Wee mangmnt

ARTICLE IN PRESS
Crop Protection 27 (2008) 660–671
www.elsevier.com/locate/cropro
Weed management in aerobic rice systems under varying
establishment methods
Samar Singha, J.K. Ladhab,,1, R.K. Guptaa, Lav Bhushana, A.N. Raob,2
aRice–Wheat Consortium for the Indo-Gangetic Plains, CIMMYT-India, CG Block, NASC Complex, DPS Marg, New Delhi 110 012, India
bInternational Rice Research Institute (IRRI), India Office, 1st Floor, CG Block, NASC Complex, DPS Marg, New Delhi 110 012, India
Received 24 September 2007; accepted 25 September 2007
Abstract
Aerobic rice systems, wherein the crop is established via direct-seeding in non-puddled, non-flooded fields, are among the most
promising approaches for saving water and labour. However, aerobic systems are subject to much higher weed pressure than
conventionally puddled transplanted rice (CPTR). Experiments were conducted for 2 years to develop effective and economical methods
for managing weeds in aerobic rice grown by direct-seeding or transplanting on flat land or furrow-irrigated raised-bed systems (FIRBS).
Total weed dry weight and weed density were lower with CPTR and highest with aerobic direct-seeded rice on a FIRBS (ADSB),
followed by aerobic direct-seeded rice (ADSR). In terms of weight grassy weed constituted 78–96% of total weed weight in all systems of
rice establishment. Loss of grain yield of rice due to weed competition ranged from 38% to 92%, being the highest in ADSB. Both weed
density and dry weight were negatively correlated with rice grain yield. ADSR treatment produced yield and net economic returns similar
to CPTR treatment when weeds were controlled. Pretilachlor with safener at 500 g a.i. ha1 applied 3 days after sowing (DAS)/ days after
transplanting (DAT) followed by chlorimuron+metsulfuron at 4 g a.i. ha1 applied 21 DAS/DAT followed by hand-weeding at 35 DAS/
DAT could effectively control all the weeds. The next best treatment was cyhalofop-butyl at 120 g a.i. ha1 applied 14 DAS/DAT
followed by chlorimuron+metsulfuron at 4 g a.i. ha1 applied 21 DAS/DAT followed by hand-weeding at 35 DAS/DAT. The ADSR
was as effective as conventionally puddle-transplanted rice in attaining higher rice grain yield and net returns when weeds were kept
under control.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: Chlorimuron+metsulfuron; Cyhalofop-butyl; Pretilachlor with safener; Aerobic rice; Oryza sativa L.; Establishment methods; Economic weed
management
1. Introduction
The rice–wheat system, occupying 24 million hectares of
productive area in South Asia and China, is important for
food security of the region (Ladha et al., 2003). The annual
productivity of the rice–wheat system in the Indo-Gangetic
Plains (IGP) is low (3–5Mgha1) compared with the
climatic yield potential of the region (12–19.3Mgha1)
(Aggarwal et al., 2000; Pathak et al., 2003). In high-productivity
zones of the IGP, the rice–wheat system is
stressed due to production fatigue as evidenced by
declining soil organic matter content, low fertilizer use
and diminishing rates of factor productivity (Dwivedi
et al., 2003; Ladha et al., 2003). Transplanting in puddled
soils (wet tillage), with continuous flooding, is the most
common method of rice crop establishment. Transplanted
rice requires a large amount of water and labour. During
peak periods of transplanting, labour also becomes very
scarce. Puddling also affects soil health due to the
dispersion of soil particles, soil becoming compact and
making tillage operations difficult requiring more energy in
succeeding crops such as wheat (Singh et al., 2002).
Fujisaka et al. (1994), on the basis of a diagnostic survey
Corresponding author. Tel.: +9111 25843802; fax: +9111 25841801.
E-mail addresses: j.k.ladha@cgiar.org (J.K. Ladha),
anraojaya@hotmail.com (A.N. Rao).
1Present address: Department of Crop and Soil Sciences, Cornell
University, Ithaca, NY 14853, USA.
2Present address: Plot 1294A, Road 63A, Jubilee Hills, Hyderabad 500
033, India.
0261-2194/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cropro.2007.09.012

ARTICLE IN PRESS
S. Singh et al. / Crop Protection 27 (2008) 660–671 661
conducted in several rice–wheat areas in South Asia,
observed low wheat yields in a rice–wheat system, mainly
due to deterioration in soil structure and the development
of subsurface hardpans. Hobbs et al. (2002) described the
emerging issues of sustainability of rice–wheat systems and
stressed the need to improve water-use efficiency, soil
structure and weed management against the backdrop of
increasing labour and water scarcity. An alternative to
puddling and transplanting of rice could be aerobic direct-seeding
because it requires less water, labour and capital
input. The direct-seeded crop also matures earlier (7–10
days) than the transplanted crop, thus allowing timely
planting of the succeeding wheat crop (Giri, 1998; Singh
et al., 2006).
