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Research Article
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Effect of Land Preparation Methods on Growth, Seed Yields of Jasmine 105 Paddy Rice (Oryza sativa L.) and Growth of Weeds, Grown in Northeast Thailand |
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K. Srisa-ard
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ABSTRACT
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This experiment was carried out on a grower`s paddy field, Ban Som Hoeng Village, Kantarawichai, Mahasarakham Province, Northeast Thailand with the use of Roi-Et soil series (Oxic Paleustults) in the rainy season of the 2006 (May to November) to investigate effect of land preparation methods on rice plant heights, amounts of weeds and seed yields of Jasmine 105 aromatic paddy rice (Oryza sativa L.). The experiment was laid in a Randomized Complete Block Design (RCBD) with four replications. The results showed that plant height due to treatments was significantly highest for T3 but T3 was similar to T2, whilst T1 (control) was the least. Mean values of dry weight of narrow leaf type of weeds, in most cases, were significantly lowest with T3 followed by T2 and T3, particularly at the final two sampling periods. Broad leaf type of weeds was significantly highest with T2 throughout the experimental period, whilst T1 and T3, in most cases, were similar. Unfilled seeds were significantly highest with T3 but similar to T1 but T2 was the lowest, whilst filled seeds were significantly highest with T3, both T1 and T2 gave a similar weight. Numbers of panicles m-2 were significantly highest with T3 but T3 was similar to T2, whilst T1 was the least. Seed size or 1000-seed weight was significantly highest with T3, whilst T2 and T1 were similar. Seed yield was highest and highly significant with T3 (1,136.25 kg ha-1) but T3 was similar to T2 (1,083.31 kg ha-1), whilst T1 was the lowest (487.50 kg ha-1). Land preparation method of T3 treatment may be recommended as the first choice, whilst T2 may be used as an alternative choice.
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INTRODUCTION
Rice (Oryza sativa L.) is an important crop being
cultivated for man daily diets in many countries around the world, particularly
Asian countries where rice grains have been used for daily diets for many
centuries. It is a cash crop for growers in Thailand where a considerable
amount of rice yield has been harvested annually, particularly during
the middle of the cold season (November-January) apart from dry season
harvests of the second crop in April or May. It is generally known to
the Thai people that there are more or less three methods of cultivation
being used depending on level of land elevation and labour inputs, i.e.,
(1) upland rice culture, (2) lowland transplanting of rice seedlings,
(3) broadcasting or drilling of rice seeds. The latter method is applicable
to both low and upland paddies where the growers must choose depending
on their investments. The practices in growing rice have been orientated
from generation to generation, i.e., the Thai growers attained their experiences
on different conventional practices from their ancestors such as those
growers who live in the Central Plane region grow rice in their prepared
paddy fields mostly with the use of broadcasting method of rice seeds
(method 3) where their paddy fields were ploughed once or twice followed
by harrowing once whereas growers in northeastern region obviously ploughed
their paddy fields twice within a few weeks followed by harrowing once
and then transplant rice seedlings into rows by hand (method 2), which
could be carried out when rice seedlings reached an age of 25-30 days
after emergence (Anonymous, 2006). However, within this decade such conventional
practice has been, more or less, changed due to lack of labours when a
large number of factories employed young efficient workers into their
factories, thus broadcasting of rice seeds to paddy fields seems to replace
the conventional method.
It is well justified that villagers in all regions of
Thailand annually grow rice mostly for their own consumption apart from
an enormous amount sold out annually mostly for overseas markets, e.g.,
the exportation of rice production during the 2007 reached a figure of
982.77 millions US Dollars (http://www.dft.moc.go.th).
