain.
- However, more uniform drying can be attained if the grain is mix at least once, halfway during the estimated drying period. Monitor the drying progress with a moisture meter.
- Flatbed dryers, recirculation dryers, sun drying
- Maintain genetic purity by preventing mixing or contamination with other seeds. Clean and grade seed to produce uniform sized seed grains.
- Store seed and protect it, if necessary from bacterial and fungal growth, and infestation by mites and insects with the proper seed protection chemicals.Hygeine about the seed storage area is critical.
- Clean the grain to remove chaff and light impurities.
- Maintain genetic purity by preventing mixing or contamination with other seeds.
- Depending on the available equipment, the cleaned grain is further processed to separate slim grains in a thickness seperator such as a slotted screen or thickness grader, and a length grader such as an indented cylinder.
Principles of Cleaning
- The separation of undesirable material and seeds from desirable seed in an air screens machine is done on the basis of differences in seed size and weight.
- Screen machine uses three cleaning elements.
- The light seeds and chaff material is removed from the seed mass through aspiration.
- In this operation, the seeds are dropped through screen openings, but the larger material (trash, clods etc.,) is carried over the screen into a separate short.
- In this operation, the good seeds ride over screen openings, while smaller particles (under sized, cut, shriveled, broken seeds) drop through.
- Cleaning Equipment
- The air screen cleaner
It has the following main components
- Feed Hopper, Screens, Square mesh, Rectangular mesh, clay-crushing rolls, brushes, tappers & shoes.
Rice is stored in the forms of paddy or rough rice, milled raw rice, milled boiled rice, bran, broken grain either on the farm or in the mills and in commercial warehouse.
- Paddy is stored either for seed or for hand pounding or for milling as needed.
- Rice (husked rice), either semi-polished (4-5% removal of bran) or polished (10 - 12 % removal of bran), is stored in jute bags.
- According to the consumers' liking the raw rice has to be stored for at least over a year before it is consumed while with parboiled rice no such condition is needed and is consumed as fresh.
- In store the rice develops rancidity and heating due to either insect attack or excess moisture.
- The rice can safely be stored in warehouses without reduction in quality and quantity of rice.
- If the warehouses are not aerated or damp-proof, the free fatty acid rises from initial 35 to 320.
- The rice becomes unacceptable when acid reaches 350 unless it is remilled.
Broken's are of two types - big broken's are generally over 1/4 the size of the kernel and small broken's are less than 1/4th.
- These are graded and filled in separate jute bags.
- The normal storage period for broken's is 2 to 6 months because they develop rancidity very soon.
- Bran can be stored for short period because it develops rancidity very fast.
- It is always better to dispose it off within a week's time after it is obtained from mill.
- The key to good storage is hygiene and grain moisture contents.
- The target moisture for storage is less than 14%.
- The following table shows the storage possibilities and problems associated with difference grain moisture contents.
Grain moisture content (%)
||> 1 year
- Calculation of moisture content
Moisture content can be on a wet (MC wet) or dry (MC dry) basis:
- MC wet = Weight of moisture in wet grain * 100/(weight of wet grain)
- MC dry = Weight of moisture in wet grain * 100/(weight of dry grain)
- Grain moisture depends upon the temperature and the relative humidity of the air.
- The following table shows this relationship.
Hygiene for storage
- Keep storage areas , crevices, wooden pallets etc clean by spraying with the recommended insecticide to disinfect insect breeding places.
- Place sticky traps in the drying and storage areas for rats.
- Storage rooms should be physically rodent and bird proof, if possible.
- If necessary, treat storage sacks with insecticide to prevent insect infestation.
- This however is a dangerous practice if there is a chance that the seeds will be milled for consumption, and therefore is not recommended.
- Inspect the stored seeds once a week for signs of insect infestation.
- If there is infestation, under the direction of a trained pest control technician, the storage room or the seed stock may be enclosed hermetically with tarpaulin and fumigants.
- Phostoxin is used by the grain milling industry.
- This will kill all insects, larvae, and rodents in the enclosure.
- For long term seed storage, store the seeds in bags in storerooms with controlled temperature and relative humidity.
- The recommended storage environment for rice seeds are less than 20ºC and 40% R.H. In this conditions both fungi and insects will be inhibited.
The difference constituents of rice undergoing storage are
- Milled-raw rice,
- Milled-boiled rice,
- Paddy is stored either on the farms or in the rice mills.
- Rice undergoes storage at the mills and in commercial warehouses.
- Bran, brokens and germs are stored only in the mills from where these are sold and for end use.