Irrigated ‘‘aerobic rice’’ is a new system being developed
for lowland areas with water shortage and for favourable
upland areas with access to supplementary irrigation
(Tuong and Bouman, 2003; Belder et al., 2005). Aerobic
rice systems, wherein the crop is established via direct-seeding
in non-puddled, non-flooded fields, are among the
most promising approaches for saving water (Wang et al.,
2002; Tuong and Bouman, 2003; Bhushan et al., 2007).
Aerobic rice systems can reduce water application by 44%
relative to conventionally transplanted systems, by redu-cing
percolation, seepage and evaporative losses, while
maintaining yield at an acceptable level (6Mgha1) (Wang
et al., 2002; Bouman et al., 2005). However, aerobic
systems are subject to much higher weed pressure than
conventional puddled transplanting systems (Rao et al.,
2007; Balasubramanian and Hill, 2002) in which weeds are
suppressed by standing water and by transplanted rice
seedlings, which have a ‘‘head start’’ over germinating
weed seedlings (Moody, 1983). Aerobic soil dry-tillage and
alternate wetting and drying conditions, on the other hand,
are conducive to the germination and growth of weeds
causing grain yield losses of 50–91% (Elliot et al., 1984;
Fujisaka et al., 1993; Rao et al., 2007). Thus, weeds are the
most severe constraints to aerobic rice production and
timely weed management is crucial to increasing the
productivity of aerobic rice (Rao et al., 2007).
Studies in northern Australia (Garside et al., 1992) and
Indonesia (Van Cooten and Borrell, 1999) found that rice
can be successfully rotated with upland crops using
saturated soil culture on permanent raised beds. Advan-tages
identified with this system of rice production under
saturated soil culture on permanent beds include water,
nitrogen and phosphorus economies, energy savings,
greater timeliness of field operations and a reduction in
soil compaction (Borrell and Garside, 2005). Farmers’ and
researchers’ trials in the IGP suggest irrigation water
savings of 12–60% for direct-seeded or transplanted rice on
flat or raised beds, but with some yield penalty (Gupta
et al., 2000). As the bed is often under aerobic conditions,
growth of weeds, especially grasses, is promoted, posing a
problem in the raised-bed system (Singh et al., 2006).
Most upland and aerobic rice growers in Asia mechani-cally
weed their crops two or three times per season,
investing up to 190 person days ha1 in hand-weeding
(Roder, 2001). The labour requirement for weeding is a
major impediment to the adoption of water-saving aerobic
rice, and to increasing the productivity of aerobic rice-based
cropping systems. Herbicides are considered to be an
alternative/supplement to hand-weeding (Singh et al.,
2006). Both pre-emergence and post-emergence herbicides
can be used in aerobic rice fields, and they are effective, if
properly used (De Datta and Baltazar, 1996; Singh et al.,
2006). Chemical weed control on puddled flat lands was
good but in case of transplanted rice on beds 1–2 hand-weedings
were required, which increased to 3–4 in direct-seeded
rice on beds (Kukal et al., 2005).
Information on weeds and weed management in aerobic
rice cultivated on flat land and on raised beds, by either
transplanting or direct-seeding, is scarce. Since the concept
of aerobic rice is new (Tuong and Bouman, 2003; Belder et
al., 2005), growing rice under aerobic conditions on raised
beds or on flat land would require suitable, effective and
economical weed-control methods. Development of new
improved herbicides for aerobic dry-seeded rice is also
needed (Gupta et al., 2003). The present experiment was
conducted to develop effective and economical methods for
managing weeds in aerobic rice grown by direct-seeding or
transplanting on flat land or furrow-irrigated raised-bed
systems (FIRBS) and comparing it with conventional
flooded puddled transplanted rice.
2. Materials and methods
2.1. Experimental site
The field experiment was conducted for 2 years (2002
and 2003) at the experimental farm of the Sardar Vallab
Bhai Patel University of Agriculture and Technology,
Modipuram, Meerut, Uttar Pradesh, India (29140N and
771460E, at an elevation of 237m above mean sea level).
The climate of Modipuram is broadly classified as semi-arid
subtropical, characterized by very hot summers and
cold winters. The hottest months are May and June, when
the maximum temperature reaches 45–46 1C, whereas
during December and January, the coldest months of the
year, the minimum temperature often goes below 5 1C. The
average annual rainfall is 863 mm, 75–80% of which is
received through the northwest monsoon during July–
September. The experimental soil was silty loam in texture
with particle density 2.65Mgm3, mean weight diameter of
soil aggregates 0.71mm indicating a poorly developed soil
structure, mainly because the soil reclaimed recently was
alkaline (sodic) in nature. The soil (0–15 cm) retained 18%
and 7% moisture (mass basis) at 30 and 1500 kPa suction,
respectively, with plant-available water capacity of 11%.
The soil reaction was alkaline, with very low salt content.
The surface soil (0–15 cm) had 0.83% total carbon, 0.088%
total N, 25 mg kg1 Olsen’s P and 0.314 meq 100 g1 1N
NH4OAC-extractable K. DTPA-extractable Zn, Cu, Fe
and Mn were in the high range in the surface soil layer.

