Harvesting Rice, Agri-Crop

harvesting, threshing, drying, milling, storing, cleaning

We can determine the best time to harvest based on the maturity date of a given variety or by examining the panicle if all the grains are ripened. Rice should be harvested when 80-85 percent of the grains turned yellow. The grain moisture content ideally is between 20-25% MC. If the crop is too dry,  when these are rewetted, they break when milled resulting in low quality and low milling recovery. The table below shows the different rice varieties and their maturity date after planting.

        Table of different rice varieties and their maturity period

Variety	Maturity date	Variety	Maturity date
IR 36	110	IR 66	108
IR 42	135	BPIRi10	108
IR 64	113	PSBRc10	106
PSBRc	123	PSBRc 34	124
PSBRc 18	123 -130	PSBRc  28	111-118
PSBRc 82	110-117	NSICRc 112	111-118
NSICRc 122	121-128	PSBRc 84	111
PSBRc 78	111	PSBRc 80	112
PSBRc 88	116	Mestizo	107

In dry season harvest, an optimum time of harvest 28 - 35 days after heading gives best grain germination and head rice. In wet season harvest, optimum time is 32 - 38 days after heading.     

 

Methods of Harvesting Rice

1. Manual is the method of harvesting rice with the use of sickle and scythe.
2. Mechanical is the method of harvesting rice with the use of a reaper or combine harvesters.

Whatever method is used in harvesting always take note of the following:

• Harvest at the right time and moisture content (20-25% MC). Too early harvesting results in difficulty in separating grains from the panicle and immature grains from the head will be ground during milling.
• Avoid delays in threshing after harvesting, within an  overnight that the harvested rice is stacked specially if it is wet, the grain quality is affected.
• Use the proper machine in threshing. There are some machines that allow lots of grain to go with the hay during threshing.
• Clean the grain properly after threshing.

Harvesting could be done through the following:

         

1. Manual harvesting and stacking, followed by threshing and cleaning by hand. This includes the use of traditional tools for threshing such as racks, simple treadle threshers and animals for trampling. This method has been a thing of the past due to intensive farm mechanization.
2. Manual harvesting followed by threshing and cleaning with a threshing machine. All threshing machine now includes a simultaneous cleaning of the grains.
3. Mechanical harvesting using a rice reaper and threshing by a threshing machine and by using a combine harvester. The combine harvester will combine all operations: cutting, handling, threshing ,and cleaning.

List of advantages and disadvantages of common harvesting system

Method	Description	Advantages	Disadvantages
1. Manual harvesting and threshing	·   Cutting, stacking, bundling, handling and piling by hand ·   Threshing by beating ·   cleaning by winnowing	·   Efficient ·   Most effective in lodged crop ·   Less weather dependent	·   High labor cost, skill dependent ·   Susceptible to grain damage ·   Winnowing/cleaning necessary
2. Manual harvesting and threshing/cleaning by machine	·   Cutting and stacking by hand ·   Threshing by machine	·   More effective in wet season harvest, wet crop conditions ·   Higher capacity than manual ·   Lower labor requirements	·   Higher capital cost ·   Dependency on availability of contractor ·   Less dependent on field size
3. Standard combine harvest	·   Harvests, threshes, and cleans crop mechanically ·   Transport harvested grains in convenient area.	·   High output, timelines attained ·   Produces clean grain ·   Spread straw back in the field, which will ensure a good source of organic material to the farm.	·   Higher cost ·   Less effective in partially lodged crop

Note: Avoid burning of rice material wastes such as the hays, hulls, and other materials. Farm wastes burning is regarded as one of the big contributors to global warming.

 Threshing

           Given the high labor requirements of manual threshing, in many countries, threshing of rice is now mechanized by use of small stationary machine threshers. Stationary threshing is generally done in the field or near or at the field side.

          In many regions, machine threshers are owned by individuals who offer custom operations to farmers. This requires that farmers schedule harvesting dates depending on the availability of the thresher. Many threshers are mounted on tractors to quickly move from field to field. Some are still drawn by a carabao especially on muddy areas.

