Efficacy and economics of different herbicides, their weed species selectivity, and the productivity of mechanized dry-seeded rice

Crop Protection 78 (2015) 239e246

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Efficacy and economics of different herbicides, their weed species selectivity, and the productivity of mechanized dry-seeded rice Tahir Hussain Awan a, b, *, Pompe C. Sta Cruz b, Bhagirath Singh Chauhan c ~ os, Philippines Weed Science, Crop and Environmental Sciences Division, International Rice Research Institute (IRRI), Los Ban ~ os, Philippines Crop Science Cluster, College of Agriculture, University of the Philippines Los Ban c Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Toowoomba 4350, Queensland, Australia a

b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 February 2015 Received in revised form 13 September 2015 Accepted 14 September 2015 Available online xxx

A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI) farm in ~ os, Philippines, to evaluate the economic performance of PRE oxadiazon and pendimethalin, early Los Ban POST butachlor plus propanil and thiobencarb plus 2,4-D, and late POST herbicides bispyribac-sodium and fenoxaprop plus ethoxysulfuron applied solely or sequentially. All herbicide treatments with PRE or early POST herbicides reduced total weed density by 85e100% and biomass by 80e100%, whereas late POST treatments reduced weed density by 32e50% and biomass by 40e62% compared with the nontreated weedy check. The highest grain yield was achieved in weed-free plots (5.9e6.1 t ha
1) and the lowest in weedy plots (0.2 t ha
1). Among the herbicide treatments, rice treated with oxadiazon, thiobencarb plus 2,4-D, and butachlor plus propanil followed by the late POST herbicides had grain yield increments of 23e25, 20 to 26, and 18 to 23 times that of the yield in weedy plots, respectively. The economic analysis showed that the sole application of oxadiazon provided the highest net profit and benefit-cost ratio in both years, which was similar to the treatments involving oxadiazon or early POST herbicides, followed by the sequential application of late POST herbicides. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Water and labour scarcity threaten the sustainability of the traditional rice production system in Asia. In South and Southeast Asia, the major rice establishment method is manual transplanting of seedlings into flooded soil. Flooded transplanted rice has the advantage of controlling the first cohorts of weeds because of standing water, which is known to suppress the germination of weeds that need oxygen to germinate. Furthermore, transplanted rice seedlings are larger than newly emerged weed seedlings, thus increasing the degree of competitive size asymmetry in the cropweed community and benefitting the crop at the expense of weeds (Weiner et al., 2001). The population in Asia is increasing at an alarming rate and more water is required for urbanization, whereas water resources are being depleted. Rice consumes about 50% of the total available irrigation water (Gianessi and Williams, 2011). The share of

* Corresponding author. Weed Science, Crop and Environmental Sciences Divi~ os, Philippines. sion, International Rice Research Institute (IRRI), Los Ban E-mail addresses: [email protected], [email protected] (T.H. Awan). http://dx.doi.org/10.1016/j.cropro.2015.09.016 0261-2194/© 2015 Elsevier Ltd. All rights reserved.

agriculture's water is declining because of competition with increased domestic and industrial uses (Kumar and Ladha, 2011). In the future, a noteworthy rice area will face water shortage and rice growers will not have enough water for rice cultivation on a large scale, particularly for puddling (land preparation in standing water is called puddling) and flood irrigation (Tuong and Bouman, 2003; Mahajan et al., 2012). In several Asian countries, increased economic growth has increased the labour demand for nonagricultural sectors and reduced the availability of labour for agriculture. Because of the increasing labour scarcity, labour wages have gone up, for example, in 1960, the wage was less than US$0.25 per day, but it has increased to $0.75, $1.25, $1.50, and $5.50 per day in Bangladesh, India, Sri Lanka, and the Philippines, respectively, making the traditional rice production system uneconomical in these countries (Gianessi and Williams, 2011; Kumar and Ladha, 2011). In Thailand and Malaysia, labour wages are $8.30 and $10.00 per day, respectively (Suria et al., 2011). Dry seeding of rice is one of the options to reduce the water and labour requirements for growing rice (Mahajan et al., 2011, 2012). Therefore, farmers in many Asian countries are shifting from puddled transplanted rice to dry-seeded