- A sizeable quantity of paddy is held on the farms either as seed, or for hand-pounding or for milling and consumption, as required, paddy harvested in October-December is mostly retained on the farms. Summer and autumn crop paddy is not held on the farms, because of drying problem and susceptibility to discoloration.
Storage in farms
- On the farm, paddy is stored indoors in jute bags or in containers made of rope (morai), straw (Bharola), bamboo (Kanagi) or mud (Kuthla or Kuthi).
- When quantities held in storage exceed a tone, the containers made of rope, straw or bamboo are used and these are placed out doors.
- The outdoor containers are covered with a sloping straw roof. Capacity of the out door containers ranges between 1.5 and 10 tones.
- To avoid storage losses, use of either cement or steel bins are recommended.
Storage in mills
- In the mills, paddy is placed in chambers or in the open either loose or in jute bags.
- The period of storage in the mills ranges between 2 and 8 months.
- Paddy kept in the chambers without adequate protection from pests and moisture sustain a loss both in quantity and quality.
- In the open, weather conditions cause either sprouting or discolouration.
- Birds, rats, monkeys, squirrels, and insects attack paddy kept in the open and cause quantitative losses and also contaminate the grain with undesirable substances.
- Storage in Ware houses Paddy stored in warehouses which are damp and rodent-proof, suffered a loss only on account of reduction in moisture content.
- In these warehouses, paddy filled in jute bags is placed in standard-sized lots of 6x10x6 m.
- For keeping paddy in the open, land that is not susceptible to flooding is selected and is paved either with bitumen or with bricks.
- Paddy filled in jute bags is then placed in lots of 6 (breadth) x 10 (length) x 7 (height) m after arranging either wooden pellets or concrete blocks on the ground that provide for a air-gap of 15 cm between the floor and the bag.
- The lots are then covered with polythene to protect the grain from weather and pests.
- The loss in this storage is observed to be only quantitive and brought about by reduction in moisture content.
- It has been possible to hold large quantities of paddy free of spoilage for a year in this type of plastic storage which does not have a conventional roof over it and is exposed to the weather.
Storage in silos
- Silos have been used for storage of paddy in India during the last few years.
- These are either steel or concrete circular silos, capacity ranging between 350-600 metric tones (for wheat this capacity is 500-850 metric tones).
- Initially, flat bottom silos were used with provision of screw conveyors at the bottom to take paddy out.
- Unloading of paddy from flat bottom silos was found slow and labourious.
- Only hopper bottom silos are now in use for paddy storage.
- The silos storage unless adequately understood and properly supervised results in discolouration and spoilage of paddy.
- The funnelling, takes place while unloading operations are in progress, leaves some paddy undistrubed on the sides of the silos.
- Special arrangements are necessary to effect a turn-over for the paddy that remains on the sides of the silo.
- In a silo, paddy can be stored in the same condition and without any loss in quantity.
- It is also possible to adjust the condition of paddy at the time of delivery with the result that maximum out-return of rice can be obtained from such paddy in the course of milling.
Cost details of different storage methods
Conventional warehouse (storage in jute bags)
Silo (Concrete) (Storage in loose)
Plastic storage with concrete flooring (storage in jute bags)
|1. Initial construction
|2. Interest depreciation and maintenance
|3. Storage charges per tonne per year (including loading in and out charges)
|Total storage cost (2)+(3)
- There is no alternative at present to storage of rice in jute bags.
- Bulk storage of rice has not been possible so far because of deleterious effects of mechanical pressure.
- Unpolished or brown rice can be stored for short periods provided the bran layer is intact.
The rice moved and/or a stored in India
- Semi-polished (4 to 5 per cent removal of bran) or
- polished (10-12 per cent removal of bran).
- Traditionally, consumers prefer raw rice that has undergone storage over a year.
- In case of boiled rice, the preference is for fresh milled rice.
- In storage, rice tends to develop rancidity and heating as a result of either insect attack or excess moisture.
- Presently, sizeable quantities of semi-polished raw and boiled rice are held in buffer storage for periods varying between 4 and 20 months.
- It is noticed that with standard storage practices (IS 6151-I-71) in
warehouses that are well-aerated and damp proof as well as rodent-proof, when the stack size is 10 m x 6 m and height is 16 bags, and when initial moisture is not in excess of 14 per cent and insecticidal treatments are carried out in time, the only loss to rice in storage is that brought about by reduction in moisture content.
- When storage is done in warehouses that are neither aerated nor damp-proof, in storage of 6 months, free fatty acidity rises from initial 35 to 320.
- Rice becomes almost unacceptable when it reaches 350, unless it is re-milled.
- Rice that is polished is less susceptible to development of rancidity on storage up to two years.
- Brokens are graded either as big or small.