It should be stated that paddy land area of each region of the country
has its different elevations above sea level, e.g., the paddy fields in
the Central Plane area of Thailand has a lower elevation above sea level
than those of northeastern region where most paddy fields in northeastern
region located approximately 200 m above sea level (Suksri, 1999). Furthermore,
the high elevated paddy soils in northeastern region mostly contain a
large amount of sandy soil particles, thus growers face problems in many
respects such as poor soil fertility, i.e., most of the soils possess
low percentages of field capacity, high degree of soil acidity, low percentages
of soil organic matter, poor water retention and many others. Growers
in Northeast Thailand normally separated their paddy fields into blocks
of both different sizes and elevations with the use of ridges where the
ridges of each block prevent the flow out of rainwater to the lower elevated
blocks when each block could always fill up with rainwater in the rainy
season (May-October). Under conditions of erratic rainfall pattern, the
higher elevated paddy blocks could not retain adequate amount of water
then transplanting of rice seedlings may not be possible. Thus broadcasting
or drilling of rice seeds could possibly be the most appropriate methods
to be used in growing rice plants within that season. A number of workers
attempted to find some suitable land preparation methods in growing rice
crop, e.g., Srisa-ard (1982) carried out rice experiment under rain-fed
conditions with the use of different land preparation methods. He reported
that a high frequency in ploughing and harrowing had no significant effect
on rice seed yield but an increase in weeding frequency significantly
increased seed yield. Romyen et al. (1986) showed that ploughing
of paddy field once and left out for a few weeks and then carried out
ploughing again once followed by broadcasting of rice seeds by hand and
harrowing once gave significantly higher seed yields than other methods
of land preparation. They attained seed yield of 2,918.75 kg ha-1.
Furthermore, they stated that ploughing once gave significantly lower
amount of weeds than a high frequency in ploughing. Singh et al. (2001)
carried out rice experiment in comparing seed yields between tillage and
none tillage and between broadcasting of rice seeds and transplanting
of seedlings, he reported that transplanting of rice seedlings gave significantly
higher seed yield than broadcasting. Tillage gave significantly higher
seed yield than none tillage. With the work on weed management of direct-seeded
rice in Malaysia, Vietnam and Thailand, Azmi et al. (2004) reported
that no single control measurement could effectively control weeds in
weedy rice growing. An integrated approach involving cultural, physical
and chemical interventions is expected to be the most effective method
in managing the weeds of weedy rice problem. They further stated that
rice seed yield losses as affected by weeds could be enormous (weedy rice
of 35% infestation could reduce rice seed yield up to 60%). Another work
on rice cultivation reported by McDonald et al. (2006) showed that
the transplanting of rice seedlings gave the highest seed yield ha-1
than other sowing methods. However, 1000-seed weights were similar in
all treated plants.
The present work aims to prove current villagers` practices
whether their accepted method in preparing paddy land areas (method 3)
could be comparable to other two methods (methods 1 and 2) in terms of
growth, seed yield of Jasmine 105 rice and amounts of weed dry weights
in each land preparation method.
MATERIALS AND METHODS
In order to justify the method normally used by growers
in sowing rice seeds of the northeastern region of Thailand, an experiment
was carried out on a villager`s paddy field, Ban Som Hoeng village, Kantarawichai
District, Mahasarakham province, Northeast Thailand in the rainy season
of the 2006 (10th May to 20th November) to investigate effects of land
preparation methods on plant heights and seed yields of Jasmine 105 aromatic
paddy rice (Oryza sativa L.) and also the amounts of weed dry weights
in each treatment. The elevation of the paddy field being used was similar
to upland rice area where ridges were established to prevent the runaway
of rainwater from rice plants, i.e., with normal conditions in the rainy
season, there shall always be some certain amount of rainwater available
on the paddy field throughout the season. Roi-Et soil series (Oxic Paleustults)
of the paddy field was used where the paddy field has been added with
a minimum amount of chemical fertilisers annually, i.e., only with an
approximate amount of 62.50 kg ha-1 of a complete chemical
fertilizer 16-20-0 (N, P2O5, K2 O) was
applied to the paddy field annually. This amount of chemical fertiliser
was applied again for this experiment at the beginning of the experimental
period. The experimental design used was a Randomised Complete Block Design
(RCBD). The paddy field preparation methods used in the experiment were:
ploughing once and left out for a few weeks and then rice seeds were evenly
broadcasted by hand followed by ploughing again once with the use of a
rotavator blades that fixed to a small Kubota tractor unit (T1).
Ploughing once and left out for a few weeks followed by a broadcasting
of rice seeds by hand and then ploughing again once (T2). Ploughing
once and left out for a few weeks followed by a broadcasting of rice seeds
by hand and then ploughing and raking together at the same time once (T3).