662 S. Singh et al. / Crop Protection 27 (2008) 660–671
2.2. Experimental design and treatments
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The experiment was arranged in a split-plot design with
three replications. The four treatments (see Table 1)
assigned to the main plot were (a) aerobic direct-seeded
rice on FIRBS (ADSB), (b) aerobic direct-seeded rice on
flat land (ADSR), (c) aerobic transplanted rice on FIRBS
(ATPB) and (d) conventionally puddled transplanted rice
(CPTR). The rice was direct-seeded at 40 kg ha1 at 20-cm
row spacing using a tractor-drawn zero-till seed machine-cum-
fertilizer drill in zero-till conditions for direct-seeded
rice on flat land. The size of subplots was 10m5.4 m.
Five weed-control treatments (see Table 1) were assigned to
the subplots: (a) weedy; (b) weed-free; (c) cyhalofop-butyl
(at 120 g a.i. ha1 applied 14 DAS/DAT) followed by 2,4-D
(ester) (at 500 g a.i. ha1 applied 21 DAS/DAT) followed by
hand-weeding at 35 DAS/DAT (referred as cyhalofop-butyl/
2,4-D/HW); (d) cyhalofop-butyl (at 120 g a.i. ha1
applied 14 DAS/DAT) followed by chlorimuron+metsul-furon
(at 4 g a.i. ha1 applied 21 DAS/DAT) followed by
hand-weeding at 35 DAS/DAT (referred as cyhalofop-butyl/
chlorimuron+metsulfuron/HW) and (e) pretilachlor
with safener (at 500 g a.i. of pretilachlor ha1 applied
3 DAS/DAT) followed by chlorimuron+metsulfuron (at
4 g a.i. ha1 applied 21DAS/DAT) followed by hand-weeding
at 35DAS/DAT (referred as pretilachlor/chlor-imuron+
metsulfuron/HW). Herbicides were applied using
a knapsack sprayer with a flat fan nozzle and water as a
carrier at 300 l ha1. For the weed-free subplot treatment,
six hand-weedings were done to maintain a weed-free
situation. In the weedy control, no weeding was done.
2.3. Experimental details and measurements
Rice (cv. NDR 359, a medium-long-duration variety)
was planted in June and harvested in October in each year.
For ADSB and ATPB main-plot treatments, land was
prepared with two ploughings with a disc harrow and one
planking. After preparation of the field, beds 37 cm wide
with a furrow of 30 cm were formed with the help of a
tractor-drawn bed planter (Bhushan et al., 2007). In ADSB
treatment, seed at 30 kg ha1 was direct-seeded in two rows
at 25-cm spacing using a tractor-drawn bed planter. After
germination of rice, all plots were submerged for a week.
Later, irrigation was applied to maintain soil saturation for
a month, which was followed by irrigation at an interval of
4–5 days. In the ATPB treatment, manual transplanting
was done at one seedling per hill in two rows at 20-cm
spacing with 12 cm for plant-to-plant spacing. For direct-seeded
rice on flat land (ADSR) in the main-plot treatment,
the pre-seeding herbicide glyphosate was applied 2 days
before seeding in zero-till conditions to kill already
germinated weeds and seeding (40 kg ha1) was done on
flat land using a tractor-mounted zero-till seed-cum-fertilizer
drill keeping 25 cm of distance between rows.
Irrigation was applied after seeding. Soil saturation was
maintained for a month and later irrigation was given at an
interval of 4–5 days. The land preparation for the CPTR
main plot treatment consisted of one dry ploughing
followed by irrigation and two harrowings to puddle the
soil under wet conditions. Two rice seedlings per hill were
transplanted at 20 cm20 cm spacing after puddling.
Nitrogen was applied at 150 kg ha1 in three equal splits
as basal, at 20 DAT/42DAS and at 45 DAT/65 DAS.
Phosphorus at 60 kg ha1 as P2O5 in the case of direct-seeded
rice on flat land and in raised beds was applied with
a zero-till drill (ZT) during seeding. For transplanted rice,
it was broadcast at the time of transplanting. Potash at
60 kg ha1 as K2O and zinc at 25 kg ha1 as ZnSO4
were broadcast in all plots uniformly before rice sowing/
transplanting.
Weed density and weed dry weight were measured at 30,
60 and 120 DAS/DAT. Weed density was recorded with the
help of a quadrate (0.5m0.5 m) placed randomly at two
spots in each plot. Weeds were cut at ground level, washed
with tap water, sun dried, oven dried at 70 1C for 48 h and
then weighed. The data on actual number of weeds were
transformed by angular transformation for statistical
analyses. Grain yield was taken from a 6-m2 area in the
centre of each plot and expressed in Mgha1 at 14%
moisture. The statistical analysis of the data was done
using IRRISTAT Windows Version 4.1. Unless indicated
otherwise, differences were considered significant only at
Pp0.05.
3. Results and discussion
The major weeds associated with rice include grasses
Dactyloctenium aegyptium (L.) Willd., Echinochloa crus-galli
(L.) Beauv., Echinochloa colona (L.) Link and Leptochloa
chinensis (L.) Nees, and broadleaf weeds Commelina
benghalensis L., Caesulia axillaris Roxb., Eclipta prostrata
(L.) L., Euphorbia hirta L., Portulaca oleracea L., Trianthema
portulacastrum L. and Lindernia sp.