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rice. There are indications that mechanized dry-seeded rice will possibly increase in the future because it saves labour and time (Weerakoon et al., 2011; Chauhan, 2012). Dry-seeded rice systems require 35e57% less water and 67% less labour than transplanted rice (Mazid et al., 2003; Farooq et al., 2011). However, weeds are one of the most important biological constraints in dry-seeded rice systems (Subhas and Jitendra, 2001; Chauhan et al., 2012; Chauhan ~ a, 2012). and Open Dry-seeded rice systems are subject to much higher weed pressure than transplanted rice because of dry ploughing and aerobic soil conditions (Balasubramanian and Hill, 2002). Yield loss in dry-seeded rice due to weeds is 27e80% in Pakistan (Awan et al., 2006; Khaliq et al., 2012) and 40e70% in the Philippines (Phoung ~ a, 2013). Proper weed manageet al., 2005; Chauhan and Open ment is considered one of the most important prerequisites in dryseeded rice systems to ensure high crop yield. High weed pressure in dry-seeded rice lowers the economic returns and, in extreme cases, it causes complete failure of the rice crop (Jabran et al., 2012). Hence, judicious weed management in dry-seeded rice is a critical factor for securing and sustaining food security in Asia's developing countries (Timsina and Connor, 2001). Chemical weed management is the most popular method of weed control in rice because it is cheaper, more reliable, and more labour- and time-saving than other weed control measures (De Datta and Baltazar, 1996; Mazid et al., 2003). The use of herbicides in rice for controlling weeds has increased significantly over the last several years (FAO, 2002). This is because of increased labour wages, labour shortages, and a shift in rice planting method from transplanted to direct-seeded. For ecological weed management in dry-seeded rice, the use of herbicides is not ruled out, but they are used in combination with other weed management strategies. In Australia and Europe, herbicide use began with the introduction of direct-seeded rice (Bocchi et al., 2005; Taylor, 2007). In Asian countries, where direct seeding of rice is replacing transplanted rice, the use of herbicides has increased (Azmi et al., 2005; Rao et al., 2007; Weerakoon et al., 2011). Since dry-seeded rice has complex and diverse weed species, no single herbicide will control all weed species. Therefore, a combination of herbicides applied as a sequential application or in a mixture of two or more herbicides or a broad-spectrum herbicide along with other cultural practices is needed for effective control of sedges, broadleaves, and grasses. The use of herbicide mixtures is essential in response to changes in the weed community structure in dry-seeded rice (Sharma, 1997; Yaduraju and Mishra, 2004; Maity and Mukherjee, 2008). Several herbicides, with PRE activity, such as oxadiazon, oxadiargyl, butachlor, pendimethalin, thiobencarb, oxyfluorfen, and pyrazosulfuron, applied solely or with hand weeding, have been reported to provide effective control of weeds (Chauhan, 2012; ~ a, 2012; Mahajan and Chauhan, 2013). HowevChauhan and Open er, some issues related to the use of PRE herbicides exist, such as their limited window of application timing and an adequate soil moisture requirement at the time of their application (Singh et al., 2006). If optimum conditions are not available, POST herbicides may be a better option to manage weeds in dry-seeded rice systems (Singh et al., 2006; Mahajan and Chauhan, 2013). Previous research suggests that sequential applications of PRE and POST herbicides were very effective in controlling weeds in dry-seeded rice and they reduced weed density and biomass more than a single application of herbicides did (Singh et al., 2006; Chauhan et al., 2013; Mahajan and Chauhan, 2013; Ahmed and Chauhan, 2014). In another study, bispyribac-sodium was similar to manual weeding in controlling weeds and increasing rice yield (Khaliq et al., 2012), whereas others reported that this herbicide had little to no activity

on perennial sedges and grasses, such as Digera arvensis Forssk., Leptochloa chinensis, and Eragrostis spp. (Rao et al., 2007; Mahajan et al., 2009). In selecting herbicides or other weed control measures; there is also a need to consider the economics of weed control methods. In some situations, a weed control treatment may produce the highest yield but decrease the net return (Suria et al., 2011; Khaliq et al., 2012), making such a treatment impractical. However, such information is not available for the use of different PRE and POST herbicides in dry-seeded rice systems in the Philippines because mechanized dry-seeded rice is a newly emerging technology in this country. To provide wider options to farmers for economic weed control in dry-seeded rice, it is necessary to evaluate the efficacy and economics of different PRE and POST herbicides when used solely and sequentially. Therefore, a study was designed to evaluate the efficacy and economics of different PRE and POST herbicides used alone or sequentially.

2. Materials and methods 2.1. Experimental site The experiments were conducted at the International Rice ~ os (14.13 N, 121.13 E), Research Institute (IRRI) farm, Los Ban Philippines, to evaluate the efficacy and economics of different weed control programs in dry-seeded rice.