Guidelines for  Threshing

Timing of threshing is very essential. Ideally, threshing should begin immediately after cutting . Immediate threshing reduces the exposure of crops to insects, birds and rodents, disease, and molds. Crops that are piled over a period of time generates heat that will serve as an ideal medium for growth of molds, disease, and pests. Piling for several days will lead to grain discoloration, germinated grains, and spoilage.

1. After harvesting, thresh the rice immediately. Threshing is the process of detaching and separating rice grains from the panicle.
2. Threshing can be performed manually or mechanically. The manual methods of threshing are treading by feet, flail treading and beating stalks against tubs, threshing board, or racks.
3. In treading by feet, rice grains spread on the threshing floor is trampled upon by human feet. The continuous treading action of one person separate about 14 kg of grain from the straw in one hour.
4. In animal treading the harvested rice is laid around a stake or pole with the panicles toward the stake. A team of animals (carabao, cow) is driven slowly around the stake to trample the grain off the straw. The palay is raked occasionally until the grain is completely threshed, and all the straw have been removed. Many of the grains may be damaged due to the hard hooves and heavy weight of the carabao.
5. In flail treading, grain separation is done by beating the paddy with a stick or hinged device called flail.
6. Another method is through the impact of rice heads beaten against a solid object (hampasan method). A simple way to do this is to beat the rice panicles with a stick. The method can thresh 20-60 kg of palay per person per hour.
7. One low-cost mechanical thresher you can use is the pedal-powered model. It has a low initial cost and one worker can thresh about 1-2 cavans per hour with this model.
8. Another low-cost model is the throw-in axial flow thresher. This is portable, weighs about 100 kg and requires a 5-7 horsepower engine. It has a higher output of up to 600 kg/hour.
9. The most commonly used mechanical thresher are lightweight which could be drawn by a carabao or a tractor in a muddy field powered by a diesel engine and could finish threshing harvest of 2 ½ hectare in one day, if it is dry, and 1 ½ hectare if wet. Be sure to lay plastic sheet in the area to minimize grain losses.

10.Using the combine harvester, it could finish harvesting and at the

      same time threshing   with a minimum of 3 hectares per day.

          Factors to consider in choosing the appropriate system of threshing:

1. availability of labor
2. capital outlay of the farm
3. timeliness of harvesting
4. field layout and field accessibility (combine harvester requires a certain field layout and access)
5. rice variety (some varieties are more prone to lodging)
6. demand for quality rice
7. demand for straw (some threshers damage the straw making it less available).

Grain Cleaning is the removal of unwanted materials from the grain such as straws, chaffs, unfilled grains, weed seeds, soil, rubbish, and other impurities.

1. Clean the grains immediately after threshing. Cleaning is an essential post-harvest operation since it affects storability and milling quality of grains. Uncleaned grains are prone to deterioration during storage.
2. In some mechanical threshers cleaning is carried out simultaneously with threshing. However, in manual or animal treading, further cleaning is necessary because the grain is mixed with straw, chaff, dirt, stones, and other impurities.
3. The most common method of cleaning rice grains in the Philippines is the use of winnowing basket (or Bilao). Winnowing sieves called bithay, made either of wire mesh or bamboo slats are also used for cleaning.
4. Another method is the use of hand operated winnower or hunkoy. This gadget consists of a paddle-type fan mounted on a wooden frame to direct air blasts against the grain or foreign matter that falls from the hopper.

Importance of Cleaning Rice grain

1. Clean grain has higher market value.
2. Clean grain is easier to dry.
3. Clean grain has better storability.
4. It produces better quality of milled rice.
5. It reduces dockage at time of milling.
6. Seed cleaning will reduce susceptibility to diseases and  will improve germination .

         

          Methods of Cleaning

1. Winnowing. Lighter materials such as unfilled grains, chaffs, weed seeds, and straw can be removed from the grain by using a blower, air fan, or by wind. Recover only the heavier grains.
2. Screening/sifting. Using  sifter or a net smaller materials such as weed seeds, soils particles and stones can be removed by sieving the grain through a smaller sized screen (1.4 mm or less sieve opening).
3. Blowing.Using the thresher or mechanical blower to clean the rice grains  and using its blower to remove all unfilled grains , weed seeds, and chaff.