The total weed dry weight (Table 1) and total weed
density (Table 2) were lower with CPTR at all stages of
crop growth in both years. It is reported that the greatest
weed pressure and crop–weed competition occur in upland
and aerobic rice and least in transplanted irrigated and
rainfed lowland rice (De Datta and Baltazar, 1996;Moody,
1996; Rao et al., 2007). During both years, the proportion
of grassy weed dry weight was higher (78–96% of total
weed dry weight in 2002 and 82–89% in 2003) than for
other weeds in all systems of rice establishment. Grasses
persist in all of the principal crops and are a major cause
for concern (Mortimer and Riches, 2001). The proportion
of mean grassy weed dry weight (Table 3) in ADSB
(93–96% of total weed biomass) and ADSR (92–96% of
total weed biomass) was higher than that recorded with
ATPB (78–93% of total weed biomass) and CPTR
(82–93% of total weed biomass) systems of rice establish-ment
during 2002. The ADSB treatment resulted in the
highest total weed dry weight at all stages of crop growth
during both years. The next highest weed dry weight was

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Table 1
Impact of varying methods of rice establishment and weed control treatments on total weed dry weight (gm2)
Weed control method (W)a Method of rice establishment (T)b
ADSB ADSR ATPB CPTR Mean
30DAS 60DAS 120DAS 30DAS 60DAS 120DAS 30DAT 60DAT 120DAT 30DAT 60DAT 120DAT 30DAS/DAT 60 DAS/DAT 120 DAS/DAT
Year 2002
Cyhalofop/2,4-D/HW 16.1 107.9 184.3 10.6 60.3 145.1 4.2 19.2 43.0 2.7 11.6 19.5 8.4 49.8 98.0
Cyhalofop/chlorimuron+metsulfuron/HW 16.2 89.3 190.3 9.9 57.1 137.6 4.9 18.7 37.8 2.2 11.5 15.9 8.3 44.2 95.4
Pretilachlor/chlorimuron+metsulfuron/HW 8.8 73.9 143.2 3.8 36.7 87.5 1.8 9.3 25.0 1.3 4.8 13.0 4.0 31.2 67.2
Weedy treatment 27.3 270.6 441.0 17.3 153.7 285.4 6.7 111.8 256.7 4.7 70.6 152.7 14.0 151.7 283.9
Mean 13.8 108.4 191.9 8.4 61.7 131.2 3.6 31.9 72.6 2.2 19.8 40.3
LSD (p ¼ 0.05) for comparison:
Of two T means at each W 2.8 27.1 27.9
Of two W means at each T 2.5 25.3 25.3
T means 1.7 15.1 16.4
W means 1.2 12.6 12.7
Year 2003
Cyhalofop/2,4-D/HW 19.0 91.6 140.5 13.9 78.1 150.6 13.1 62.3 108.5 6.2 34.4 57.6 13.0 66.6 114.3
Weedy treatment 34.1 263.3 348.8 27.8 202.1 285.6 24.3 136.8 224.5 12.0 81.7 130.4 24.6 171.0 247.3
Mean 17.7 99.1 144.5 12.5 79.1 130.3 12.0 57.3 100.4 5.6 30.5 52.8
T means 1.77 16.0 13.3
W means 1.67 14.4 15.1
aCyhalofop/2,4-D/HW ¼ cyhalofop (at 120 g a.i. ha1 applied 14DAS/DAT) followed by 2,4-D (at 500 g a.i. ha1 applied 21DAS/DAT) followed by hand-weeding at 35DAS/DAT, cyhalofop/
chlorimuron+metsulfuron/HW ¼ cyhalofop (at 120 g a.i. ha1 applied 14DAS/DAT) followed by chlorimuron+metsulfuron (at 4 g a.i. ha1 applied 21DAS/DAT) followed by hand-weeding at
35DAS/DAT, pretilachlor/chlorimuron+metsulfuron/HW ¼ pretilachlor with safener (at 500 g a.i. ha1 applied 3DAS/DAT) followed by chlorimuron+metsulfuron (at 4 g a.i. ha1 applied 21 DAS/
DAT) followed by hand-weeding at 35DAS/DAT.
bADSB ¼ aerobic direct-seeded rice on furrow-irrigated raised-bed system (FIRBS); ADSR ¼ aerobic direct-seeded rice; ATPB ¼ aerobic transplanted rice on FIRBS; CPTR ¼ conventionally
puddled transplanted rice; DAS ¼ days after seeding; DAT ¼ days after transplanting.

