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Production Know How
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Guidelines for Machine Threshing of Rice

Guidelines for good machine threshing methods/recommended practices are:

1. When to harvest: The axial-flow threshers that are particularly designed for rice can handle very wet crop. Therefore harvest the grain at optimum maturity to maximize yield and minimize losses.

2. Timing of threshing: Ideally, machine threshing should begin immediately after cutting and often these crops can be threshed in the field. Immediate threshing reduces the exposure of crop to insects, birds and rodents, disease, and molds.

3. Machine adjustments: Wrongly adjusted threshers create higher threshing loss and grain damage. Always make sure that threshing drum speed and the cleaner settings are done properly according to the crop conditions.


Machine Threshing of Rice


1. Because of high labour requirements of manual threshing, many countries threshing of paddy is now mechanized by use of small stationary machine called as threshers. Stationary threshing is generally done in the field, or near or at the field side. 2. Many stationary threshers for paddy have peg-toothed threshing drums, however threshers fitted with wire-loop or rasp-bars are used as well. Most threshers are of the feed-in type (e.g. entire crop is fed through the thresher) which ensure high throughput. 4. Hold-on threshers (only panicle is fed into the machine) generally have a lower capacity than feed-in threshers and are primarily used in areas where rice straw is bundled and stored for later use. 5.Large stationary thresher are fitted with additional cleaning devices such as an oscillating screen, centrifugal blower, and wind board, and threshed grain can be handled without further cleaning. 6. 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.

Guidelines for good Manual Threshing

1. For hand threshed crops, partial drying in the field for a couple of days may be necessary to lower the moisture content and make threshing easier.

2. The highest milling yield will be attained for hand threshed, sun dried rice at grain moisture content between 18-20%. Care must be taken not to over dry the crop if it is to be transported any distance before threshing as excessive shattering will occur.

3. While the crop may be dried before threshing, dried crop should not be subjected to rewetting. Rewetting causes grain fissures which lead to high broken grain when milled.

4. In wet crop conditions, manual threshing is difficult if crop is sufficiently dried (e.g. wet season harvest).


Threshing of Rice

 1. The common method for threshing is hand threshing. In this, the separating of grain is from the panicle is done by hand beating, treading, or by holding the crop against a rotating drum with spikes or rasp bars.

2. Hand beating methods are normally used for threshing of rice that easily shatters. Hand threshing methods include: • Foot threshing or trampling: use of bare feet to thresh the crop. To do this successfully, the crop is spread over a mat or canvass and workers trample with their feet

• Beating against a threshing rack: the farmer holds the crop by the sheaves and thrashes it against a slatted bamboo or wooden platform

• Flail: the use of a flail or stick for thrashing the crop

• Using a pedal thresher or treadle thresher.

3. The another traditional method is use of animals to thresh the grain. Animal threshing is normally carried out at a designated location near the field or in the village. In some regions, animals have been replaced by tractors. After animal treading, cleaning of the grain is done by winnowing, with or without the aid of an electric fan.

4. The pedal thresher or treadle thresher consists of threshing drum, base, transmission unit and a foot crank. When pedalled, the threshing drum rotates and rice can be threshed when panicles are applied against the threshing drum. Because small straws, chaff, and foreign matter drop along with the threshed grain, whole grains must be separated using a flail, sieve or by winnowing.


Harvesting of Rice Crop

  1. To harvest manually, cut the rice with a sickle either at the stems close to the ground or cut just the panicle. 2. Manual harvesting system is most common in India. It includes the rice crop is cut with simple hand sickle 10-15 cm above the ground level. 3. After harvesting the rice crop put together in bundles and left on the field itself for drying for easy threshing. 4. For harvesting of rice crop require 40-80 man hours per ha. 5. Rice cutting is also done by using mechanical reapers. But for cutting the crop with reapers the field should be levelled. A reaper with a cutting-width of 1.5 m can operate at a rate of 2 to 4 ha per day.


Time of Harvesting of Rice Crop

 1. Taking the average duration of the crop as an indication, drain the water from the field 7 to 10 days before the expected harvest date as draining hastens maturity and improves harvesting conditions.

2. When 80% of the panicles turn straw colour, the crop is ready for harvest. Even at this stage, the leaves of some of the varieties may remain green.

3. Confirm maturity by selecting the most mature tiller and dehusk a few grains. If the rice is clear and firm, it is in hard dough stage.

4. When most of the grains at the base of the panicle in the selected tiller are in a hard dough stage, the crop is ready for harvest. At this stage harvest the crop, thresh and winnow the grains.

5. Dry the grains to 12% moisture level for storage. Grain yield in rice is estimated only at 14% moisture for any comparison.

6. Maturity may be hastened by 3-4 days by spraying 20% NaCl a week before harvest to escape monsoon rains.


Choosing an appropriate system for harvesting

 In India the most common harvesting systems are: 1. Manual system using manually operated tools: This includes use of traditional tools for threshing such as threshing racks, simple treadle threshers and animals for trampling. A pedal thresher is a simple tool to improve manual threshing.

2. Manual harvesting followed by machine threshing: The use of portable thresher is usually the first step in mechanical harvesting.

3. Mechanized cutting followed by machine threshing: Cutting and laying the crop on a windrow is done using a reaper, threshing by a thresher and cleaning either manually or by machine.

4. Combine harvesting: The combine harvester combines all operations: cutting, handling, threshing, and cleaning.


When to Harvest Rice Crop

1. Harvest paddy rice at the right moisture content (20-25%).

2. At maturity, about 80% of the grains turn yellow whilst part of the stems and leaves remains green.

3. Panicle maturity normally occurs at about 28-34 days after heading.

4. Timely harvest will reduce yield loss due to:

• Grain shattering.

• Cracking of grains in the field and grain breakage during milling.

• Lodging and grain discolouration, under wet weather.

• Birds and rodent attack.

5. In the north, delayed harvest may result in complete field loss through bush fire.


Harvesting and Threshing

1. Harvesting is an operation of cutting, picking, plucking, digging or combination of these for removing the useful part or economic end product, part from the plant.

2. Threshing is the process of separating the grain from the straw. It can be either done by hand, by using a treadle thresher or by using a machine.

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