Drying

           In tropical country like ours grain drying is not so much a problem. But in the advent of climate change, extreme weather conditions often prevail. Stormy weather prevails even during harvest season. This situation threatens the vulnerability of rice production. A lot of harvest immediately could turn into a lower quality. After harvest when the grain is re-wet high temperature occurs and excessive grain moisture content causes deterioration of rice grain . To ensure quality grains and to prevent spoilage, clean and properly dry the harvested and threshed grains immediately. The approximate moisture content of the crop at harvest time is 20-25%. The right moisture content (MC) for storage is 14 percent.

          Importance of Drying Rice Grains

1. Improves the storability of grains
2. Obtains higher market value
3. Prevents pest infestation and damage caused by microorganisms
4. Proper drying minimizes breakage or improve milling output and quality

          Methods of drying

1. Solar or sun-drying. Traditionally, this method has been used by the farmer using nylon net and plastic sheets to sundry the grains. It is the basis of majority of farmers then to schedule their harvest due to scarcity of drying materials. With the fast construction of concrete solar driers and concreting of farm to market roads, sun drying is now a minimal problem. In solar drying, spread the cleaned grains in a layer 2-4 cm thin on various surfaces such as fish nets, canvases, threshing floors or on pavement. Stir the grains regularly (30 min. interval) to allow uniform drying. Dry grains under the sun for 1-2 days frequently turning over the grains for uniform drying. Traditionally, farmers determine the right moisture content by biting the grain if it is brittle. This method usually results in a lot of losses because grains were pulverized and thrown away when vehicles pass.

   

2. Mechanical dryer. If harvest occurs during the rainy season, when sun drying is not feasible, use a heated air dryer. Use batch dryers, since these are relatively cheaper and easier to operate. When using mechanical dryers, observe the recommended drying air temperature by the manufacturer. If using a mechanical dryer farmers should group themselves and make a schedule to be able to meet the maximum capacity of the dryer for more efficient and economical operation.

      Dry rice grains 8-11 hours with the use of mechanical dryer to obtain 14% moisture content for safe storage. Do not over dry rice grain, if the grain is meant to be milled.  Moreover, if the grain is not allowed to cool after drying they are brittle and will break easily if milled immediately. To obtain high milling recovery, allow to temper overnight before milling.

Storing

          Though majority of the farmers don’t store their whole produce, it is a must to store a certain percentage for their own consumption. Businessmen engaged in rice grain trading buy the farmers produce and store the grains in large warehouses. Storing grains is to keep it for future use. It is better to store it unmilled to maintain its quality and palatability. Stored rice is affected by moisture, temperature, insect pests and type of storage facilities. Moisture content greatly affects the keeping quality of rice. High moisture during storage generates heat which makes rice grains susceptible to insect pests and molds as well as yellowing and discoloration. Mold growth in rice causes loss of luster, bad odor, loss of viability, and the production of mycotoxins, which poison animals and pose health hazard to people. Reducing moisture content, however, is not sufficient to guarantee long and safe storage, because rice absorbs or gives off moisture depending upon the temperature and relative humidity in the storage area. Thus, suitable containers and structures should be used. In order to prevent heavy losses during storing, here are the guidelines to follow:

1. After drying the rice grains, store them properly if you are not going to sell immediately. Safe storage involves the preservation of the quality and quantity of grain for future use. Thus, protect your harvest from bad weather, pests, microorganisms, chemicals, moisture, and other types of contamination.
2. Clean sacks before use to remove insect pests.
3. Do not stack the sacks of rice on a concrete floor, it will accumulate moisture. Use a stacking tray made of wood.
4. Separate old and new grain stocks.
5. Separate and mark different varieties by storing them in different sacks. Handle sacks with care to avoid damage and spillage.
6. Cover the stacked bags of rice with plastic sheet or other covering materials.
7. Clean bodega/warehouse prior to new grain storage and maintain cleanliness of the surroundings to discourage rodents’ infestation.
8. Visit the storage area regularly to observe any grain damage, changes in grain temperature, increase in moisture content, and any indication of grain deterioration.
9. Avoid storing fertilizer and insecticides near the rice stock to ensure safety and maintain market quality.