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Table 2
Impact of varying methods of rice establishment and weed control treatments on total weed density (numberm2)
30DAS 60DAS 120DAS 30DAS 60DAS 120DAS 30DAT 60DAT 120DAT 30DAT 60DAT 120DAT 30 DAS/
DAT
60DAS/
DAT
120 DAS/
DAT
Year 2002
Cyhalofop/2,4-D/HW 183 133 120 111 92 93 138 102 93 61 46 37 123 93 85
(13.5) (11.6) (11.0) (10.5) (9.6) (9.7) (11.8) (10.1) (9.7) (7.8) (6.8) (6.2) (10.9) (9.5) (9.1)
Cyhalofop/chlorimuron+metsulfuron/HW 171 127 113 101 81 83 129 89 83 61 45 29 116 85 76
(13.1) (11.3) (10.7) (10.1) (9.0) (9.1) (11.4) (9.5) (9.1) (7.8) (6.8) (5.4) (10.6) (9.1) (8.5)
Pretilachlor/chlorimuron+metsulfuron/
HW
115 110 99 57 67 55 44 52 55 22 19 16 60 62 59
(10.8) (10.5) (10.0) (7.6) (8.2) (7.5) (6.7) (7.2) (7.5) (4.8) (4.4) (4.1) (7.5) (7.6) (7.4)
Weedy treatment 314 392 368 196 243 252 224 301 252 135 179 191 217 279 273
(17.7) (19.8) (19.2) (14.0) (15.6) (15.9) (15.5) (17.4) (15.9) (11.7) (13.1) (13.9) (14.6) (16.5) (16.4)
Mean 157 152 140 93 97 97 107 109 97 56 58 55
(11.2) (10.8) (10.4) (8.7) (8.7) (8.6) (9.2) (9.0) (8.6) (6.6) (6.5) (6.1)
LSD (p ¼ 0.05) for comparison:c
T means 1.7 0.8 0.7
W means 1.2 0.7 0.4
Year 2003
Cyhalofop/2,4-D/HW 125 150 111 85 149 147 79 103 80 48 59 57 84 115 99
(11.2) (12.3) (10.6) (9.3) (12.2) (12.1) (8.9) (10.2) (9.0) (7.0) (7.7) (7.6) (9.1) (10.6) (9.8)
(10.6) (12.1) (9.5) (9.0) (11.7) (10.8) (8.5) (9.7) (8.0) (6.4) (7.4) (6.6) (8.6) (10.2) (8.7)
HW
80 112 74 57 79 69 39 79 49 17 28 23 48 74 54
(9.0) (12.6) (8.6) (7.5) (8.9) (8.3) (6.3) (8.9) (7.1) (4.3) (5.4) (4.8) (6.8) (8.4) (7.2)
Weedy treatment 286 373 305 233 299 264 167 222 184 96 112 92 196 251 211
(16.9) (19.3) (17.5) (15.3) (17.3) (16.2) (13.1) (14.9) (13.6) (9.8) (10.6) (9.6) (13.8) (15.5) (14.2)
Mean 120 156 116 91 133 119 71 100 75 40 50 43
(9.4) (11.1) (9.4) (8.4) (10.2) (9.7) (7.5) (8.9) (7.7) (5.7) (6.4) (5.9)
T means 0.83 0.62 0.56
W means 0.65 0.63 0.61
aAs in Table 1.
cCalculated using transformed values given in parentheses.

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Table 3
Impact of varying methods of rice establishment and weed control treatments on grassy weed dry weight (gm2)
30DAS 60DAS 120DAS 30DAS 60DAS 120DAS 30DAT 60DAT 120DAT 30DAT 60DAT 120DAT 30DAS/DAT 60 DAS/DAT 120 DAS/DAT
Year 2002
Cyhalofop/2,4-D/HW 15.2 105.0 176.3 10.2 57.9 137.3 3.8 17.4 38.8 2.3 10.6 16.1 7.9 47.7 92.2
Weedy treatment 24.9 262.2 420.4 15.4 147.2 272.0 4.9 104.8 240.2 3.6 66.1 141.8 12.2 145.1 268.6
Mean 12.8 105.1 183.4 7.7 59.1 124.7 2.8 29.7 67.2 1.8 18.5 36.3
T means 1.5 15.4 16.6
W means 1.2 13.0 13.1
Year 2003
Cyhalofop/2,4-D/HW 15.8 79.3 124.9 11.8 69.0 131.0 11.5 56.1 96.4 5.3 30.5 50.5 11.1 58.7 100.7
Weedy treatment 27.8 229.7 303.9 22.8 171.8 247.6 20.9 119.9 197.5 9.8 75.2 119.0 20.3 149.2 217.0
Mean 14.7 86.8 128.0 10.4 68.5 114.1 10.1 51.0 89.0 4.6 27.0 47.0
T means 1.5 15.6 11.1
W means 1.6 13.4 14.4
aAs in Table 1.

