Introduction
Rice (Oryza sativa L.) is an important cereal crop of the world (FAO 2019).
It fulfils food needs of about 90% population of Asia and more than half of the
world’s population (Fukagawa and Ziska 2019). In Pakistan, it is very important staple food and
main exportable cash crop which contributes in agriculture and gross domestic
product (GDP) by about 3.0 and 0.6%, respectively (GOP
2018–19). Its production is very
important for the livelihood of about billions of people. Besides the
availability of high production varieties, pesticides, fertilizers and other
agronomical resources, its production and area has not been increased.
Presently at global scale, its production in irrigated areas is mostly affected
by the water scarcity, poor management of inputs and resources and losses from
weeds, pests and diseases across the world (Jabran et al. 2017; Rao et al.
2017). Besides some natural factors of climate change, management practices
including untimely sowing, inappropriate irrigation management and inadequate
weed control may also be a hindrance in getting higher rice yield. For the
sustainable agriculture, a new approach to rice cultivation the system of rice
intensification (SRI) has emerged as an alternative rice production method
being eco-friendly, sustainable and productive as compared to the conventional
rice production techniques (Glover 2011). It is a system rather than a
technology and is based upon the ideas of getting more outputs from fewer
inputs (Uphoff 2003). The SRI requires fewer inputs like seeds, fertilizers,
pesticides, water and gives high yield (Styger et al. 2011). It has been indorsed as a management approach of crop
in integration with resources for the more rice cultivation (Tsujimotoa et
al. 2009). This system also plays
an important role as a mechanical weed management approach against major weeds
in rice field (Styger et al. 2011).
It is also stated that the reduced plant density of rice grown through SRI is
compensated by increased yield per plant through high numbers of fertile
tillers and panicles (Menete et al.
2008). This system also discourages the use of chemicals; however, are applied
if necessary (Thakur et al. 2010a).
The SRI leads to the better agronomic and phenotype performances for rice
genotypes at variable range (Lin et al.
2005, 2006). It provides less competition, more space, and the interaction by
allelochemicals to the growing roots and this system is eventually also leading
to more production of dry matter of every hill in the rice crop (San-oh et al. 2004). The system of rice
intensification ensures the source of sunlight and air to the single plant in
wide spacing of rice plants and settlement of individual seedling hill-1
(Satyanarayana et al. 2007). Single
plant spacing in transplanted rice seedling plays a vital role in a variety of
physiological and agronomical parameters, resulted to improve, or reduce the
production of rice crop (Mishra and Salokhe 2010). It is well known that weeds
are the major restrictions to high yield and the
effective weed management is the major problem for the farmers (Singh et al. 2003). Under all conditions, no
one is the best weed controlling method (Riaz et al. 2006). The density of weed, competition period, type, growth
stage, crop sowing time and method are the major reasons of the losses in crop
yield due to un-controlled weed emergence (Ashiq et al. 2003; Mansoor et al.
2004). About 80% losses in grain yield occur due to un-checked weed growth (Babu et al. 1992). The competition between rice crop and weeds start at their
specific growth stage and if it is kept uncontrolled, then up to 50–60% yield
losses may occur under puddled transplanting conditions (Dass et al. 2017). Under the traditional
system of rice transplanting, the initial 40 days after
transplanting were considered critical for crop-weed competition in rice (Thapa
and Jha 2002). All the yield related traits are
affected by weed competition duration (Uremis et al. 2009) and there is no effect on yield after critical weed
competition period (Johnson et al.
2004).