10.  Make use of a bait for rodents if necessary.

Milling

          It is one of the thriving rice related business. Rice milling is the removal of hulls and bran from rice grains to produce polished or white rice ready for human consumption. The rice bran is a very important ingredient in feed formulation for animal production. The farmers utilize it as a direct feed to their farm animals. The rice hull is being used as a good substitute for firewood in cooking.

Depending upon the equipment used, milling operation involves cleaning, hulling, grain separation, whitening or polishing, and to some extent grading.

          There are three types of milling in the country under the introduced technology: the kiskisan, the cono and the combination of rubber-roll-huller and horizontal whitener. Additional improvement with the machinery is the attachment of stoner to remove small pebbles being mixed to the grains during drying. Before, you need to transport your rice grains to the nearest rice mill to avail its services. Now with the proliferation of the travelling rice mill, they provide the services to the doorsteps of their customers.

          To obtain high milling recovery, observe the following:

1. Clean and dry grains immediately after harvest. Allow to temper overnight or longer before milling to minimize grain breakage.
2. Do not mix different varieties. Mixed varieties adversely affect the performance of the mill.

Health and Safety Precautions  During Harvesting and other Post Harvest Activities

          Practicing safety precautions will save lives and suffering.

Manual Harvesting

          When cutting crop with a sickle, always hold the stems with thumb pointing upward, away from the sickle/scythe. Be extra careful in pulling the scythe to prevent injury. Always have a piece of  long sleeved clean cloth, hat,  and sunglass, as protections from excessive heat of the sun

Machine Threshing

1.       Become familiar with the machine before the first operation. Read the manual that came with the machine.

2.       Do the pre-operational check-up of the machine before starting the engine.

3.       Do not wear loose clothing that may be picked up by moving parts.

4.       While operating, keep all shields and guards in place

5.       Never leave the thresher unattended while the engine is running. Keep children away from the machine. Keep hands and feet away from the machine and its moving parts.

6.       Do not fill the tank while the engine is moving.

7.       Keep all flammable materials (including dry straw) away from the engine.

8.       Do not oil, grease, or adjust the machine during operation. Wait until all moving parts have stopped before servicing.

9.       Do not operate machine with loose peg teeth, bolts and nuts. Loose peg teeth may be ejected at high speeds, causing injury to operators and  damage to the thresher.

10.    Never remove accumulated straw inside the machine during operation.

11.    Never extend hands or feet into the feed opening of the thresher.

12.    Never operate your machine in a closed shed or garage. Exhaust fumes are dangerous to your health.

13.    Keep a first-aid kit at hand.

14.    Tie up long hair to prevent entangling.

15.    Do not wear necklace or other garments that may be wrapped into moving parts of the machine.

          Combine Harvesting

1. Review the manuals that came with the harvester. Understand the controls before operating.
2. Do the operational check-up before operating.
3. When operating around machinery, wear work clothes that fit and have no loose ends.
4. Do not allow anyone to climb onto the machine while it is in motion.
5. Keep children at a safe distance from the machine.
6. Do not operate when very tired. Change operators during the day.
7. Always have a fire extinguisher at hand on engine-operated equipment.
8. Ensure that the fuel system has no leaks.
9. While refueling, stop the engine and do not smoke.

                 IMPORTANT THINGS TO REMEMBER

• Harvesting is the process of collecting mature rice crop from the field.
• Threshing is the process of separating rice grain from the panicle.
• The maturity indices of rice are: a) 80-85% of the grains are straw colored b) grains have 20-25% moisture content of the grain c) based on maturity date
• Methods of harvesting are manual or mechanical.
• The choice of selecting the method in threshing depends upon the availability of labor, capital outlay of the farm, time of harvesting, field layout, demand for quality, and demand for straw.
• Observe the safety measures in harvesting, threshing, and milling.
• Clean rice is easier to dry.
• Clean rice when properly dried to improve the storability.
• Clean and properly dried rice grains have higher market value.
• Clean and properly dried rice grains obtain good milling quality.
• Store rice grain for future use.
• Observe safety precautions when using chemicals, especially in the control of pests in the storage barn.
• The moisture content of rice grains for storage is 14 percent.
• Sundrying can be done 1-2 days (fair weather) or 8-11 hours if mechanical dryer is used.