- Big brokens generally are over 1/4th the size of the kernel and small brokens less than 1/4th .
- All brokens are packed in jute bags and the filling ranges between 75 and 90 Kg.
- Brokens, particularly small brokens develop rancidity very soon.
- The normal storage period is 2-6 months.
- Insects are mainly responsible for causing deterioration in storage.
- Spoilage, is heavy, wherever bird and rodent damage exists, causes sizeable quantitative loss.
- The demand for brokens being good, the aim generally is to dispose of these as quickly as possible.
- When the demand slows down, however, alternative uses for brokens will need attention and then production of clean brokens and grading them to set standards would assume significance.
- There is a greater danger in brokens of quantititive and qualitative loss, due to insects, rodents and birds, as compared with rice.
- Bran is filled in jute bags of 60-70 kg capacity.
- Bran obtained from huller mills is cleaned and disposed off in week's time as cattle/poultry feed.
- Bran from disc huskers and rubber-roll shellers is used mainly for oil-extraction and subsequently is either exported or used as cattle feed.
- Bran is not kept in storage for long because of rapid development of rancidity.
Factors affecting storage
- Several factors that influence the storage of food grains are moisture content, quality of produce, climate, storage conditions.
- The most important factors deciding the storability of the produce is moisture content of grains.
- High moisture content of grains results in severe attack of insects and microorganisms in addition to heating and germination.
Moisture content of paddy for safe storage
- Paddy , Raw Rice 14%
- Parboiled Rice 15%
- Among the climatic factors
- R.H. are important factors influencing storage of food grains.
- Respiration of grains increases with increase in temperature.In addition temperature influences the metabolism, growth, development, reproduction behaviour and distribution of insects.
- Insect development is generally limited below 10ºC and above 45ºC.
- Light influences movement and development of stored grain pests. In case of rice storage insects show photo negative response. Darkness is necessary for egg laying.
- Under high R.H. moisture content of grains increases.
- Tropical climate, in which temp and R.H. are high, are favourable for the growth and multiplication of insects.
- Because of favourable conditions throughout the year, pest problem is continuous and high in tropical regions compared to temperate regions.
Storage practices in India
- The storage function is as old as man himself, and is performed at all levels in the trade.
- Producers hold a part of their out put on the farm .
- Traders store it to take price advantage.
- Processing plants hold a reserve stock of their raw materials to run their plants on a continuous basis.
- Retailers store various commodities to satisfy the consumers day-to-day needs. Consumers, too, store food grains, depending on their financial status.
- The storage of agricultural products is necessary for the following reasons.
- Agricultural products are seasonally produced, but are required for consumption throughout the year.
- The storage of goods, therefore, from the time of production to the time of consumption, ensures a continuous flow of goods in the market.
- Storage protects the quality of perishable and semi-perishable products from deterioration.
- Some of the goods, e.g., woollen garments, have a seasonal demand.
To cope with this demand, production on a continuous basis and storage become necessary.
- It helps in the stabilization of prices by adjusting demand and supply.
- Storage is necessary for some period for the performance of other marketing functions.
- For example, the produce has to be stored till arrangements for its transportation are made, or during the process of buying and selling, or the weighment of the produce after sale, and during its processing by the processor.
- The storage of some farm commodities is necessary either for their ripening (e.g., banana, mango, etc.) or for improvement in their quality (e.g., rice, pickles, cheese, tobacco, etc.), and storage provides employment and income through price advantages.
- For example, middlemen store food grains by purchasing them at low prices in the peak season and sell them in the other seasons when prices are higher.
Risks in Storage
- The storage of agricultural commodities involves three major types of risks. These are as follows.
- The risks of loss in quantity may arise during storage as a result of the presence of rodents, insects and pests, theft, fire, etc.
- Dehydration too, brings about an unavoidable loss in weight.
- It had been estimated that about 10 million tonnes of food grains are lost every year because of poor and faulty storage.
- The second important risk involved in the storage of farm products is the deterioration in quality, which reduces the value of the stored products.
- These losses may arise as a result of attack by insects and pests, the presence of excessive moisture and temperature, or as a result of chemical reaction during the period of storage
- Dehydration of fruits, vegetables and meat during storage may lower their sale value.
- Butter , if not properly stored, may become rancid, which reduces its sale value.
- The loss in the quality of farm products varies with their quality at the time of storage the method of storage and the period of storage.
Price risk in storage
- This, too, is a important risk involved in the storage of farm products.
- Prices do not always rise enough during the storage period to cover the storage costs.
- At times they fall steeply, involving the owner in a substantial loss, Farmers and traders generally store their products in anticipation of price rise and they suffer when prices fall.