Project Completion Report:" Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam - MS4 " docx

180 Ministry of Agriculture & Rural Development Project Completion Report MS14: PROJECT COMPLETION REPORT 026/05VIE Investigation of rice kernel cracking and its control in the field

180

Ministry of Agriculture & Rural Development

Project Completion Report MS14: PROJECT COMPLETION REPORT

026/05VIE

Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the Mekong Delta of Vietnam

APPENDIX 8A

EXTENSION WORKERS MANUAL-PART 1

IMPROVING FARMER’S PROFITABILITY BY MINIMIZING GRAIN LOSS AND MAINTAINING QUALITY THROUGH

CORRECT PROCEDURES DURING HARVESTING AND

POST-HARVEST OPERATIONS

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INTRODUCTION

Reduced whole rice grain yield and value due to cracking is one of the major issues that directly reduce income and availability of staple food to the farmers in the Mekong River Delta The cracking or partial fissuring of rice kernels may occur right in the paddy field due to incorrect harvesting time/practice, improper post-harvest drying conditions and inappropriate milling operations

There is a chain of activities during harvesting and post-harvest processing of rice Figure 1 is a diagram showing a post-production system of rice in the MRD of Vietnam currently All chains in this system can contribute to losses Some of the important factors can be dependent to each other Here we consider two aspects:

1 Grain loss (G): Harvesting and post-harvesting losses in which grain is not fully recovered during a

particular operation on farm

2 Value loss (V): Grain cracking and reduced head rice yield which result in downgrade in grain

quality value, such as broken rice during milling The value of rice might be reduced by 50% or less

Accordingly, the manual is divided into 4 sections in relation to:

The main factors which contribute to the rice cracking and value losses are:

• Harvesting time- before and after grain maturity

• Harvesting methods- manual, reaper, combined harvester

• Drying methods- sun drying and mechanical drying

• Milling losses- small, medium, large rice milling plants and milling procedure

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Types of Losses

Harvesting

Method Manual cutting + Hand collecting + Mechanical Threshing

Reaper + Combined-Collector (collecting + threshing)

Figure 1: Post-production system of rice in the Mekong River Delta of Vietnam and loss

components G is grain loss, V is value loss, *, ** and *** signs indicate relative degree of losses

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SUMMARY OF POST-HARVEST LOSSES

Table 2 is the summary of total post-harvest losses (Table 2) based on the data collected in the past two years from Mekong Delta region In this table, the values are the overall estimation from different varieties The values presented are in the relative term between the cases For instance, late harvesting has 3.5% of losses in comparison to harvesting at correct time The value loss at correct harvesting time

Table 2: Overall evaluation of total post – harvest losses (late harvesting, moderate milling quality)

Harvesting

time

Harvesting method Threshing Sun drying Drying Milling

Total (%)

Yes (V=1.5%)

V = 1.5%)

No (0%)

Incorrect (V=5%)

Good quality (0%)

Yes (V=1.5%)

V = 1.5%)

No (0%)

Incorrect (V=5%)

Average quality (4%)

15.2 Note: V= Value losses, G = Grain losses

There are three cases of losses that can be highlighted in Table 2

1 The highest total losses is 20.6% including late harvesting (3.5%), manual cutting (2.9%), threshing (1.5%), field drying (8.7%), incorrect drying procedure (5%) and using average milling quality (4%)

2 The common cases of total losses are in the range of 12.4 to 15.9% including correct (or late) harvesting time, manual cutting, threshing, sun drying on yard, average milling quality applied

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1 INFLUENCE OF HARVESTING TIME ON THE RICE

CRACKING AND QUALITY LOSSES

Physical grain losses during harvesting can be divided into various types, depending on the operation and the machinery used

Losses during cutting crops

• Shattering loss: shedding of mature grains from the panicle caused by birds, wind, rats, and handling

• Lodging loss: plants with mature grains fall on the ground making the grains difficult to recover

• Standing crop loss: standing plants with mature grains are left standing in the field after harvesting

Losses during threshing and cleaning

• Separation loss or “blower loss”: grains that are mixed with straw or chaff during the cleaning operation

• Scatter loss: grains that are scattered on the ground during the threshing and cleaning operation

• Threshing loss or unseparated loss: mature grains that remain attached to the panicle in the straw after completion of

the threshing operation

Losses during crop and grain handling:

• Handling loss: mature grain lost during lifting, hauling, stacking, pouring, and bagging of crop and grains

Incorrect time of harvesting increases harvest losses The main problem is caused by delayed harvesting, as this increases susceptibility to shattering, lodging and standing crop losses