A raking tool made from steal of several pieces was used [each piece of
steal stick has a length of approximately 20 cm and all of them fixed
in row (approximately 10 cm apart) to a solid steal with a length of approximately
1.5 m]. The steal pieces could collect weeds when the tractor is at work
and then growers could pull out weeds from time to time during the raking
process. This tool has been designed and made by growers and it is normally
attached or fixed to a small tractor unit. Land preparation of T3
has been widely accepted by growers in Northeast Thailand. A small Kubota
tractor unit was used for both ploughing and rotavated ploughing of the
paddy land area. The plot size used was a 3x6 m with a 2 m walking path
between the plots, each treatment has 4 replications and each replication
was duplicated 5 times for 5 sampling periods of rice plant heights and
weeds, i.e., at days 15, 30, 45, 60 and at the final harvest for seed
yields at day 156 after emergence. Seeds of Jasmine 105 aromatic rice
at a rate of 60 kg ha-1 were evenly broadcasted by hand to
all plots accordingly. Weed dry weights (hot air oven dried at 80°C
for 4 days) of both broad and narrow leaf types were separated into their
categories where appropriate. Seed yield components were determined, i.e.,
(1) number of panicles m-2, (2) number of seeds panicle-1,
(3) number of filled seeds panicle-1, (4) number of unfilled
seeds panicle-1, (5) 1,000-seed weight and (6) finally seed
yield ha-1 was also recorded. Seeds of all treatments were
dried under the sun for 4 days and then weighed out for seed yield determinations.
The obtained data were statistically analysed using an MSTAT-C Computer
Programme (Nissen, 1989).
RESULTS
Rice plant height, dry weights of broad and narrow leaf types of weeds:
At day 15 after emergence, rice plant heights were not significantly
different from each other with plant heights ranged from 15.13 to 15.49
cm for T1 and T3, respectively (Table
1). Similarly, the differences due to treatments were not found with
all sampling periods except at day 156 where this final harvest for rice
seed yields was carried out. At day 156 after emergence, the results showed
that mean values of rice plant height of the rotary blade ploughing treatment
(T1, control) gave significantly lower plant height than T2
and T3. T3 was the highest with mean values of 89.68,
98.96 and 100.78 cm for T1, T2 and T3,
respectively.
For narrow leaf type of weeds, the results showed that at day 15 after
emergence, weed dry weight m-2 was highest with T2
followed by T1 and T3 with mean values of 165.16,
60.02 and 8.16 g, respectively (Table 2). The differences
were large and highly significant. At day 30 after emergence, weed dry
weight of T2 was highest, whilst both T1 and T3
were similar with mean values of 223.83, 47.02 and 21.57 g for T2,
T1 and T3, respectively. The differences were large
and highly significant. At day 45 after emergence, weed dry weights of
T1 and T2 were
Table 1: |
Mean values of
plant heights (cm) of Jasmine 105 aromatic rice as affected by
paddy land preparation treatments, grown on a paddy field, Roi-Et
soil series (Oxic Paleustults) at Mahasarakham Province, Northeast
Thailand |
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Letter(s) in the
column at day 156 after emergence indicate Least Significant Differences
(LSD) at probability (p) ** = 0.05, NS = Non Significant |
Table 2: |
Mean
dry weights (g2 m-1) of narrow leaf type
of weeds in plots of Jasmine 105 aromatic rice as affected by
paddy land preparation treatments, grown on a paddy field, Roi-Et
soil series (Oxic Paleustults) at Mahasarakham Province, Northeast
Thailand |
 |
Letter(s) in each
column and row indicate Least Significant Differences (LSD) at
probability (p) ** = 0.01 |
Table 3: |
Mean dry weights
(g2 m-1) of broad leaf type of weeds in
plots of Jasmine 105 aromatic rice as affected by paddy land preparation
treatments, grown on a paddy field, Roi-Et soil series (Oxic Paleustults)
at Mahasarakham Province, Northeast Thailand |
 |
Letter(s) in each
column and row indicate Least Significant Differences (LSD) at
probability (p) ** = 0.01 |
similar but T3 became least with mean values
of 116.48, 112.73 and 24.29 g, respectively. The differences were large
and highly significant. At day 60 after emergence, weed dry weight was
highest with T1 followed by T2 and T3
with mean values of 309.46, 189.29 and 106.16 g, respectively. The differences
were large and highly significant. At the final harvest for rice seed
yield (day 156), the results showed that amounts of weeds were highest
for T1 followed by T2 and T3 with mean
values of 420.47, 15.76 and 7.62 g for T1, T2 and
T3, respectively. The differences were large and highly significant.
