Rice harvesting

When to harvest

Harvest at the right time is important because;

1. maximize grain yield, and 2. minimize grain damage and quality deterioration3. maintains the germination potential of rice seed

Harvesting

too earlyHarvesting rice earlier will result in a larger percentage of unfilled or immature grains, which results in lower yield and grain quality. Lower grain quality may lead to higher grain breakage during milling. If the grain has a moisture content > 25% , it is more difficult to remove the grains from the panicle and some damage may occur during machine threshing.

Harvesting

too latebeyond optimum maturity can lead to a rapid reduction in moisture content to <20%, which is too dry for mechanical harvest. This can lead to high shattering losses. Grains that dry during the day might absorb moisture during night or during rainfall resulting in cracks, which reduces the milling yield. In addition, grains become more brittle and therefore break easier in the thresher.

The right harvesting time

As a guideline, harvest can be based on

1. Measuring moisture content (M.C.) Measuring MC is the most accurate

method. For harvesting the grain moisture content ideally is between 20-25% (wet basis). Grains should be firm but not brittle when squeezed between the teeth.

harvesting time …cont

2. Ripe grains per panicleThe crop should be cut when 80-85% of the grains are straw colored.

harvesting time …cont

3. Number of days after sowingGenerally the ideal harvest time lies between;

Late variety = 130-136 days after sowing , Medium variety = 113- 125 days, and

Early maturing varieties 110 days

harvesting time …cont

4. Number of days after headingGenerally the ideal harvest time lies between;

In dry season harvest, an optimum time of harvest is 28 to 35 days after heading.

In wet season harvest, optimum time is 32 to 38 days after heading.

Harvesting operations

• Cutting

• Hauling

• Trashing

• Cleaning

Harvesting systems

1. Manual system using manually operated tools

Harvesting systems

2. Manual harvesting followed by machine threshing

Harvesting systems

3. Mechanized cutting followed by machine threshing

Harvesting systems

5. Combine harvesting

Drying rice

Rice dryingwhy drying rice grains ?

Any questions

The rice grain quality

Components of grain quality;Moisture content.Purity: dockage and varietal.Cracked grainsImmature grainsDamaged grainsDiscolored/fermented grains

Grain moisture content

Irrigated 55%Rainfed lowland 25%

Paddy is at its optimum milling potential at moisture content of 14% wet weight basis

Purity

1. Dockage.refers to materials other than paddy and includes chaff, stones, weed seeds, soil, rice straw, stalks, etc

Purity…cont

2. Varietal A mixture of varieties causes difficulties

at milling, thus lower grade of milled rice.

Cracked, immature and damaged grains

1. Cracked. Overexposure of mature paddy to fluctuating temperature and moisture conditions leads to development of fissures and cracks in individual kernel. Cracks in the kernel are the most important factor contributing to rice breakage during milling.

Cracked, immature and damaged grains

2. Immature Affect yield and quality.

The optimal stage to harvest grain is at about 20-24% grain moisture or about

30 days after flowering

…..cont

3. Damaged development of off-odours and changes

in physical appearance. These types of damage are caused from water, insects, and heat exposure.

Discoloration/fermented grains

over-exposure of paddy to wet environmental conditions before it is dried. This results in a combination of microbiological and chemical activity that overheats the grain

Any questions

Rice storage

Tips on storage

Safe storage of rice for longer periods is possible if three conditions are met:

• Grain is maintained at moisture levels of <13% or less

• Grain is protected from insects, rodents and birds

• Grain is protected from re-wetting by rain or imbibing moisture from the surrounding air.

Seed moisture during storage

Seed is hygroscopic .If seed moisture >13% problem with insect and

fungi damage in storage.Therefore, moisture of 9-12% must be maintained.

For very long storage, very low moisture <8% , hermetic storage is practice, in air tight bottle.

Thank you