In
contrast to SRI, a modified system of rice intensification (MSRI) has been
developed using higher transplant density that was proved to be more successful
as it gained higher rice yields, sustained soil fertility and farmers’ income (Das et al. 2018). In MSRI, it
was supposed that narrow plant spacing could
enhance the crop yield by the increased number of tillers per unit area that
allows lesser weeds to grow among crop plants. Dass et al. (2017) documented that narrower
plant spacing in puddled transplanted rice resulted in higher productivity with
minimum weed infestations. However, by modifying the
planting geometry of rice, there will definitely be a change in critical
weed-crop competition period. Therefore, there was dire need to find out the
most suitable plant spacing for Super Basmati rice cultivar and to explore the
critical weed-crop competition period under
variable plant spacing so that farmers and the researchers will know the best
time to manage the weeds in rice fields economically before or after which they
would be losing their money and time. Keeping in view the potential benefits of
SRI observed by different researchers in various rice growing countries, it was
the need of time to validate this technology under agro-ecological conditions
of Punjab, Pakistan. Therefore, this two-year field study was planned to know
the effect of plant spacing and the critical
period of weed competition in rice crop sown through SRI and the goal of this
study was to provide an appropriate package to the rice growers for the best
resources utilization at the most suitable time and management of the
problematic weeds in SRI.
Materials and Methods
Site description
This field study
was conducted in 2010 and 2011 at the Agronomic Research Area, University of
Agriculture, Faisalabad, Pakistan and the experimental site location was 30.35–31.47°N
latitude, 72.08–73°E longitude and at 150 m altitude. The principles and
practices of the system of rice intensification were followed during soil,
water and crop management (Stoop et al. 2002). Soil
of investigation site was loam having organic matter 0.98 and 1.08%, pH 7.6 and
7.7, total nitrogen (N) 0.053 and 0.056%, available phosphorus (P) 12.9 and
13.3 mg kg-1 and available potassium (K) 128 and 132 mg kg-1
of soil during years 2010 and 2011, respectively. Average rainfall of season
was 96.98 mm in 2010 and 74.08 mm in 2011.
Treatments and experimental
details
Rice was
transplanted using different transplant spacing (PS) as 20 cm × 20 cm, 25 cm × 25 cm and 30 cm × 30 cm under various weed
competition periods (CP) viz., 20,
40, 60 and 80 DAT (days after transplanting). A weedy check and weed free
period for whole crop season were kept as controls. The experiment was conducted in the randomized
complete block design (RCBD) with split plot arrangement and there were three
replications for each treatment. The net plot size was 3.0 m × 6.0 m for each
treatment and plant spacing factor was allocated to main plots while weed
competition period to sub-plots.
Crop husbandry
The bed for raising rice nursery was prepared in close proximity of the
study field to be transplanted with these seedlings to avoid seedling shock at
the time of transplanting (Thakur et al. 2010b). Well-rotted farm
yard manure at the rate of 1 kg m-2 was mixed thoroughly with the
soil before seed sowing. The paddy (CV. Super Basmati) seeds were soaked in the
tap water for 10 min in a bucket and sank seeds were used for sowing while the
floated seeds were discarded. The seed rate of 1.25 kg per 25.32 m2
was broadcasted for sowing and covered with rice straw to preserve moisture and
guard of germinated seed from predators. At the time of field preparation for
transplanting, the farm yard manure was mixed thoroughly with soil at the rate
of 5 t ha-1 and rice seedlings of 21 days were transplanted in the
prepared field. Muddy conditions were maintained by the applying water in the
field during transplantation (Thakur et
al. 2010b) and no synthetic fertilizer was applied. Rice seedlings were
transplanted using one seedling per hill and assuring that the root tips were
not inverted upward. For the initial two weeks after transplanting, irrigation
was applied three times per week to maintain 3 cm standing water in the field.
After that, an alternate wetting and drying schedule was followed up to the
start of grain formation and making sure that irrigation was applied only after
drainage of ponded water. From the grain formation to the harvesting, 3 cm
irrigation was applied with the five days’ interval.
