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

Effect of harvesting time on the rice cracking and head rice yield Incorrect harvesting time is one of the major factors that cause the losses due to cracking.. 1.1 Harvesting time and

Ministry of Agriculture & Rural Development

Project Progress Report

026/VIE05 Investigation of rice kernel cracking and its control in the field and during post-harvest processes in the

Mekong Delta of Vietnam

MS4: BASE LINE INFORMATION

Dr Vinh Truong, Nong Lam University

Associate Professor Bhesh Bhandari and Professor Shu Fukai

The University of Queensland

May 2007

BASE LINE INFORMATION

In order to determine the actual post harvest losses mainly due to rice cracking, the

baseline data was collected systematically based on the farmers practice and also by

experimentations There is a chain of activities during harvesting and post-harvest

processing of rice Each of these factors will contribute to the losses Some of these

factors can be dependent to each other The main factors which were considered in this

study during the collection of data were:

• 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

The behaviour of the rice grain to cracking will depend on the variety and the season

Considering this factor the data were collected for 6 different varieties in 4 different

locations of Mekong River Delta (MRD) The information presented here in this report is

only for rainy season rice crop (harvesting season June/July) Collection of more data will

continue for dry season crop (harvesting season February/March)

The survey data from farmers was collected during the winter-spring season for the same

varieties The experimental data for the winter-spring season will be presented in the

forthcoming report

1 Effect of harvesting time on the rice cracking and head rice yield

Incorrect harvesting time is 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 The objective of this experiment was to

determine the effect of harvesting time on kernel cracking of some rice varieties in rainy

season in the MRD

Harvesting time field experiments were conducted in the three locations on four most

cultivated rice varieties in those areas (Table 1)

Table 1: Base line data collection to determine the losses due to current harvesting

practices (harvesting time and methods)

period

1 Tan Thoi 1 cooperative, Can OM 2718, OM1490 30thMay-13th June

Tho province

2 Tan Phat A cooperative,

Kien Giang province

An Giang 24 (AG24) 22nd-30th July

3 Seed centre, An Giang

province

Jasmine June/July

According to local survey results, the one or two most cultivated rice varieties OM 2718

and OM 1490, An Giang 24 and Jasmine were chosen in Can Tho, Kien Giang and An

Giang provinces, respectively Using a randomised block design, the rice was harvested 6

days prior and 6 days post-maturity stages in 2 days intervals for OM 2718 and OM 1490

(Can Tho) and 1 day interval for An Giang 24 and Jasmine varieties The percentage of

rice grains with cracks and head rice recovery in a laboratory milling system were

measured for both brown and white rices

The full details including the experimental design will be included in next six-monthly

report

1.1 Harvesting time and rice cracking

Some selected data on the amount of cracked grains as influenced by the early or late

harvesting from the day of maturity are presented in Figures 1 and 2 The maturity day is

taken as an estimate from farmers experience and available data from the extension office

This value was 90 days for OM 1490, OM 2718 and An Giang 24 and 98 days for

Jasmine rice varieties The head rice recovery was analysed for both brown (after

dehulling) and white (after whitening) rices

1.1.1 Cracking in brown rice and head rice recovery

Experiments conducted on four common rice varieties in three different locations indicated that the rice cracking is obviously influenced by both the variety and time of

harvesting Harvesting the rice a few days prior to maturity will not have much impact on

rice cracking, but delayed harvesting will result in significant rice cracking (up to 24% of

total brown rice) depending on the variety Interestingly, early harvesting has shown

lesser proportion of grain cracks and higher head rice recoveries This indicates how

important it is to harvest the rice in time Any over-drying in the field (or in the plant) can

result in increased number of cracked grains and reduced head rice recovery

Our results indicate that there is a varietal difference on rice cracking It should be noted

that the maturity or optimum harvesting time was an estimate which was almost the same

day for all varieties used in this investigation If varieties were harvested about the same

time, then we could conclude that 1 varieties differ considerably in the cracking (hence

intervention opportunity of growing low cracking varieties such as AG24 for farmers and

developing such varieties for rice breeders), 2 harvesting optimum harvest time had

rather small cracking problem but delay of 6 days can cause major problem (and hence

intervention opportunity), for which economic analysis can be made 3 varieties differ in

their response to time of harvesting hence time of harvesting is more critical for some

varieties than others, and hence opportunity for intervention (recommendation would be

to ensure quick harvesting for particular varieties)