2.2. Study material NSICRC 82 (IR154), a short-duration (110 d) variety, was planted. Nine herbicides were evaluated for weed control and economics. Two PRE herbicides, oxadiazon (Ronstar, Bayer Crop Science) and pendimethalin (Herbadox, Cyanamid); four early POST herbicides, butachlor plus propanil (Advance, Monsanto Philippines Inc.) and thiobencarb plus 2,4-D (Grassedge, Biostadt Philippines Inc.); and three late POST herbicides, bispyribac-sodium (Nominee, Bayer Crop Science) and fenoxaprop plus ethoxysulfuron (Rice Star Xtra, Bayer Crop Science), were included. The experimental area was cultivated with two diskings, followed by two passes of a rotovator (a machine with rotating blades for breaking up or tilling the soil). Rice was sown on May 7, 2012, and harvested on September 8, 2012; in 2013, the crop was planted on January 22 and harvested on May 9. Rice at 50 kg ha
1 was sown with a tractor-mounted seed drill at a 20-cm row spacing and a depth of 1e2 cm. The plot size was 3.6 m by 6.0 m. Immediately after sowing, the field was surface-irrigated. Phosphorus (P) and potash (K) fertilizers were applied as basal fertilizer in the form of solophos (20% P2O5) and muriate of potash (60% K2O) at 40 and 40 kg ha
1, respectively. Crop emergence started at 3 d after sowing (DAS) and was completed at 10 DAS. After crop emergence, nitrogen (N) was applied as urea at 150 kg ha
1 in three splits, such as 30, 30, and 40% at 15, 35, and 60 DAS, respectively. Herbicides were applied with a knapsack sprayer calibrated to deliver 220 L ha
1 of spray solution through flat-fan nozzles at a spray pressure of 140 kPa. Oxadiazon at 500 g ai ha
1 and pendimethalin at 1000 g ai ha
1 were applied at 2 DAS. The schedule and dose of all other herbicides and their combinations are shown in Table 1. Thirteen treatments were arranged in a randomized complete block design with three replications. In the weed-free treatment, three hand weedings were done at 14, 34, and 59 DAS. These timings corresponded to 1 d prior to N fertilization. An non-treated plot was added for comparison.

T.H. Awan et al. / Crop Protection 78 (2015) 239e246

241

Table 1 Herbicide dose and timing of application.a Weed control treatment

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Weed-free Non-treated (weedy) a

Herbicide dose

Application timing

g ai ha
1

Days after sowing

30 30 fb 30 600 fb 45 45 500 500 fb 30 500 fb 45 1000 1000 fb 30 1000 fb 45 800 fb 45 e e

14 14 fb 22 5 fb 22 22 2 2 fb 14 2 fb 22 2 2 fb 14 2 fb 22 5 fb 22 e e

Abbreviations: DAS ¼ days after sowing; fb ¼ followed by.

2.3. Observations and measurements Rice plant densities were determined from four rows by randomly placing a 1-m-long stick in each plot at 14 DAS. Weed density and biomass were measured at 40 DAS. Weed density was determined from two 40 by 40-cm quadrats placed randomly in each plot. Weeds were uprooted, washed with tap water, sun-dried, counted species-wise, and separately oven-dried at 70  C for constant dry weight, and then weighed. At crop maturity, rice was harvested from an area of 4.8 m2 from the yield area. Grain yield and moisture were recorded. Grain yield was expressed in t ha
1 at 14% moisture content. 2.4. Statistical analyses Data were analysed using analysis of variance (ANOVA). ANOVA results showed an interaction between year and treatments; therefore, the data were analysed separately using STAR 3.0 V (IRRI, Philippines). Treatment means were separated using the least significant difference (LSD) at the 5% level of significance. Weed density and biomass data were subjected to square-root transformation [√(x plus 0.5)] before analyses. The transformation, however, did not improve the results, so nontransformed data were used. Differences were considered significant only at P  0.05. The relationships between rice grain yield and weed biomass were assessed with the use of correlation analysis (SigmaPlot 10.0). 3. Results and discussion 3.1. Composition of weed flora The study was conducted under a naturally occurring population of mixed weeds, dominated by grass and broadleaf weeds. There were 21 different weed species at the experimental site. Even though several weed species were present at the site, the dominant weeds were three grass species: Echinochloa colona (L.) Link, L. chinensis (L.) Nees, and Echinochloa crus-galli (L.) Beauv.; two broadleaf species: Eclipta prostrata (L.) L. and Ludwigia hyssopifolia (G. Don) Exell; and two sedge species: Cyperus iria L. and Fimbristylis miliacea (L.) Vahl. 3.2. Weed density and biomass at 40 days after sowing 3.2.1. L. chinensis PRE oxadiazon and pendimethalin and early POST butachlor plus propanil and thiobencarb plus 2,4-D herbicides reduced the