Crop harvesting and data recording
Three major weeds such as Echinochloa colona L., Trianthema portulacastrum L. and Cyperus
rotundus L. were dominant
in the rice field. Weed density and weed dry biomass were recorded at 55 and 85
DAT, respectively to observe the weed dynamics. In each experimental unit, a
quadrate having the size of 0.5 m × 0.5 m was placed randomly at two
different points and weeds were counted
for the measurement of weed density and cut from base to measure fresh and dry
weight. Two readings of weed density and dry weight were obtained per plot and
the values were averaged and converted into m-2. For the
measurement of rice root length, the plants were dug-out from the soil and
their roots were washed with tap water and the length of the longest root was
measured by the measuring scale/tape from the stem-root junction to the end of
the root tip and the roots of individual plants
were removed from the above ground part to measure the root mass by the help of
electronic balance. To record the
number of fertile tillers per hill, ten hills from every experimental plot were
randomly selected and counted the number of panicle-bearing tillers and
averaged. The 1000-kernel weight was taken in gram by electronic balance after
taking three normal kernel samples from each treatment of each replication and
taken its average. Normal kernels (lucid, translucent and immaculate)
were counted and their percentage was calculated by dividing with total number
of kernels. Kernels yield was taken after harvesting whole plot by sickle and
threshing manually, and the yield recorded was converted into kg ha-1
of clean rough rice at grain moisture content of 14%.
Statistical analysis
The Fisher’s two-way analysis of variance (ANOVA)
technique was applied for analysis of recorded data, and the LSD (least
significant difference) test was used at 5% probability to compare the
significance among treatment means (Steel et
al. 1997).
Results
Weed growth characteristics
The interaction of different transplant spacing and weed competition
durations or periods significantly affected the weed density and weed dry
biomass of three major weeds i.e., E. colona, T. portulacastrum, and C. rotundus in SRI field (Table 1). The strong relationship between total weed
density and weed competition period was presented in Fig. 1. The data explained
that minimum (17.0 and 21.3 m-2) total weed density was seen when
the combination was PS1 × CP2 (20 cm × 20 cm spacing and
20 DAT weed competition period) during both the years excepting the weed free
combinations with all the spacing, and the value of minimum total weed density
was statistically as par with 20.7 and 24.7 m-2 that was recorded in
the situation of PS2 × CP2 (25 cm × 25 cm spacing and 20
DAT competition period). With the increase in the spacing of rice plants and
the competition period of weed, the total weed density also gradually increased
and reached at maximum values of 96.0 and 103 m-2 during 2010 and
2011, respectively, at 30 cm × 30 cm spacing in competition of weed for full
growth period/weedy check (PS3 × CP1). The individual
density of all the three weeds including E.
colona, T. portulacastrum, and C. rotundus also followed the same
trend during the both years of the study. However, among these weeds, C. rotundus density remained the highest
whereas T. portulacastrum
and E. colona
remained at second and third position, respectively, with respect to their
densities. Similarly, the
lowest total dry biomass (5.5 and 8.4 g m-2) was measured at PS1 × CP2
(20 × 20 cm spacing in 20 DAT competition period) throughout both years and
highest total dry biomass (94.1 and 100.5 g m-2) was calculated at
PS3 × CP1 (plant spacing 30 cm × 30 cm and control/weedy
check) (Table 1). Individual weed dry biomass also followed the similar trend
as shown by total weed dry biomass in response to different plant spacing in
combination with different competition periods. The strong relationship between
total weed dry weight and competition period has been shown during both years
of study (Fig. 2).