3.20

9.60 4.80 10.80 15.20

0 2 4 6 8 10 12

1.73 5.47

0 2 4 6 8 10

Variety: An Giang 24 Variety: Jasmine

Figure 1: Proportion of cracked brown rice grains as influenced by harvesting time, 4-6

days earlier (-6 days) and 4-6 days later (+ 6 days) than the predicted day of maturity

1.1.2 Cracking in white rice

The cracking in the whole white rice kernels were also measured for the same rice variety samples which were used to determine the brown rice cracking It is important to know the level of cracking in the white rice because this will also be important when rice breakage occurs during post-milling conditions There is a possibility of split of the grains with severe cracks during storage, particularly if there is moisture and temperature variations or stresses This is the area which will need more investigation (although may not fall under the scope of this current project)

The cracked grains were more in the case of white rice than those in brown rice samples This is because the proportion of cracked grains is calculated based on the whole white rice kernels, excluding the broken rice The weak and fissured brown rice would normally break during the whitening process The cracking in the white rice kernels can be developed due to the shear during the whitening process Some of the brown rice kernels with minor fissures or cracks may not break during the whitening process The varietal difference on the cracking and head rice yield is obvious in Figure 2

4.40 6.00

0 2 4 6 8 10 12

1.73 4.13

Figure 2: Proportion of cracked white rice grains as influenced by harvesting time, 4-6

days earlier (-6 days) and 4-6 days later (+ 6 days) than the predicted day of maturity

1.2 Harvesting time and head rice recovery

The head rice recoveries as a function of harvesting time for four varieties of rice are presented in Figure 3 The results indicated that the head rice recovery follows the same opposite trend to rice grain cracking This obviously means that the presence of cracks in the grain influenced the head rice recovery The head rice recovery was less at late harvesting period A delay of 4-6 days reduced the head rice recovery by 7-13.4%

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

Figure 3 Influence of harvesting time on the head rice recovery of white rice

The overall results as influenced by harvesting time are presented in Table 2 It should be noted that the head rice recovery was determined by a laboratory milling system Thus, the head rice recovery will also be a function of milling efficiency Therefore, the head rice recovery data presented in Table 2 is in relative term In this case, the recovery on the harvesting at maturity (0 day) was considered as 100% In addition, due to the limited number of experiments undertaken (as feasible), the values are presented in the range The varietal factor has been incorporated within this range

Table 2: Effect of harvesting time before and after maturity (4-6 days prior and 4-6 days

later than the expected day of maturity) on the proportion of cracked grains and head rice

recovery Head rice recovery is relative to the recovery on maturity day

Proportion of cracked grain % Head rice recovery relative %

Rice variety

Before maturity After maturity Before maturity After maturity

OM1490 0.8-9.6 10.8-23.6 106-109 72-88 OM2718 0.4-1.2 2.8-10.8 104-117 84-93

Table 3: Effect of harvesting time before and after maturity (4-6 days prior and 4-6 days later than the expected day of maturity) on the proportion of cracked white rice kernels

Proportion of cracked grain % Rice variety

Before maturity After maturity

OM1490 5.2-6.1 7.2-11.6 OM2718 0.4-2.8 3.2-6.0

An Giang (24) 0.3-1.5 0.5-4.2 Jasmine 0.4-2.8 3.2-6.0

1.3 Evaluation of farmers’ practice

The farmers harvesting practice data were collected in TanPhat and TanThoi cooperatives during winter-spring harvesting season (2007) for the same varieties that were used in the experimental study Twenty to thirty farmers who had a good idea about rice harvesting and loss information participated in the survey (Annex 1) A further data collection during wet season will continue in next wet season