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Table 4
Impact of varying methods of rice establishment and weed control treatments on grass weed density (numberm2)
30DAS 60DAS 120DAS 30DAS 60DAS 120DAS 30DAT 60DAT 120DAT 30DAT 60DAT 120DAT 30 DAS/
DAT
60DAS/
DAT
120 DAS/
DAT
Year 2002
Cyhalofop/2,4-D/HW 155 110 90 97 75 74 124 85 71 54 37 31 108 77 66
(12.4) (10.5) (9.5) (9.9) (8.6) (8.6) (11.1) (9.2) (8.5) (7.4) (6.1) (5.6) (10.2) (8.6) (8.1)
(12.8) (10.6) (9.8) (9.7) (8.2) (8.5) (11.0) (8.8) (8.2) (7.4) (6.2) (5.0) (10.2) (8.4) (7.9)
HW
76 85 75 29 49 43 18 39 50 4 8 9 32 45 45
(8.8) (9.2) (8.7) (5.5) (7.1) (6.6) (4.3) (6.3) (7.2) (2.2) (3.0) (3.2) (5.2) (6.4) (6.4)
Weedy treatment 252 320 291 161 195 191 174 245 231 109 143 138 174 226 213
(15.8) (17.8) (17.1) (12.7) (13.9) (13.8) (13.2) (15.6) (15.2) (10.5) (12.0) (11.8) (13.0) (14.8) (14.5)
Mean 129 125 110 76 77 76 87 89 84 44 45 40
(10.2) (9.8) (9.2) (7.8) (7.8) (7.7) (8.1) (8.2) (9.1) (5.7) (5.7) (5.3)
T means 1.7 0.8 0.7
W means 1.2 0.7 0.4
Year 2003
Cyhalofop/2,4-D/HW 80 79 56 53 83 61 51 66 42 29 39 32 53 66 48
(9.0) (8.9) (7.5) (7.3) (9.1) (7.9) (7.2) (8.1) (6.6) (5.5) (6.3) (5.7) (7.3) (8.1) (6.9)
(9.0) (9.0) (7.3) (7.5) (8.6) (7.7) (7.1) (7.5) (6.0) (5.1) (5.5) (5.0) (7.2) (7.7) (6.5)
HW
56 61 43 24 32 59 21 40 27 7 5 24 27 35 26
(7.5) (7.9) (6.6) (5.0) (5.7) (5.5) (4.6) (6.4) (5.2) (2.7) (2.5) (5.0) (5.0) (5.6) (5.0)
Weedy treatment 146 194 169 112 147 128 99 130 109 56 77 55 103 137 115
(12.1) (13.9) (13.0) (10.6) (12.1) (11.3) (10.0) (11.4) (10.5) (7.5) (8.8) (7.4) (10.1) (11.6) (10.6)
Mean 72 83 64 49 67 55 44 58 43 23 30 24
(7.7) (8.1) (7.1) (6.3) (7.3) (6.7) (6.0) (6.9) (5.9) (4.4) (4.8) (5.0)
T means 0.52 0.25 0.38
W means 0.53 0.46 0.55
aAs in Table 1.
puddled transplanted rice;DAS ¼ days after seeding; DAT ¼ days after transplanting.
cCalculated using transformed values given in parentheses.

ARTICLE IN PRESS
observed with aerobic direct-seeded rice (ADSR). In
contrast, Meisner et al. (2005) reported fewer weeds in
rice with permanent raised beds. Promotion of the growth
of grassy weeds in the raised-bed system was reported by
Cabangon and Tuong (2005). In 2002, the proportion of
grassy weed density ranged from 73% to 79% of total weed
density in CPTR, whereas in other systems of planting rice
it ranged from 78% to 82% (Table 4). In 2003, such
variation among establishment methods was not observed
and the proportion of grassy weeds ranged from 46% to
60% of the total weed density under different establish-ment
methods.
During both years, pretilachlor/chlorimuron+metsul-furon/
HW treatment resulted in significantly lower mean
total weed dry weight than other chemical weed control
treatments (Table 1). Pretilachlor/chlorimuron+metsul-furon/
HW treatment resulted in a 68%, 73% and 67%
reduction in weed dry weight at 30, 60 and 120 DAS/DAT,
respectively, in 2002 and 57%, 78% and 69% reduction in
2003. The weed dry weight with cyhalofop-butyl/chlor-imuron+
metsulfuron/HW and cyhalofop-butyl/2,4-D/
HW treatments did not differ among each other. Cyhalo-fop-
butyl was reported to be effective on Echinochloa
species (Barotti et al., 1998) and other grasses (Buendia
et al., 1998) that were predominant in the trials. With all
methods of rice establishment, the reduction in total weed
dry weight and grassy weed dry weight was higher at
60 DAS/DAT and the efficacy of all the chemicals at
120 DAS/DAT was lower than that recorded at 60 DAS/
DAT. The reduction in efficacy at 120DAT was lowest
with CPTR. Irrespective of the stage of crop growth and
type of weed group, a significant negative correlation of
weed density and weed dry weight with rice grain and straw
yield was observed (Table 5), indicating the need for
minimizing weed density and dry weight to attain optimal
rice grain yield.
The highest rice grain yield was recorded with the CPTR
method of establishment during both years (Table 6). The
grain yield of ADSR was lower than that of CPTR as
reported by Singh et al. (2001). However, under weed-free
situations, the grain yield under these two methods of
establishment did not differ significantly, suggesting that
similar yield potential is achievable. Reddy and Panda
(1988) suggested that direct-seeded rice performed better
than a transplanted crop, while Mitchell et al. (2004)
indicated that direct-seeded rice and transplanted rice
will produce a similar yield for a given environment pro-vided
they are grown using good management practices.