Root growth, yield and yield contributing
traits of rice
Table 1: Effect of plant spacing and competition period on weed density and dry
biomass in rice
|
Treatments |
Weed
density (plants m-2) |
Weed dry biomass (g m-2) |
|||||||||||||||
|
Total |
Echinochloa colona |
Trianthema portulacastrum |
Cyperus rotundus |
Total |
Echinochloa colona |
Trianthema portulacastrum |
Cyperus rotundus |
||||||||||
|
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
||
|
PS1 |
CP1 |
81.3c |
86.0c |
6.3a-c |
7.0bc |
18.0bc |
18.7bc |
57.0b |
60.3c |
81.4c |
86.6c |
13.6ab |
14.6b |
20.3c |
21.8c |
47.5c |
50.2c |
|
CP2 |
17.0l |
21.3l |
1.0i |
1.3gh |
1.7l |
2.3j |
14.3k |
17.7j |
5.5m |
8.4n |
0.9j |
1.3g |
1.3k |
2.1j |
3.3j |
5.0k |
|
|
CP3 |
39.3j |
43.7j |
3.0f-h |
4.0ef |
4.7i-k |
5.0hi |
31.7i |
34.7h |
26.3k |
30.6l |
4.1i |
5.3f |
5.4i |
6.6i |
16.7i |
18.7i |
|
|
CP4 |
56.3gh |
62.0gh |
4.0e-g |
5.0de |
9.7h |
11.7ef |
42.7fg |
45.3f |
43.8h |
48.7i |
6.1gh |
7.7e |
10.3g |
11.6g |
27.4f |
29.4g |
|
|
CP5 |
67.3ef |
72.0ef |
5.0c-e |
6.0cd |
14.3ef |
16.0d |
48.0de |
50.0e |
59.6e |
65.0f |
9.7de |
11.4c |
16.0e |
17.3e |
33.9e |
36.3e |
|
|
PS2 |
CP1 |
87.7b |
93.5b |
7.0ab |
8.0ab |
19.0b |
19.8b |
61.7a |
65.7b |
89.1b |
94.0b |
15.3a |
15.3b |
22.9b |
24.0b |
50.9b |
54.7b |
|
CP2 |
20.7kl |
24.7l |
1.3hi |
2.0g |
2.7kl |
3.0ij |
16.7jk |
19.7j |
7.0lm |
10.2n |
1.1j |
1.6g |
2.1jk |
3.2j |
3.8j |
5.5jk |
|
|
CP3 |
46.7i |
51.0i |
4.3d-f |
5.0de |
5.7ij |
6.0gh |
36.7h |
40.0g |
31.1j |
35.6k |
4.9hi |
5.6f |
6.1hi |
7.2i |
20.0h |
22.7h |
|
|
CP4 |
62.3fg |
67.0fg |
5.0c-e |
6.0cd |
10.7gh |
11.3f |
46.7ef |
49.7e |
47.7g |
52.0h |
7.3fg |
8.2e |
11.3fg |
12.4fg |
29.1f |
31.5f |
|
|
CP5 |
72.0de |
78.0d |
6.0bc |
7.0bc |
15.3de |
17.3cd |
50.7cd |
53.7d |
62.9e |
67.6e |
10.7cd |
12.2c |
16.6e |
17.6e |
35.7e |
37.8e |
|
|
PS3 |
CP1 |
96.0a |
103.3a |
8.0a |
8.7a |
22.0a |
24.3a |
66.0a |
70.3a |
94.1a |
100.5a |
15.3a |
16.9a |
24.6a |
26.9a |
53.9a |
56.7a |
|
CP2 |
26.7k |
30.3k |
2.3g-i |
2.7fg |
3.7j-l |
4.0h-j |
20.7j |
23.7i |
9.4 l |
13.0m |
1.6j |
2.3g |
2.9j |
3.6j |
4.9j |
7.1j |
|
|
CP3 |
52.3hi |
57.3h |
5.0c-e |
6.0cd |
6.7i |
7.3g |
40.7gh |
44.0f |
39.1i |
44.2j |
6.6f-h |
7.7e |
7.5h |
8.9h |
25.0g |
27.6g |
|
|
CP4 |
69.0e |
74.3de |
6.0b-d |
7.0bc |
12.7fg |
17.7e |
50.3de |
53.7d |
55.3f |
60.6g |
8.2ef |
9.7d |
12.4f |
13.7f |
34.7e |
37.2e |
|
|
CP5 |
78.0cd |
84.7c |
7.0ab |
8.0ab |
16.7cd |
18.7bc |
54.3bc |
58.0c |
75.1d |
81.2d |
12.6bc |
14.3b |
18.6d |
19.5d |
43.9d |
47.4d |
|
|
LSD(P≤5%) |
6.26 |
5.04 |
1.67 |
1.63 |
2.13 |
2.30 |
4.63 |
3.61 |
3.84 |
2.40 |
2.01 |
1.28 |
1.55 |
1.66 |
2.08 |
1.97 |
|
The
means following the same letters, within a column for each trait, did not
significantly differ at 5% probability level
Plant
spacing (PS1= 20 cm ×20 cm, PS2= 25 cm ×25 cm, PS3=
30 cm × 30 cm); Weed crop competition periods (CP1= weedy
check/control, CP2= 20 DAT (Days after transplanting), CP3=
40 DAT, CP4= 60 DAT, CP5= 80 DAT
The interactive effect of different rice plant spacing and weed
competition durations on the root growth, yield and yield contributing traits
of rice remained significant during both the year of study (Table 2). Data
indicated that the highest root length (30.9 cm and 30.0 cm) and root biomass
(34.5 g and 32.9 g) was achieved by rice plants harvested from plots with
widest plant spacing (30 cm × 30 cm) in weed free conditions (PS3×CP6).