For broad leaf type of weeds, the results showed that at day 15, the
amounts of weed dry weights of all treatments were relatively small with
mean values ranged from 0.85 to 5.19 g for T3 and T2,
respectively. The differences were large and highly significant (Table
3). At
Table 4: |
Mean values of
yield components of filled and unfilled seeds, number of panicles
m-2, 1000-seed weights and seed yields ha-1
of Jasmine 105 aromatic rice as affected by paddy field preparation
treatments, grown on paddy field, Roi-Et soil series (Oxic Paleustults)
at Mahasarakham Province, Northeast Thailand |
 |
Letter(s) in each column and row indicate
Least Significant Differences (LSD) at probability (p) * = 0.05,
** = 0.01 |
day 30 after emergence, weed dry weight was highest with
T2 followed by T3 and least with T1 with
mean values of 8.06, 3.59 and 1.25 g for T2, T3
and T1, respectively. The differences were large and highly
significant. At day 45, T2 gave the highest followed by T3
and T1 was the least with mean values of 19.90, 4.60 and 1.51
g, respectively. The differences were large and highly significant. At
day 60, again weed dry weight of T2 was highest followed by
T1 and T3 where both T1 and T3
were similar with mean values ranged from 1.98 to 22.52 g for T1
and T2, respectively. The differences were large and highly
significant. At the final harvest for rice yield (at day 156 after emergence),
the results showed that weed dry weights of all treatments became smaller
than any other previous sampling periods, i.e., T2 gave the
highest followed by T1 and T3 where T1
and T3 were similar with mean values ranged from 0.09 to 1.60
g for T3 and T2, respectively.
Yield components, number of panicles ha-1, 1000-seed weight
and seed yields: For rice seed yield components, the results showed
that number of unfilled seeds panicle-1 was highest with T3
followed by T1 and T2 with mean values of 6.95,
5.85 and 2.43 seeds, respectively. The differences were large and highly
significant (Table 4). With filled seeds panicle-1,
the results revealed that filled seeds were highest with T3
followed by T1 and T2 with mean values of 81.60,
46.60 and 41.70 seeds, respectively. However, T2 was not significantly
different from T1. With number of panicles m-2,
the results showed that T2 and T3 were similar but
T1 was the least with mean values of 100, 113 and 38 panicles,
respectively. The differences were large and highly significant. For 1000-seed
weight, the results showed that T3 was the highest followed
by T2 and T1 with mean values of 26.26, 25.48 and
25.14 g, respectively. However, T1 and T2 were not
significantly different from each other. For seed yields, seed yield ha-1
was highest with T2 followed by T3 and the lowest
was with T1 with mean values of 1136.25, 1083.31 and 487.50
kg ha-1, respectively. The differences were large and highly
significant.
DISCUSSION
In growing rice crop under rain-fed conditions, growers
of lowland paddy in Northeast Thailand normally cultivate their rice plants
in the rainy season, i.e., starting from May to November. Within the months
of the rainy season, monsoon normally comes and then cool weather with
short day-length follows in October. Most growers in Northeast Thailand
normally plough their paddy fields once and left them out for a few weeks
to allow all buried grasses or plant materials after ploughing to decompose
and then they plough the paddy fields again once follow by broadcasting
of rice seeds and a raking follows. They usually broadcast rice seeds
to their paddy fields in May or June to obtain a dense amount of young
seedlings and when the seedlings reach an age of 25-30 days after emergence
then growers pull out their seedlings for transplanting into their paddy
fields. The paddy field being used for transplanting of rice seedlings
must be ploughed again followed by raking once. The method in transplanting
rice seedlings has been practiced for many decades and it is known as
a conventional practice in rice culture in Northeast Thailand. This method
in rice culture normally provides a considerable amount of seed yields
at the final harvest if a severe drought condition was not occurred during
the growing period (Tongkamdee, 2006). The high seed yield attained with
transplanting of rice seedlings was also found with the work of Singh
et al. (2001) where he compared seed yields among other treatments
used.
In Thailand, now a days the practice in transplanting
rice seedlings has been declined due to lack of labour inputs as a result
of industrialization of many products such as clothing, food processing,
electronic components and many others where a number of youngsters stay
away from their paddy fields but migrated to many factories of industrial
zone instead. This phenomenon has caused a huge problem for villagers
who grow rice although some sorts of mechanization have been employed
during the past decades but it is rather expensive to invest and many
growers could not afford it but hiring a tractor unit to work on their
paddy fields where the hiring cost for paddy preparation could be relatively
high with a small margin of profit at the final harvest. Thus large numbers
of growers have shifted themselves from the conventional method of transplanting
rice seedlings to broadcasting of rice seeds to their paddy fields instead.