Table 5
Correlation between weed density and dry weight at different days after seeding and rice grain and straw yield
Weed parameter Days after seeding Grain yield (Mg ha1) Straw yield (Mg ha1)
2002 2003 2002 2003
Total weed dry weight (gm2) 30 0.73
0.88
0.67
0.86
60 0.89
0.94
0.84
0.92
90 0.89
0.92
0.82
0.91
Grassy weed weight (gm2) 30 0.69
0.87
0.63
0.85
60 0.88
0.94
0.83
0.92
90 0.89
0.92
0.82
0.91
Broadleaf weed weight (gm2) 30 0.80
0.87
0.76
0.85
60 0.94
0.95
0.89
0.90
90 0.92
0.94
0.87
0.92
Sedge weed weight (gm2) 30 0.58
0.46
0.56
0.48
60 0.75
0.75
0.71
0.73
90 0.75
0.69
0.70
0.70
Total weed density (numberm2) 30 0.84
0.93
0.81
0.90
60 0.94
0.92
0.91
0.90
90 0.96
0.90
0.92
0.89
Grassy weed density (numberm2) 30 0.80
0.89
0.78
0.88
60 0.93 00.92
0.90
0.91
90 0.92
0.83
0.88
0.82
Broadleaf weed density (numberm2) 30 0.84
0.94
0.84
0.91
60 0.95
0.91
0.93
0.88
90 0.92
0.95
0.87
0.92
Sedge weed density (numberm2) 30 0.74
0.83
0.71
0.79
60 0.85
0.81
0.80
0.77
90 0.96
0.96
0.93
0.71
Significant at the 5% level.

ARTICLE IN PRESS
Table 6
Impact of varying methods of rice establishment and weed control treatments on rice grain and straw yield (Mg ha1)
The mean grain yield of aerobic dry-seeded rice on flat beds
(ADSR) and ATPB did not differ. The least mean grain
yield was recorded with ADSB. Many on-farm and on-station
trials in the IGP have also observed similar or
higher yields for transplanted rice and slightly lower yields
with direct-seeded rice on beds (Humphreys et al., 2004).
Choudhury et al. (2007) reported that rice yields on raised
beds that were kept around field capacity were 32–42%
lower than under flooded transplanted conditions. Beecher
et al. (2006) attributed the reduced grain yield from all bed
treatments to the wide furrows that were not planted with
rice and opined that, until an effective herbicide and
method of weed control are found, there is little scope for
saving water while maintaining yield through the use of
beds. Across establishment methods, 38–92% of grain yield
was lost where weeds were not controlled. Yield losses due
to uncontrolled weeds were highest with ADSB (92% in
2002 and 78% in 2003) and ADSR (88% in 2002 and 74%
in 2003) and lowest with CPTR (58% in 2002 and 38% in
2003). Among weed-control treatments, mean grain yield
data indicated that cyhalofop-butyl/chlorimuron+metsul-furon/
HW and pretilachlor/chlorimuron+metsulfuron/
HW treatments were similar to that of the weed-free
control in realizing higher yields during 2003. However,
during 2002, the weed-free control treatment was superior
to all weed-control treatments. Pretilachlor/chlorimur-on+
metsulfuron/HW application resulted in significantly
higher grain yield than other herbicide combinations tested
in 2002. Interactions between method of rice establishment
and weed control treatments were also significant during
both years. Under CPTR, rice grain and straw yield with
all weed control treatments were on par with each other
and were superior to that of the weedy check treatment.
The grain yield with pretilachlor/chlorimuron+metsulfur-on/
HW treatment was similar to that of the weed-free
control during both years. Pretilachlor/chlorimuron+met-sulfuron/
HW treatment yielded higher in ADSB than
with other chemical treatments only in 2002. The grain
Grain
yield
Straw
yield
Grain
yield
Straw
yield
Grain
yield
Straw
yield
Grain
yield
Straw
yield
Grain
yield
Straw
yield
Year 2002:
Cyhalofop/2,4-D/HW 4.99 4.83 6.12 6.21 5.79 5.29 6.63 5.74 5.88 5.52
Cyhalofop/chlorimuron+metsulfuron/
HW
4.92 4.91 6.20 6.37 5.92 5.32 6.66 5.75 5.92 5.58
HW
5.39 5.29 6.47 6.69 6.16 5.41 6.79 5.87 6.21 5.81
Weed-free treatment 5.82 5.43 6.75 6.90 6.73 5.79 6.82 5.82 6.53 5.98
Weedy treatment 0.48 1.45 0.8 2.28 2.12 2.85 2.90 3.41 1.57 2.50
Mean 4.32 4.38 5.27 5.69 5.34 4.93 5.93 5.32 5.22 5.08
Of two T means at each W 0.32 0.25
Of two W means at each T 0.31 0.28
T means 0.16 0.18
W means 0.16 0.12
Year 2003
Cyhalofop/2,4-D/HW 4.39 4.47 5.19 4.62 5.08 4.72 5.84 5.78 5.13 4.90
Cyhalofop/chlorimuron+metsulfuron/
HW
4.42 4.75 5.21 5.17 5.14 4.86 5.89 5.63 5.16 5.10
HW
4.53 4.72 5.44 4.96 5.25 5.03 5.99 5.95 5.30 5.16
Weed-free treatment 5.03 4.89 5.70 5.91 5.66 5.05 6.08 6.12 5.61 5.49
Weedy treatment 1.10 1.57 1.50 2.62 2.54 2.73 3.80 3.57 2.24 2.62
Mean 3.89 4.05 4.61 4.65 4.73 4.48 5.52 5.41
Of two T means at each W 0.48 0.77
Of two W means at each T 0.60 0.74
T means 0.43 0.29
W means 0.24 0.38
aAs in Table 1.