This combination however did not differ significantly from plant spacing of 25
cm × 25 cm in interaction with no weed competition (PS2 × CP6)
regarding root length and root biomass throughout both experimental years. A
significant decline in root length and biomass started to occur by decreasing
rice transplant spacing to 20 cm × 20 cm under the same without weed
conditions. Consequently, the narrowest plant spacing (20 cm × 20 cm) in
combination with weedy check (PS1 × CP1) produced the
lowest rice root length (12.2 and 11.4 cm) and root biomass (10.0 and 9.6 g)
(Table 2).
%201142-1148_files/image002.png)
Fig. 1: Relationship between competition period and total weed density in rice
under system of rice intensification as affected by competition period during
2010 and 2011
Similarly, the highest fertile tillers per hill (55.8
and 53.4), 1000-kernal weight (24.7 and 23.8 g) and normal kernel percentage
(81.37 and 79.13 %) were recorded with 30 cm × 30 cm transplant spacing in no
weed competition (PS3 × CP6)
while the kernel yield was maximum (5.6 and 5.6 t ha-1) in the
interaction of PS2 × CP6 (25 cm × 25 cm transplant
spacing with no weed conditions) during years 2010 and 2011, respectively. However,
the maximum values of fertile tillers hill-1, 1000-kernal weight and
normal kernel percentage were statistically similar to those noted with 25 cm ×
25 cm transplant spacing in interaction with the absence of weed competition
(PS2 × CP6). The count of fertile tillers per hill and
the percentage of normal kernel were proved more sensitive to weed infestation
as these were prone to significant reduction under weed competition in all
plant spacing. While, the lowest count of fertile tillers hill-1,
1000-kernal weight and normal rice kernel percentage were calculated in
combination of any of rice transplant spacing (PS1=20 × 20 cm, PS2=25
× 25 cm, and PS3= 30 × 30 cm) with full season competition (CP1=weedy
check), while the lowest rice kernel yield (1.8 and 1.8 t ha-1) was
achieved in the interaction of 30 cm × 30 cm spacing of rice transplantation
with full season competition (PS3 × CP1) throughout the
both years of experimental study (Table 2).
Discussion
Table 2: Effect of plant spacing and competition period on root length, root
mass, fertile tillers, 1000-kernel weight, kernel yield and normal kernels
|
Treatments |
Root length (cm) |
Fertile tillers hill-1 |
1000-kernel weight (g) |
Kernel yield (t ha-1) |
Normal kernels (%) |
||||||
|
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
2010 |
2011 |
||
|
PS1 |
CP1 |
12.2l |
11.4k |
11.2m |
10.8k |
13.7h |
13.6i |
2.0n |
1.9m |
67.79m |
66.18m |
|
|
CP2 |
25.8d |
25.4d |
40.4d |
36.3e |
23.0bc |
22.3a-d |
5.2c |
5.1c |
78.11e |
76.21d |
|
|
CP3 |
22.6f |
22.0f |
30.9g |
27.6g |
21.2de |
20.8c-e |
4.6e |
4.4f |
76.08g |
74.31fg |
|
|
CP4 |
18.7h |
18.0h |
21.3i |
19.4i |
19.3f |
18.9ef |
3.9h |
3.7h |
73.34i |
72.21i |
|
|
CP5 |
15.4j |
14.8j |
15.5jk |
12.8jk |
16.6g |
12.6i |
2.9k |
2.8j |
70.46k |
69.26k |
|
|
CP1 |
27.8c |
26.8c |
48.4c |
45.6d |
23.6ab |
23.4ab |
5.4b |
5.3bc |
79.33d |
77.41c |
|
PS2 |
CP2 |
12.4kl |
11.9k |
12.9lm |
12.4jk |
14.4h |
14.1hi |
2.3m |
2.2l |
68.69l |
67.11lm |
|
|
CP3 |
29.3b |
28.0b |
52.0b |
47.7cd |
24.1ab |
23.7a |
5.4b |
5.3b |
79.91cd |
78.12bc |
|
|
CP4 |
24.4e |
23.7e |
33.3f |
31.6f |
21.9cd |
21.3b-e |
4.8d |
4.7e |
76.73fg |
74.70ef |
|
|
CP5 |
20.3g |
19.5g |
24.8h |
22.2hi |
19.9ef |
19.5e |
4.1g |
4.0g |
74.23h |
72.79hi |
|
|
CP1 |
16.0ij |
15.5ij |
16.0j |
11.0k |
16.9g |
16.4f-h |
3.1j |
3.0i |
71.29j |
70.18jk |
|
|
CP2 |
30.0ab |
