Sunday, 21 December 2014

Rice Harvesting

Harvesting is the process of collecting the mature rice crop from the field. Paddy harvesting activities include cutting, stacking, handling, threshing, cleaning, and hauling.These can be done individually or a combine harvester can be used to perform the operations simultaneously.
It is important to apply good harvesting methods to be able to maximize grain yield, and minimize grain damage and quality deterioration.

When to harvest

Depending on the growth duration of the variety, harvesting time should be around 110−120 DAS for direct seeded rice, and 100−110 DAT for transplanted rice. 
The following are indicators for harvest:
  • Moisture content
    Grain moisture content ideally is between 20 and 25% (wet basis). Grains should be firm but not brittle when squeezed between the teeth.
    Harvest at minimal surface moisture (e.g. from previous rainfall or early morning dew).
  • Ripe grains per panicle
    The crop should be cut when 80−85% of the grains are straw colored (i.e., yellow-colored).
  • Number of days after sowing
    Generally the ideal harvest time lies between 130 and 136 days after sowing for late-maturing variety, 113 and 125 for medium duration, and 110 days for early-maturing varieties.
  • Number of days after heading
    For dry season harvesting, an optimum time is 28 to 35 days after heading (emergence of panicle tip from leaf sheath). In wet season harvest, optimum time is 32 to 38 days after heading.

Guidelines

Harvesting can be done manually using sickles and knives, or mechanically with the use of threshers or combine harvesters.
Regardless of the method, it is important to ensure that good grain quality is preserved during harvest operations and harvest losses are kept to minimum.
The following are guidelines to proper harvesting:
  1. Harvest at the right time with the right moisture content
    • Correct timing is crucial to prevent losses and ensure good grain quality and high market value. Grain losses may be caused by rats, birds, insects, lodging, and shattering.
    • Harvesting too early results in a larger percentage of unfilled or immature grains, which lowers yield and causes higher grain breakage during milling.
    • Harvesting too late leads to excessive losses and increased breakage in rice.
    • Harvest time also affects the germination potential of seed.
  2. Avoid delays in threshing after harvesting
    • Time harvesting so threshing can be done as soon as possible after cutting to avoid rewetting and to reduce grain breakage.
  3. Use proper machine settings when using a threshing machine
  4. Clean the grains properly after threshing
  5. Dry the grains immediately after threshing

Harvesting systems

Various harvesting systems can be observed in different locations. These include different methods and machines used for mechanizing the harvesting operations like cutting, threshing, and cleaning.
In Asia, the most common harvesting systems are:
  • Manual harvesting and threshing
    This includes use of traditional tools for harvesting (sickles, knives) and threshing such as threshing racks, simple treadle threshers and animals for trampling. A pedal thresher is a simple tool to improve manual threshing.
  • Manual harvesting and mechanical threshing
    The use of portable thresher is usually the first step in mechanical threshing. The use of small stationary machine threshers commonly replaces manual threshing given its high labor requirements. Stationary threshing is generally done in the field, or near the field.
  •  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.
  • Combine harvesting
     The combine harvester combines all operations: cutting the crop, feeding it into threshing mechanism, threshing, cleaning, and discharge of grain into a bulk wagon or directly into a bags. Straw is usually discharged behind the combine in a windrow.
Choosing an appropriate harvesting system depends on a number of factors:
  • Availability of labor (harvesting is labor intensive)
  • Capital outlay of the farm 
  • Timeliness of harvesting (how much time is available to complete the harvest)
  • Field layout and field accessibility (combine harvesters require a certain field layout and access)
  • Rice Variety (some varieties are more prone to lodging)
  • Demand for quality rice
  • Demand for straw (certain threshers damage the straw making it less marketable)

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