Incorrect harvesting time is also one of the major factors that cause the losses due to cracking Cracking can develop in the field as a result of changes in grain moisture or moisture cycles after the rice matures due to hot sunny days followed by humid nights The cracking behaviour of the rice in the field is expected to depend on the season due to the different patterns of temperature fluctuation during day and night, degree and strength of sunshine and frequency of rain During the rainy season, the rice grain can develop cracks during the late maturity stage due to rewetting At the same time, during dry season it is likely that the grains over-dry if not harvested at correct time Thus we need to identify the correct time for harvesting

Estimating the correct time of harvesting

Recommended time of harvesting for each variety is estimated from the time of sowing in each season Table 3 presents the estimated days from sowing to harvest for various varieties in MRD

When the crop approaches the estimated optimum time of harvesting, then further observation is made

to determine the exact time of harvesting 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 However,

in the Summer-Autumn season in Mekong Delta River, the moisture content is normally 28-30% due to frequent rains This means that prompt drying of grain is very critical to avoid rice cracking, germination and fungal damage

At around this time, the crop should be cut when 80-85% of the grains are straw (i.e yellow) coloured (see photograph)

Harvesting also needs to be timed so that threshing can be done as soon as possible after cutting to avoid re-wetting and reduce grain breakage Thus, combine-harvester is the best harvesting method

If the crop has a lot of surface moisture, e.g from previous rainfall or early in the morning, it is advisable to wait to cut the crop until the surface moisture dries off

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From the experiments on 7 rice varieties in three seasons in the past 2 years (2006-2008), the optimal harvesting time to maximise head rice yield for each variety in each season (dry/rainy) is presented in Table 4 Most of the cases fell within the recommended day mentioned in Table 3 However, some cases were outside of this range such as OM2517 (94 days in rainy season), AG24 (94 days in rainy season) and OM2718 (88 days in rainy season)

Table 4: Optimal growing time for highest HRY (coloured numbers are the optimal growing time for harvesting)

Harvesting too early will result in a larger percentage of unfilled or immature grains, which will result

in a lower yield and in higher grain breakage during milling

Harvesting too late will lead to excessive losses and increased breakage in rice

Grain cracking and head rice yield (HRY)

The following figures (Figure 2 and 3) show the mean of grain cracking and also that of head rice yield among several varieties obtained in Mekong Delta during 4 seasons of experiments in 2006-2008

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51.06 52.3 50.73

47.99 42.23 36.51 34.53

0 5 10 15 20 25 30 35 40 45 50 55

0 2 4 6 8 10 12

-6 -4 -2 0 +2 +4 +6 Harvesting time (days from maturity)

Figure 2: Effect of harvesting time on grain cracking

The X axis indicates days of early or late harvesting compared to maturity date (day 0)

Figure 3: Effects of harvesting time on head rice yield

The X axis indicates days of early or late harvesting compared to maturity date (day 0)

Do Not harvest late after the maturity date in order to avoid cracking and to increase HRY

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Table 5 summarises the losses due to late harvesting for different varieties harvested in different seasons of MRD in 2006-2008 The HRY is reduced by 5-28% if harvesting time was 6 days late Assuming 1% of HRY reduction equivalent to 0.5% of losses (50% value loss), then late harvesting would cause a loss of 2.5-14% The varieties AG24 and IR50404 had losses below 2.5%, whereas the varieties OM1490, OM2517 and OM2718 had high losses of above 5% (6 days late harvesting) Theses varieties need to be harvested earlier

Table 5: Losses of Head Rice Yield (HRY %) due to late or early harvesting

Variety Season Losses of HRY (%) in comparison to optimal harvesting time

Dry/Rainy?? 0 1.57 4.31 10.07 15.79 17.77 OM1490 Rainy/Dry?? 1.69 0.97 0 3.33 7.65 11.55

Rainy 0 7.93 7.56 12.71 14.64 10.75

Rainy 5.08 11.36 7.05 4.77 0 4.9 OM2517

Rainy 4.65 6.59 3.07 4.55 0 7.07 OM4498

Jasmine Rainy 0.71 3.54 0 0.77 7.21 6.2

AG 24 Rainy 6.23 4.48 3.49 0.66 0 4.27

IR50404 Rainy -0.25 0.89 0 5.97 1.29 2.16

Note: 0 is the optimal day After (before) this day is late (early) harvesting From one cell to the adjacent cell the harvesting

time changed by two days

The survey data shows that most of the farmers were late harvesting by 1 to 3 days For varieties, OM1490, OM2718, Jasmine and AG24 were harvested late by 80%, 90%, 55% and 50% of farmers, respectively

1 The harvesting time is one of the important factors to control the rice cracking and eventual head rice recovery There is a clear trend that a few days early harvesting (before maturity) is better than the late harvesting

2 The same effect persists in rainy or dry season (check further data – more figures have been inserted to Figure 2 &3)

3 Varieties differ in their grain cracking and those with small cracking such as AG24 is recommended When head rice recovery is also considered, OM4498 had smaller loss even it

Field experiments indicated

that: 4-6 days late harvesting

increase cracking by up to

24%, and reduce HRY by up to 28%.