1.3.1 Value losses due to late harvesting:

Based on the farmers harvesting time, the potential loss incurred by farmers was

calculated from the experimental value as determined in section 1

In order to calculate the losses of head rice yield (HRY), the regression models (Table 3) were used for each variety based on the experimental data of spring-summer crop 2006/7 The losses of HRY were taken by the subtraction between HRY at the actual harvesting date and HRY at maturity date The maturity date of 90-92 was used for OM2718, OM1490 and AG24 varieties, and that of 98 was used for Jasmine variety as indicated in Table 5 The loss due to late harvesting by farmers was calculated by a regression fit of the data presented in Table 4 The value of the broken rice was considered as 50% of the whole kernel as an initial estimate A further realistic analysis will be necessary by considering various scenarios of utilisation of broken rice (such as mixing with bulk rice, sold as broken rice, sold as animal feed with our without mixing with husk or exchanged for the milling service)

Table 4: Losses of head rice yield due to late harvesting experimentally estimated for OM1490, 2718, and Jasmine varieties (using the data from Figure 3)

HRY loss= 0.0703exp(92-Growing time)+0.0699) R2=0.994

-HRY loss = 0.02414Growing time -

2.367 R2=0.743

AG24: No loss model can be estimated due to the inconsistency of HRY with harvesting time (Figure 3) It was considered that no losses at all for this variety The actual harvesting survey data from farmers also indicate that the farmers harvest the rice at early stage (Tan Phat A cooperative Kien Giang province, see appendix excel file)

For calculation of losses due to late harvesting based on the above models (as shown in the appendix), the actual harvesting time was considered to be early (late) if it was less than (more than) the maturity date collected from extension resources as shown in the below Table:

Table 5: Definition of late or early harvesting for different varieties

Variety Early harvesting

if less than (day)

Late harvesting

if more than (day)

Experimental maturity day

Maturity day mentioned by extension service OM1490

As based on the above definition, farmers normally harvest 1-3 days after the maturity date due to the lack of labour Based on our data, 80%, 90%, 55% and 50% of crop of OM1490 and OM2718, Jasmine and AG24, respectively are harvested late

The following Table 6 provides the equivalent loss data for four different varieties due to the late harvesting practice of farmers

Table 6: Losses of HRY in equivalent to losses of paddy (kg/100kg yield) for different varieties in the MRD due to current practices of late harvesting of the farmers

Variety OM1490 OM2718 Jasmine AG24

On average, losses due to late harvesting are around 2.1% These data are obtained based

on the harvesting practice of the farmers in the dry season (Winter-Spring crop, Feb/Mar) when the weather is favourable for harvesting, only the limiting factor being the labour shortage The losses due to late harvesting are not very high because most of the farmers have the knowledge of maturity day However, in the wet season (Summer-Autumn crop, July/August) the weather is changeable with rain and storm Thus, in addition to losses due to late harvesting (and field/sun drying) more losses are expected from uncontrollable bad weather

Conclusion and project intervention methods:

The following conclusion can be drawn from the above information:

• The harvesting time is one of the important factors to control the rice cracking and eventual head rice recovery

• Varieties differ in their grain cracking and those with low level of cracking such as AG24 is recommended for cultivation (after confirming this results in the next season) When head rice recovery is also considered, OM1490 is better

• There is a clear trend that a few days early harvesting (before maturity) is better than the late harvesting The farmers’ survey results indicate that they harvest the rice mostly late due to labour shortage during the peak harvesting period The intervention opportunity of early harvesting to reduce grain cracking and increase head rice recovery should be conveyed to the farmers and extension agency This extent of this harvesting time effect is also dependent on the variety

• This information gathered will be very useful for the farmers and will be made available through training This will highlight the importance of rapid harvesting

of the crop Farmers are encouraged to make their crop management in such ways that they can harvest earlier (eg, organize labour for harvesting etc)

• This is expected to impact to the farmers decision to determine the harvesting time In some rice varieties this is expected to reduce the losses substantially, since one of the varieties tested in this investigation had a proportion of cracked rice as high as 24%

2 Effect of harvesting methods on the rice cracking , head rice yield and losses 2.1 Effect of harvesting methods on the rice cracking and head rice yield