bADSB ¼ aerobic direct-seeded rice on furrow-irrigated raised-bed system (FIRBS); ADSR ¼ aerobic direct-seeded rice; ATPB ¼ aerobic transplanted
rice on FIRBS; CPTR ¼ conventionally puddled transplanted rice.

ARTICLE IN PRESS
Table 7
Net income (US$) as affected by varying methods of rice establishment and weed control
2002 2003 2002 2003 2002 2003 2002 2003 2002 2003
Cyhalofop/2,4-D/HW 73 73 159 159 119 119 193 193 136 136
Cyhalofop/chlorimuron+metsulfuron/HW 127 67 284 165 211 117 281 188 226 134
Pretilachlor/chlorimuron+metsulfuron/HW 177 74 306 183 230 119 292 196 251 143
Weed-free treatment 172 77 307 180 271 142 303 213 263 153
Weedy treatment 339 265 304 221 186 136 110 3 235 156
Mean 42 5 150 93 129 72 192 157
LSD (p ¼ 0.05)
For comparing two sub plot-means (W) at same main plot (T) 44.28 57.65
For two main plot (T) means comparison 27.09 51.19
For two subplot (W) means comparison 22.14 28.83
aCyhalofop/2,4-D/HW ¼ cyhalofop (at 120 g a.i. ha1 applied 14 DAS/DAT) followed by 2,4-D (at 500 g a.i. ha1 applied 21 DAS/DAT) followed by
hand-weeding at 35 DAS/DAT, cyhalofop/chlorimuron+metsulfuron/HW ¼ cyhalofop (at 120 g a.i. ha1 applied 14DAS/DAT) followed by
chlorimuron+metsulfuron (at 4 g a.i. ha1 applied 21DAS/DAT) followed by hand-weeding at 35DAS/DAT, pretilachlor/chlorimuron+metsulfuron/
HW ¼ pretilachlor with safener (at 500 g a.i. ha1 applied 3 DAS/DAT) followed by chlorimuron+metsulfuron (at 4 g a.i. ha1 applied 21DAS/DAT)
followed by hand-weeding at 35 DAS/DAT.
bADSB ¼ aerobic direct-seeded rice on furrow-irrigated raised-bed system (FIRBS); ADSR ¼ aerobic direct-seeded rice; ATPB ¼ aerobic transplanted
yield in ADSR with pretilachlor/chlorimuron+metsulfur-on/
HW and cyhalofop-butyl/chlorimuron+metsulfuron/
HW treatments did not differ and was significantly higher
than with the weedy check and cyhalofop-butyl/2,4-D/HW
treatment.
Net returns of ADSR and CPTR treatments (Table 7)
did not differ under weed-free situations, as direct sowing
resulted in substantial savings in production costs (Singh
et al., 2001). Among the herbicide treatments, pretilachlor/
chlorimuron+metsulfuron/HW treatment was superior in
attaining higher net returns that are similar to those of
weed-free situations under all methods of rice establish-ment.
The treatment with cyhalofop-butyl/2,4-D/HW gave
lower net income than with other herbicide combinations.
Cyhalofop-butyl/chlorimuron+metsulfuron/HW recorded
net returns comparable with those of pretilachlor/chlor-imuron+
metsulfuron/HW treatment. Thus, it can be
inferred that ADSR was as effective as CPTR in attaining
higher rice grain yield and net returns when weeds
were kept under control. Weed-free (six hand-weedings)
equivalent weed control could be obtained with pretila-chlor
with safener (at 500 g a.i. ha1 applied 3 DAS/DAT)
followed by chlorimuron+metsulfuron (at 4 g a.i. ha1
applied 21DAS/DAT) followed by hand-weeding at
35 DAS/DAT, irrespective of the method of rice establish-ment.
The next best treatment in attaining effective weed
control was cyhalofop-butyl (at 120 g a.i. ha1 applied
14 DAS/DAT) followed by chlorimuron+metsulfuron
(at 4 g a.i. ha1 applied 21 DAS/DAT) followed by hand-weeding
at 35 DAS/DAT. It is concluded that the ADSR
was as effective as conventionally puddle transplanted rice
in attaining higher rice grain yield and net returns when
weeds were kept under control using these identified
effective weed management treatments.
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