29.1ab |
53.8a |
51.8ab |
24.3ab |
23.7a |
5.6a |
5.6a |
80.74ab |
78.55ab |
|
PS3 |
CP3 |
13.5k |
12.4k |
13.8kl |
12.9jk |
15.0h |
14.4g-i |
1.8n |
1.8m |
69.34l |
67.75l |
|
|
CP4 |
30.8a |
28.3b |
54.4a |
50.2bc |
24.5a |
22.5a-c |
5.1c |
4.8e |
80.49bc |
78.70ab |
|
|
CP5 |
24.8de |
24.0e |
35.4e |
33.6ef |
22.2cd |
19.7e |
4.4f |
4.2f |
77.33f |
75.36de |
|
|
CP1 |
21.1g |
19.9g |
26.6h |
22.9h |
20.3ef |
19.9de |
3.7i |
3.6h |
74.80h |
73.42gh |
|
|
CP2 |
16.8i |
16.0i |
17.1j |
15.1j |
17.2g |
16.7fg |
2.8l |
2.5k |
71.89j |
70.74j |
|
|
CP3 |
30.9a |
30.0a |
55.8a |
53.4a |
24.7a |
23.8a |
5.3b |
5.2cd |
81.37a |
79.13a |
|
LSD value at 5% |
1.16 |
1.08 |
1.98 |
3.15 |
1.39 |
2.51 |
0.14 |
0.14 |
0.749 |
0.943 |
|
The
means following the same letters, within a column for each trait, did not
significantly differ at 5% probability level
Plant
spacing (PS1= 20 cm ×20 cm, PS2= 25 cm ×25 cm, PS3=
30 cm × 30 cm); Weed crop competition periods (CP1= weedy
check/control, CP2= 20 DAT (Days after transplanting), CP3=
40 DAT, CP4= 60 DAT, CP5= 80 DAT, CP6= weed
free)
Narrowing the crop row spacing in rice is known as a
significant component of integrated weed management system as it results in
reduced weed infestation and higher crop yields (Ali et al. 2019). By extending the weed
competition period in rice, weed density and dry weight tend to increase (Bajwa et al.
2020). In the present studies, significant difference in weed density existed
among different transplant spacing in rice and competition periods of weed
during two years of experimental study and the significant increase in weed
density occurred by widening the row spacing of rice crop. It was probably due
to fact that wider spacing allowed the more growing area accessible for the
growth of weed plants. While the weed density was restricted by the narrow
spacing because transplantation of rice plants in close to each other won the
utilization race of resources from the neighbouring weed plants by using most
of growing land as compared to the weeds for their growth. By increasing
competition period, weed density was increased due to more availability of time
for germination of weeds from soil weed seed bank. Similarly, weed dry biomass
also showed an increasing trend in response to rise in rice transplant spacing
and competition period of weed plants while significant reduction in weed dry
weight was caused with the decreased rice plant spacing. That reduction in dry
weight was the result of increased severity in competition imposed on weeds by
rice crop due to leaving very less space for weed flourishment. While under
wider plant spacing, weed germination, growth and development was enhanced due
to more space available for weeds (Table 1). Ali et al. (2019) also reported that weed dry biomass was diminished
with decline in inter row spacing. Increase in weed dry biomass by prolongation
in weed competition period was obviously due to more availability of
germination time for weed and its growth and development. As strong positive
correlation between crop row spacing and weed competition period in rice was
shown by Chauhan and Johnson (2011). They concluded that wider row spacing of
rice prolonged weed competition period that resulted in significant increase in
weed density and dry biomass. Ashraf et
al. (2014) recorded significant decline in weed density and biomass by
imposing closer planting geometry in puddled rice. A gradual enhancement in
density and dry biomass of weeds in response to increasing weed competition
duration in rice was also documented by Matloob et al. (2015).