In addition, the farmers are encouraged to plant varieties with different maturities so that each crop can be harvested at the correct time of harvesting There may also be some opportunities to plant at different times of the same variety, so that the harvesting is spread for a longer time period However, the best option is to introduce mechanical harvesting (see Section 2)

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2 INFLUENCE OF HARVESTING METHOD ON THE RICE

CRACKING AND QUALITY LOSSES

Harvesting systems vary from region to region and include different methods for harvesting, hauling, threshing and cleaning The goal of good harvesting is to ensure maximum grain yield through minimizing grain loss and the prevention of quality deterioration, including cracking

A wide variety of harvesting tools is used, such as knives, sickles, animals, stationary threshing machines, tractor-mounted harvesters, and self-propelled combine harvesters In Vietnam including Mekong River Delta, the most common systems for paddy harvesting are:

1 Manual harvesting, collecting by hand, followed by machine threshing (no more manual threshing in Vietnam)

Manual cutting Manual collecting Machine threshing

2 Harvesting by reaper, manual collecting followed by machine threshing

Cutting by reaper Manual collecting Machine threshing

A lot of labours are required for manual collecting after harvesting by reaper

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3 Machine harvesting with a reaper, followed by combined collection-threshing

Cutting by reaper Combined collection and harvesting

Cutting and laying the crop on a windrow is done using a reaper, followed by collection and threshing using a machine

4 Combine harvesting

The combine harvester combines all operations: cutting, handling, threshing and cleaning

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Table 6: Advantages, disadvantages of the applied harvesting methods used in the Mekong Delta

Multi-step harvesting:

+ Manual harvesting, field drying,

piling and threshing

- Cut rice stem is short reducing threshing energy

- Field drying reduces energy for drying and threshing

- Independent to soil condition and the degree of lodged rice

- High cleanness of rice

- Low capacity, require a large number

Dependency on availability of contractor

Piling: a hard work

The grain germinated

20 hours after harvesting due to wetting in the rain (Spring-Summer)

+ Harvesting by reaper, field

drying, piling, threshing

- The machine is not heavy, high capacity (1-6 ha/day); it can work

in the soft soil field

- The strength of reaper is moderate and rarely damaged seriously The spare parts are available locally

- High cleanness of rice

- High mobility

- Moderate investment

- High amount of rice stem (2-3 times compared to manual harvesting) increased time and energy for piling and threshing; it’s hard to harvest lodged rice This is the major disadvantage of the reaper

- High losses during harvesting and piling over-matured rice

- Grain quality is not as good as in the case of manual harvesting if field drying is applied

Harvesting by reaper, combine-

collection and threshing

- The reaper machine is not heavy, high capacity (1-6 ha/day); it can work in the soft soil field

- The combine- collecting and threshing machine can work in soft soil field where heavy combine harvester could not work

- High capacity, less labours requirement

- Higher capital cost

- More straw left behind in the field

- The mobility of the machine in the field depends on the weight of machine and the size of field

One step harvesting:

- The mobility of the machine in the field depends on the weight of machine and the size of field

- Hard to harvest lodged rice

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- Grain quality good - The machine consists of many parts

and elements which lead to complex operation and maintenance

- Degree of cleanness is not high when grain moisture is high

- The mobility is not high where the chain is used

The investment cost is high

Estimated harvesting losses

Harvesting losses consist of shattering and threshing losses Table 7 shows each component and total

harvesting losses The total harvesting losses can be as high as 4.4% A threshing loss of 1.0% for

combine harvester was estimated by the manufacturer On an average, mechanical harvesting reduces

harvesting losses

Table 7: Effect of harvesting methods on the harvesting losses

Harvesting method Shattering

losses (%)

Threshing losses (%)

Harvesting losses (%)

Hand Hand and dried in the sun (one

day)

1.2-3.0

1.2 2.4-4.2 Reaper and heaped

The information shown above is for the case when crops are harvested at a correct time Due to longer

time required for harvesting, it is likely that manual harvesting will result in greater delay in harvesting

time, and hence greater harvest losses

Thus,

• Shattering loss due to harvesting method and also due to time of harvesting (particularly late

harvesting) is an important factor to consider for reduction in the grain losses during harvesting