In practicing this way, nowadays growers realized that their annual harvests
of rice seed yields became relatively small compared with that of the
transplanting method due to many reasons such as (1) broadcasting method
creates a tremendous amount of weeds, particularly when erratic rainfall
occurred, i.e., a few centimeters of water above ground level was not
available for rice plants since no rainwater filled up the paddy fields.
This condition normally favours the germination of weed seeds and it is
generally found with many higher elevated paddy areas in Northeast Thailand,
(2) poor growth of rice plants with, more or less, no tillers could be
produced due to small spaces available for rice plants to develop tillers,
(3) it may be possible that a large amount of roots of rice plants could
not be developed due to perhaps a high competition for nutrients among
rice plants and weeds and also the competition for radiant energy or even
CO2 uptake.
It was found with the results of this work that there
were no significant differences on plant heights due to the three methods
of paddy land preparation, i.e., commencing from the first up to the fourth
sampling periods except at the end of the experimental period (at day
156 after sowing) when the final sampling of all treatments were harvested,
i.e., T3 gave a mean value of plant height significantly higher
than control (T1) but similar to T2. The results
suggested that the use of rotavator blades for digging or ploughing the
paddy land after the broadcasting of rice seeds of T1 may not
be a suitable method in growing rice due to perhaps some amounts of seeds
did not bury into the soil or some could have been buried at a considerable
depth thus poor germination could have been occurred and perhaps birds
and insects could have taken away some amounts of the seeds those left
out on the soil surface. It was found that a moderate amount of annual
rainfalls was attained during the experimental period. Therefore, the
method used for T1 may not be an appropriate method for growers
to practice. The method used with T2 could probably be better
although T2 gave seed yield not significantly different from
T3 but highly significant over T1. There should
be some advantages derive from T2 under a condition that if
it is so happened that in a year when erratic rainfall pattern occurs
when rainwater may not plentiful then high percentages of germination
of seeds of T2 could have been achieved due to a moderate amount
of soil moisture content in soil aided germination of seeds, particularly
those buried in soil at a considerable depth. However, a reverse condition
may be resulted if rainwater could have been plentiful in that year then
a condition on water-logging could have been occurred, hence the germination
of seeds may not be possible thus the practice of T2 may not
be of advantage (Srisa-ard, 1982).
It was found that narrow leaf type of weeds of T3,
in most sampling periods, were relatively smaller than the rest. However,
with broad leaf type of weeds of T3, in most cases, was significantly
higher than control (T1), particularly at days 30 and 45 after
emergence but later both became similar. The results indicated that the
use of rotavator blades in rotavating or ploughing the paddy soil of T1
may have caused some relative effects on weed seeds of broad leaf type
perhaps by buried seeds into the soil at a considerable depth where the
seeds were not able to germinate hence the amount of collected weeds were
relatively smaller for T1 than T3. Another reason
for this could have been due to previous availability of weed plants in
the chosen plots, which were perhaps lesser for T1 than T3.
A better result on weed problems among the treatments with respect to
seed yields was found with T3 where growers recognised the
preparation of land of this method as a replacement of the conventional
method. It seems more likely that growers must have had experiences or
tested this method for several seasons long before they decided to choose
this method as the most appropriate method for their land preparation.
When it comes to yield components, the results showed
that unfilled seeds were similar for T1 and T3 but
with filled seeds, it was found that T3 gave the highest where
T1 and T2 became similar. This could possibly be
attributable to perhaps the small amount of weeds of both types (narrow
and board leaves) and the rapid growth of both roots and leaves of the
rice plants of T3 as a result of the lesser amounts of weeds
than the other two treatments favoured the rapid filling up of seeds.
Romyen et al. (1986) stated that broadcasting of rice seeds created
weed problems enormously and rice seed yields decreased significantly.
The lesser amounts of weeds with T3 than the rest could have
been due to the raking practices when most grown weeds were taken away
by hand at the time of raking. Tindall et al. (2005) reported that
high amount of weeds significantly affected rice seed weight than the
effect due to the damages caused by rice stink bug where this type of
insects affected quality of rice grains rather than seed yield. A large
amount of weeds in the paddy field area could always affect growth and
yields of rice plants as reported by Srisa-ard (1982) where he attained
only a maximum seed yield of 967 kg ha-1 with direct seeding.