%201142-1148_files/image004.png)
Fig. 2: Relationship between competition period and total weed
dry biomass in rice under system of rice intensification as affected by
competition period during 2010 and 2011
The rice root growth in terms of higher root mass and
root length suffered from significant decline in response to extended weed
competition period which was attributed to higher root density and dry weight
under prolonged weed competition period. However,
narrowing the crop row spacing resulted in higher intra-specific competition
between rice plants that caused rice root growth inhibition. Consequently,
significantly reduced root biomass and root length of rice plants were noted in
narrow crop spacing and significant linear reductions in count of fertile
tillers hill-1, 1000-kernal weight, normal kernel percentage, and
rice kernel yield were observed as weed competition period was increased from 0
to 80 days after transplanting (Table 2). This declining response of number of
tillers of rice to prolonged weed competition was probably owed to increased
weed competition stress faced by rice crop that suppressed its tiller
production. In the same way, narrower plant spacing of rice aggravated the
intra-specific competition stress among rice plants that reduced its number of
tillers hill-1. Juraimi et al.
(2009) reported that with increase in competition period, decline in rice
tillers occurred. In weed free conditions, rice transplant spacing of 20 cm
attained the maximum normal kernel percentage. However, under weedy conditions,
there was significant increase in normal kernel percentage of rice in by
widening crop transplant spacing from 20 to 25 cm beyond this no significant
increase in normal kernel percentage was recorded showing that 25 cm plant
spacing is best for this parameter. Our results are in line with the outcomes
of Vijayakumar et al. (2006) who
obtained maximum number of kernels per panicle when plant spacing was 25 cm ×
25 cm and Salahuddin et al. (2009)
who also obtained higher number of kernels per panicle when spacing between plants
was 20 cm × 20 cm. Nandal and Singh (1995) reported that with the increase in
competition duration with weed resulted in less number of normal kernel
percentage. Significantly the higher kernel yields of rice in all competition
periods of weed were achieved in response to transplant spacing of 25 × 25 cm.
However, plant spacing narrower or wider than it produced lower kernel yields
of rice. The maximum kernel yield of rice at 25 × 25 cm plant spacing appears
to be because of higher 1000-grain weight and normal kernel percentage, the two
important yield contributing traits observed with this plant spacing. Our
results are similar to findings of Vijayakumar et al. (2006) who obtained the maximum rice kernel yield when plant
spacing was 25 × 25 cm. Our results are in contrary to those of some of the
researchers (Kumar et al. 2019; Saju et al. 2019; Verma et al. 2019) who found narrower plant spacing to be more
advantageous in gaining higher kernel yield of puddled rice. One the reasons of
this contradiction seems to be the agro-climatic and rice genotypic differences
as varieties used in those studies were non-basmati coarse grain rice.
Conclusion
It is concluded that under the agro-environmental conditions of
Punjab-Pakistan, the best transplant spacing for Super Basmati rice is 25 cm ×
25 cm and critical weed competition period is 20 days after transplanting
(DAT). Therefore, a weed management strategy must be employed within this
period to obtain the maximum yield from Basmati rice under the system of rice
intensification (SRI).
Author Contributions
ARC
and MAN planned the research experiments, HHA, MES and MSK interpreted the
results, ARC, AR, MA and MH made the write-up, MMJ statistically analyzed the data and LA reviewed the whole manuscript
grammatically and technically.
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