Optimum Rice Density and Herbicide Application in Direct Seeding in Ahwaz Region, Iran
In order to investigate of rice and barnyard-grass in
different levels of herbicide and crop density, an experiment was conducted
in split plot design with four replicate, in research farm of Ramin Agriculture
and Natural Resources University in 2006. Four herbicide doses (0, 3,
5 and 7 L ha-1) was arranged in main plots and three seeding
rates (100, 120 and 140 kg seed ha-1) in subplots. Interaction
of herbicide and crop density on dry matter and yield of rice and barnyard-grass
was significant. Therefore, response of variance trends of these traits
to herbicide in different densities was different. While no herbicide
was be used, rice yield in density 120 was higher than other densities,
that showed that optimum crop density could increased crop competition
ability and decreased herbicide use. In other hand, it be observed that
highest and lowest yield of crop and weed, respectively, was be related
to 5 L herbicide ha-1. In this case, there was little difference
between different densities. With more herbicide use, probably due to
toxicity effect, crop yield decreased. However, in this herbicide dose,
density 120 showed lesser changes in crop yield. In density 120, crop
and weed yield relationship have lesser slope in comparison with other
densities. Ultimately, it seems that optimum crop density can lessen crop
sensitivity to other environmental and agronomic factors including weed
competition and herbicide use.
Among common weeds, barnyard-grass (Echinocloa crus-galli) has the most
abundance and economic importance in rice fields. With regarding to worker deficit
and increasing fees, chemical method is most simple and cheap method to control
weeds. However, most researches are conducting to reduce herbicide use through
increase crop competition ability (Kim et al., 2006).
Many efforts have been made to investigate the effects of reduced doses of herbicide
on crop-weed competition in cereal crops, such as spring barley (Christensen,
1994), winter wheat (Brain et al., 1999) and
spring wheat (Salsonen, 1992). Studies on reduced doses
of herbicide have also been conjunction with various cultural practices, such
as seeding rate and crop density (Shibayama, 2001). Crop
density has a key role in weed management. Optimum crop density result in rapid
shading on soil surface and prevent weed growth (Radosevich
et al., 1997). However, Kevin et al. (2001)
indicated that different rice densities in direct seeding have no significant
effect on barnyard-grass growth. Transplanted rice seedlings, especially larger
ones, are much more competitive with weeds than direct-seeded plants (Shibayama,
Regulations for protecting environment from pollution from agriculture have
encouraged farmers to use less inorganic input including herbicides. Kevin
et al. (2001) showed that use 4.5 L molinit ha-1 in flooding
direct rice seeding, decreased Dry Matter (DM) and tillering of barnyard-grass,
significantly. In other hand, Lesnik (2003) indicated
that herbicide use efficiency increased by optimum crop density in maize. The
objective of this study was evaluation interaction of herbicide and seeding
density of rice to reduce herbicide use through optimum density.
MATERIALS AND METHODS
An experiment was carried out in 2006 at Ramin Agriculture and Natural resources
University, Ahwaz, Iran. The experimental design was split plot in RCB with
four replications. Four herbicide doses (0, 3, 5 and 7 L molinit ha-1)
were arranged in main plots and three rice seeding rates (100, 120 and 140 kg
seed ha-1) were arranged in sub plots. Cultivar LD183 (late maturing
cultivar) was be used in this experiment. In order to have monotony and to have
40 barnyard-grass shrubs per squared meter, 4.8 g seed of this weed was spread
in plots. Rice seeds were spread monotony and directly in plots. Statistical
Analysis Systems (SAS) and excel software were be used to analysis data of experiment.
Because of significant interaction between factors, main effect of each factor
was not be evaluated. Finally, regression analysis was carried out for data
(Gomez and Gomez, 1984).
RESULTS AND DISCUSSION
DM and GY of Crop and Weed
Results showed that seeding density and herbicide had significant
effects on rice and barnyard-grass dry matter, DM and grain yield, GY
With increase herbicide use up to 5 L ha-1, DM of rice increased
significantly (Fig. 1). Herbicide use more than 5 L
ha-1 up to 7 L ha-1, result in decrease rice DM
in 100 and 140 kg seed ha-1, but had no effect on DM in density
120 kg seed ha-1. Also, while no herbicide was be used, rice
DM in density 120 was higher than two other densities. Generally, herbicide
effect on DM was lower in density 120 in comparison with other densities.
|| Analysis of variance of GY and DM in rice and barnyard grass
|**Significant μm 1 (%) probability
|| Effect of herbicide and seeding rate on DM of rice
|| Effect of herbicide and seeding rate on DM barntard-grass
|| Effect of herbicide and seeding rate on GY of rice
In other hand, DM of barnyard-grass while no herbicide applied, in density
120 was lower than other densities, significantly (Fig. 2).
With increase herbicide, DM of barnyard-grass decreased earlier in densities
100 and 140, in comparison with density 120 kg seed ha-1. However,
in all herbicide doses, DM of barnyard-grass was lowest in density 120 kg seed
ha-1. It seems that in optimum crop density, lesser herbicide will
be required (Lesnik, 2003).
The GY of rice in density 120, while no herbicide applied, was higher than
two other densities (Fig. 3). With increase herbicide up to
5 L ha-1, GY increased in all densities. However, application herbicide
up to 7 L ha-1 could not increase competition ability and GY of rice.
It is probably due to rice shrubs toxicity. Highest GY of rice was gained with
5 L herbicide ha-1 and 120 kg seed ha-1. The GY of barnyard-grass
with no herbicide in density 120 was lower than other densities, significantly
(Fig. 4). It showed that weeds will be controlled better in
optimum crop density. With herbicide application, GY of barnyard-grass decreased
significantly, in densities 100 and 140 seed ha-1, that show higher
demand to herbicide in these densities.
|| Effect of herbicide and seeding rate on GY of barnyard-grass
|| Relationship between GY of Rice and barnyard-grass in different
Crop and Weed Yield Relationship
Regression analysis showed that with increase GY of barnyard-grass, GY of
rice decrease linearly (Fig. 5). It was expected, but this trend
in densities 100 and 140 kg seed ha-1 was severe in comparison with
density 120 kg seed ha-1.
With increase herbicide dose, weed could be controlled, significantly.
But exceeded dose of herbicide, can be also toxic for crop. In addition,
it is possible that a reduced herbicide dose will be adequate for weed
control while seeding rate is optimum.
It seems that in density 120, weeds could be more controlled than other
densities and a better nutritive space will be provided for rice. These
conditions can be helpful for crop in competition in barnyard-grass.
Ultimately, it seems that optimum seeding rate as a good crop density
can decrease crop sensitivity to weed competition and herbicide use.
These finding showed that integrated weed control procedures could be
helpful in direct seeding of rice to maximizing rice yield with reduced
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