Similarly, Watanabe et al. (1997) and Azmi and Abdullah (1998)
carried out experiments on paddy rice they stated that weeds of many kinds
severely and significantly reduced rice yields at harvests.
Some considerable amount of paddy rice seed yield (2077.50
kg ha-1) derived from direct seeding was attained with the
experiment reported by Karnjana (2001) where he added cattle manure to
the paddy field at a rate of 6,250 kg ha-1 together with a
complete chemical fertiliser at 30-30-15 (N-P2O5-K2O)
kg ha-1. He stated that most paddy field requires some large
amounts of animal manure, particularly cattle manure. The highest seed
yield (kg ha-1) found with this work was relatively lesser
than the experiment reported by Tongkamdee (2006) where he obtained an
average seed yield of rice in northeastern region of Thailand up to 1,875.00
kg ha-1 with the use of transplanting of rice seedlings. With
the present work, the highest seed yield was attained with T3
(1,136.25 kg ha-1). However, this amount of seed yields may
be recognised as a high level of seed yield. This could possibly be attributable
to the low amount of chemical fertiliser applied to the paddy soil (62.50
kg ha-1 N, P2O5, K2O) and
above all this soil series is one of many poor soil series found in Thailand.
Thus poor soil fertility apart from the effect due to the high amount
of weeds tremendously affected rice seed yield. The seed yield of T3
may be improved largely if some amounts of chemical fertiliser had been
added again to the rice plants, at least of the same amount as applied
with initial application, particularly during the vegetative stage or
perhaps the application should be done at approximately a few weeks prior
to booting stage. Thus land preparation method of T3 could
be most appropriate if soil fertility could be relatively high. The method
used with T2 could be another choice for growers to choose
when erratic rainfall occurs but it could be rather risky and it is difficult
to forecast the conditions of the weather. For the results of this study,
it may be possible to state that the practice of T3 could be
somewhat of a retrospective explanation of what and why growers practice
this method rather than other methods. It may be of important value to
find some further means and ways to eliminate weeds in paddy fields before
broadcasting of rice seeds such as the use of ploughing twice at 3 week
intervals and the sowing of dense legume crops right after each harvest
of rice yield. The practice in crop rotation or the rotating crop patterns
may be off help, particularly the use of legume crops of a high leaf density
to cover the ground areas such as soybean, cowpea, mung bean, African
sesbania and others where shading of leaves of legume crops could avoid
the germination of weed seeds and at the same time the plant materials
of these legume crops could help in improving soil fertility, particularly
soil nitrogen. The growth of legume crops could largely increase soil
nitrogen has been reported by Russell (1988), Garrity and Flinn (1988),
Lizhi (1988), Miller and Donahue (1990), Rekhi and Bajwa (1993), Suksri
(1999) and Srisa-ard (2007).
From this investigation, one may find that there is an
urgent need to establish an intensive long-term fertility programme for
paddy land areas perhaps not only with the land area being used for this
work but with all paddy rice fields in Northeast Thailand so that average
annual rice seed yields ha-1 could be largely improved and
seed yields could be comparable to other countries.
To sum up, the results showed that rice plant height
was significantly highest with T3 but T3 was similar
to T2, whilst T1 was the lowest. Dry weights of
narrow type of weeds were significantly highest with T1, whilst
T2 was similar to T3. Dry weights of broad leaf
type of weeds were highest with T2, whilst T1 and
T3 were similar. Amount of unfilled seeds panicle-1
was highest with T3 but T3 gave highest amounts
of filled seeds panicle-1 and also T3 gave the highest
number of panicles m-2. 1000-seed weight was significantly
highest with T3, whilst seed yield ha-1 was highest
with T3 but T3 was similar to T2. T3
treatment was considered to be the best land preparation method.
ACKNOWLEDGMENTS
The author wishes to thank Mr. Tongdee Somkid for his
kind assistance during this work was carried out. Thanks are also due
to staff members and personnel of the Department of Agricultural Technology,
Faculty of Technology, Mahasarakham University. Prof. Amnuaysilpa Suksri
for his kind assistance in preparing the manuscript.
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