• Machine harvesting is beneficial in terms of quick harvesting of the crop and hence in terms of

minimizing harvesting losses

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Grain cracking and head rice yield (HRY)

Effect of harvesting method

Harvesting method as such may not affect grain cracking and head rice recovery (Check), but manual

harvesting often results in delayed harvesting, and this can cause grain cracking and reduced head rice

recovery Thus, when harvesting is to conducted to be manually, it is important to time the operation so

that crops can be harvested at correct time

In addition, manual harvesting results in higher scattering losses in comparison to machine harvesting

Data collected from some farmers who harvested manually are presented in Table 8

Table 8: Scattering losses in the field of different farmers harvested manually

Farmer Rice

variety

Initial rice moisture (before harvesting) (% wb)

Moisture content of rice during threshing (% wb)

Number

of kernels scattered per 25m2(g)

Productivity (kg/1000m2)

% losses

Effect of threshing method on grain cracking and head rice recovery

The threshing method applied can cause the cracking in the rice kernels and eventually reduce the head rice

recovery The data collected in two provinces in Mekong Delta at the same time when experiments were

conducted are presented in Table 9 The results indicate that the grain cracking is not significantly affected by

the method of threshing However, some reduction of head rice recovery was observed in the case of rice

threshed by machine

Table 9: Effect of threshing method on rice cracking and head rice recovery

Grain cracking (%) Brown rice White rice

Head rice recovery (%)

195

Ministry of Agriculture & Rural Development

Project Completion Report

MS14: PROJECT COMPLETION REPORT

IMPROVING FARMER’S PROFITABILITY BY MINIMIZING GRAIN LOSS AND MAINTAINING QUALITY THROUGH CORRECT PROCEDURES DURING HARVESTING AND POST-HARVEST

OPERATIONS

196

3 EFFECT OF DRYING METHODS ON RICE

CRACKING AND HEAD RICE RECOVERY

Importance of drying

Drying is the process of removing water from the grains to reach safe storage moisture content (MC) Rice is harvested at grain moisture content between 20 and 30% (wet basis), depending on the season of harvest Failure to dry the rice often results in its deterioration due to micro-organisms and discolouration Depending on the desired storage period there are different recommended moisture contents for safe storage (Table 10)

Table 10: Safe storage period of rice at different moisture content

Storage period Desired moisture content

8 to 12 months 13% or less Insect damage

More than 1 year 9 % or less Loss of viability

Delays in drying, incomplete drying or uneven drying will result in qualitative and quantitative losses including:

• Yellowing or discoloration caused by mold development and heat build-up from respiration

• Development of rice cracks with eventual reduced milling yields caused by high temperatures and re-wetting of grains

• Loss of germination and vigor caused by grain respiration, mold and insect activities, or from exposure of grains to temperatures above 42ºC

• Damage caused by insects that are more active at higher moisture levels

Principles of drying

Drying of grains involves exposing grains to ambient air with low relative humidity or

to heated air or to the sun The moisture evaporates from the grain and then the drying

or ambient air removes the moisture from around the surface of grain

Drying methods

After harvesting (cutting in the field) the rice lots are dried by different methods:

Field drying is practiced prior to threshing when hand or reaper is used for cutting the

rice The drying rate will highly dependent on the weather condition and the stage of

harvesting There are losses due to shattering of the grain and rice cracking due to

over drying or rewetting of the grain, if the rice is not threshed in time The major

disadvantages of this method are:

ƒ Rewetting from straw or soil which can cause rice

cracking and high proportion of broken rice during

milling

ƒ Rewetting during night time due to high humidity

resulting in grain cracking and low milling yield

ƒ Non-uniform drying due to uneven spreading of the

stack Grains outside will dry faster than the inside

the stack

The experimental results presented in Table 11 indicate that there will be reduced

head rice yield due to field and sun drying

Table 11: Loss of head rice yield (HRY) in equivalent to losses of paddy (kg/100

kg yield) for different varieties in the Mekong Delta due to current practices of

field and sun drying

Variety OM1490 OM2718 Jasmine AG24 Loss of head rice yield (%) 7.32 8.97 10.45 7.87

Sun drying

Sun drying is the common drying method practiced by farmers in Vietnam including

Mekong Delta In this method, the rice grains are spread under the sun after threshing

operation The rice is normally spread on the concrete, asphalt or plastics It is a low

cost but labour intensive drying The control of grain temperature is difficult The top

layer of the rice bed will heat more than the interior of the bed Regular mixing is

practiced to minimise the temperature and moisture differences between the layers of

bed

Sun drying has some limitations:

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• Not possible during rain and at night Any delay leads to excess respiration and fungal growth causing losses and yellowing

• Labor intensive and has limited capacity

• Overheating causes cracking of some grains and result in low milling quality

• Mixing operation is labour intensive and is difficult to handle in large

amounts

Table 12: Milling losses (head rice yield reduction) due to sun drying as

compared to artificial drying (in dry season)

Head Rice Yield, %

Variety In shade drying

(controlled

sample)

Mechanical drying (Flat-bed dryer)

Sun drying (Plastic, Ts = 42-48oC)

HRY reduction due

49.6 49.1 50.7 51.3

47.5 45.3 44.6 48.2

2.1 3.8 6.0 3.1

Note: Ts is the grain surface temperature

On average, losses due to field and sun drying were found around 8.7% (Table 11) This loss

is for winter-spring season The losses in the wet season (Summer-Autumn crop, July/August) are expected to be much higher due to changeable weather of rain and storm

Artificial drying

Artificial drying is used to dry the grain faster than the traditional method in a control condition The artificial drying is better than sun drying in terms of grain quality and milling yield In this method the drying air is blown across or over the bed of grain to drive moisture out from the grain The drying temperature and conditions are correctly selected in order to avoid the grain cracking

There are low, medium and high temperature dryers The low temperature dryers use below <35oC (or just use ambient air if the humidity of the air is low enough) Low temperature drying is very slow process but it is gentle enough to minimise rice cracking during water removal due to low moisture differential in the grain at a given time However, this is not economical because the drying rate is very slow Medium temperature dryer may use 35-50oC drying air temperature This is the most practiced condition, but it can cause grain cracking if the drying temperature condition is not properly controlled High temperature dryer may use above 60oC High temperature drying can cause rice cracking resulting from the moisture driven mechanical stress due to faster drying from the exterior surface of the grain than from the interior

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Therefore, an additional intermittent tempering process is necessary to allow moisture

to equilibrate from interior to exterior and reduce the differential moisture

There are various types of dryers are used

Bin drying

This is a low temperature drying method Paddy with moisture

content already below 18% can be slowly dried in storage bins

using aeration with slightly pre-heated air Since there is not

mixing of the grain involved, the grains close to the air entry

point will dry faster than the interior Some cracking of grain

may occur at the entry point if the temperature is a bit high and

the humidity of the air is very low This type of drying method is

not a common practice in Mekong River Delta

Flat bed drying (FBD)

This is the most common dryer found in Mekong

delta Flat bed driers are also called fixed-bed dryer

In this dryer the heated air is forced through the bulk

grain The grain is kept stationary in a holding bin

until drying is completed The dryer capacity is

flexible, can range from 1 to 10 tons 10 ton/batch is

the maximum size in terms of labor management On

average drying time is 7-10 hrs depending on the

initial moisture content Bed configurations of

fixed-bed batch dryers can either be rectangular (flat-fixed-bed

dryer), inclined for better unloading or circular The

recommended drying temperature is 43-45oC

Figure 1: 8-ton flat bed drier Fixed-bed batch dryers produce better grain quality than sun-drying They are more affordable than re-circulating batch dryers of the same capacity or continuous flow dryers and have certain advantages:

• Easy to operate

• Simple design allows local production of the drying bin, blower and furnace and ensures easy maintenance and repair

• Heating system (furnace) usually uses rice husk as fuel

• The air blower can be operated with a gasoline or diesel engine in areas where electricity is not available or too expensive

• The same dryer can be used for other grains such as corn

Some important points to remember while operating flat bed dryers (FBD)

• Load the drying bin evenly If some lots of rice contain different moisture content, mix all before drying

• For seeds don’t exceed 43°C drying air temperature

• Increasing the temperature reduces drying time but increases uneven drying and can cause rice cracking

• Increasing the airflow shortens drying and reduces the moisture content but increases energy cost

• Mixing during drying reduces the moisture gradient

Schematic diagram of furnace

Rice husk furnace with cylindrical ash collector Automatic rice husk furnace

Due to the large depth of the grain and drying passing though one end, there is a difference in moisture content between the bottom and the top bed Mixing reduces this difference, but the mixing can not be efficient and is labour intensive In order to simplify, a reversible air flow

is used after certain period of drying

Figure 2: 1-ton reversible dryer

Drying Air UP

Grain

CONVENTIONAL SHG FLAT-BED DRYER Floor: 50 sq.m / 8 ton

0.3m