Harvesting method used can influence the extent of rice cracking in the field The harvesting can be done by hand or machine As a current practice, harvesting by hand is widely used In relation to harvesting method, the cracking of rice is related more to the time duration necessary to harvest than the methods itself A fast harvesting during wet season and harvesting at correct time during dry season is necessary to avoid rewetting or over-drying of the grain while in the panicle Unfortunately, due to the lack of the labours during the harvesting period farmers are not always able to harvest the crop in time which results in losses

This work gathered the actual data to determine the effect of harvesting methods on kernel cracking of some rice varieties in Summer-Spring season (June/July) in Can Tho and Long An provinces The following harvesting methods were used:

1 Hand (+ mechanical threshing)

2 Reaper (+mechanical threshing)

3 Combined harvester (harvesting and threshing combined)

The data were collected from our own experiments as well as from selected farmers field after their traditional harvests

Comparison of harvesting methods by experimentation on the head rice recovery was undertaken in cooperatives in Can Tho and Long An provinces (Table 7) As additional information, cracking behaviour of the grain due to threshing was also investigated in those two cooperatives In each cooperative, the experiments were undertaken in two fields, where the popular rice variety was grown The following results were obtained (Table 7) for each harvesting method applied

Table 7: Effect of harvesting methods on the head rice yield

Average head rice recovery (%)

Hand and heaped immediately HH 41, 50 Hand and dried in the sun (one

*Only one replication due to rain

**Low value due to rain during harvesting

There was a large variation in cracking losses It might be due to varietal difference and other uncontrollable factors It was raining a lot during the experimental period To achieve an accurate result, a large number of experiments should be undertaken to reduce the variability in field condition This was not feasible due to lack of time and restriction

on the resource Therefore, this result should be taken as indicative only The experiments will be repeated in the dry season (Feb/March) The results have indicated that the head rice yield by reaper is better or as good as harvested by hand The main advantage of using the mechanical harvesting is to shorten the harvesting time in order to avoid the effect of rain or weather change difference on the head rice yield We have previously shown that the late harvesting than at maturity will make the grain more sensitive to cracking Therefore, any delay or longer harvesting time can cause more losses, as is the case when the harvesting by hand is practiced

2.2 Effect of harvesting methods on the threshing losses

The above harvesting methods also affected the losses of grain during subsequent threshing step The threshing losses are the fractions of paddy kernels mixed with the impurities removed by the thresher These losses are shown in Table 8

Table 8: Effect of harvesting methods on the threshing losses

Hand and heaped immediately HH 1.4 Hand and dried in the sun (one

In general, leaving the rice one day in the sun after cutting prior to threshing (treatments

HD and RD) reduced threshing losses by 0.2% This reduction can be explained by lower

moisture content of rice after sun drying The average threshing losses by reaper and hand

were 1.0% and 1.3%, respectively The overall threshing loss was 1.1%

Conclusion and project intervention methods:

• The above information indicates that a quick harvesting by reaper method is

beneficial to improve the head rice recovery, but this needs confirmation

• Since, a rapid harvesting is not possible for small farmers due to their limited

financial capacity; operation of harvesters through farmers cooperative is the best

alternative This project implements this concept by providing mechanical

harvesters to two cooperatives

• The cooperatives equipped with harvesters will be used for the demonstration

purpose Data will be presented to the farmers through training The farmers will

be trained through extension workers It is expected that the dissemination of the

information to the local farmers within the catchments area of the cooperative will

be spontaneous due to the engagement of the cooperatives in the activity

• Head rice recovery varied greatly within a system (eg 45-60% in hand and heaped

immediately in GoGon Cooperative), and identification of the source of the

variation would help increase the head rice recovery

3 Other harvesting factors contributing to the losses

There are other factors which can contribute to the post-harvest losses These possible

factors are:

1 Threshing method- hand or machine

2 Shattering of grain due to harvesting method applied

3.1 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 were collected in two provinces at the same time

when experiments were conducted as described in the previous section 1 The results are

presented in Table 9 These results indicated that the grain cracking is not significantly