weed density of L. chinensis by 96e100% and the biomass by 85e100% compared with the nonntreated weedy check in 2012. In an earlier study, pendimethalin PRE alone reduced the biomass of this weed by 94% and the sequential application of pendimethalin PRE and azimsulfuron POST reduced L. chinensis and large crabgrass (Digitaria sanguinalis (L.) Scop. DIGSA] biomass by more than 96% (Mahajan and Chauhan, 2013). In this study, a high weed density was recorded for the bispyribac-sodium-treated plots (813 plants m
2) followed by the fenoxaprop plus ethoxysulfuron-treated plots (476 plants m
2) and weedy plots (584 plants m
2) (Table 2). The corresponding values for weed biomass in these treatments were 140, 66, and 53 g m
2, respectively (Table 3). A similar trend for weed density and biomass was observed in 2013 (Tables 4 and 5). It is evident from the results that bispyribac-sodium did not control L. chinensis. Compared to the nontreated weedy plots, the sole application of fenoxaprop plus ethoxysulfuron showed little efficacy against this weed. It reduced weed density by only 19 and 20% and weed biomass by 24 and 13% in 2012 (Tables 2 and 3) and 2013 (Tables 4 and 5), respectively. Results of this study are in line with earlier findings that a single application of bispyribac-sodium at the six- and eight-leaf stages provided 1 and 0% control of L. chinensis, respectively (Chauhan and Abugho, 2012).

3.2.2. E. colona E. colona treated with all herbicide combinations, except for fenoxaprop plus ethoxysulfuron, resulted in a reduced density of 82e100% in 2012 (Table 2). A similar trend of reducing weed density by 94e100% was observed in 2013 (Table 4). During both experiments, the sole application of fenoxaprop plus ethoxysulfuron did not provide effective control of E. colona and reduced its density by only 20% in 2012 (Table 2) and by 40% in 2013 (Table 4) compared to the weedy control. Similar to weed density, all herbicide treatments, except for the sole application of fenoxaprop plus ethoxysulfuron, reduced E. colona biomass by 54e100% in the first experiment (Table 3) and by 84e100% in the second experiment (Table 5). Similar results were reported in an earlier study, in which, compared with the nontreated check, E. colona density declined by more than 99% with the sequential application of pendimethalin PRE followed by bispyribac-sodium late POST (Mahajan and Chauhan, 2013). Our results are also in line with a recent study in which oxadiargyl and pendimethalin reduced E. colona density to 8.3 and 4.2 plants m
2 and biomass to 0.3 and 0.1 g m
2, respectively, compared with the control (Ahmed and Chauhan, 2014).

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T.H. Awan et al. / Crop Protection 78 (2015) 239e246

Table 2 Effect of herbicide treatment on weed density (number m
2) at 40 d after sowing in 2012.a Weed control treatment

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Non-treated (weedy) LSD0.05 a

Herbicide dose

Application timing

Weed density

g ai ha
1

DAS

No. m
2

30 30 fb 30 600 fb 45

14 14 fb 22 5 fb 22

45 500 500 fb 30 500 fb 45

Echinochloa colona

Echinochloa crus-galli

645.8 812.5 0.0

2.1 10.4 10.4

1.0 0.0 0.0

0.0 8.3 3.1

22 2 2 fb 14 2 fb 22

476.0 3.1 3.1 2.1

61.5 3.1 0.0 9.4

0.0 0.0 0.0 0.0

1000 1000 fb 30 1000 fb 45

2 2 fb 14 2 fb 22

1.0 6.3 21.9

1.0 7.3 2.1

800 fb 45

5 fb 22

1.0 584.4 345.2

e e

Leptochloa chinensis

Cyperus iria

Fimbristylis miliacea

Ludwigia hyssopifolia

Eclipta prostrata

Total

0.0 0.0 0.0

0.0 0.0 0.0

0.0 1.0 0.0

648.9 832.2 13.5

343.8 11.5 0.0 1.0

149.0 0.0 0.0 1.0

6.3 0.0 0.0 2.1

1.0 0.0 0.0 1.0

1037.5 17.7 3.1 16.6

0.0 0.0 2.1

159.4 36.5 75.0

0.0 1.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

161.5 51.0 101.0

13.5

0.0

180.2

0.0

0.0

1.0

195.7

77.1 34.5

5.0 NS

425.0 377.9

14.6 3.0

2.1 NS

1.1 NS

1109.3 375.9

Abbreviations: DAS ¼ days after sowing; fb ¼ followed by; LSD0.05 ¼ least significant difference at 5% level of significance; NS ¼ nonsignificant.

density by only 63% compared to the nontreated control. Our results are in line with earlier findings, in which pendimethalin provided low control of sedges (Ahmed and Chauhan, 2014). Bispyribac-sodium as POST reduced C. iria density by 98% and fenoxaprop plus ethoxysulfuron reduced its density by only 19% (Table 2). A similar trend was found in 2013 (Table 4). Similar results were reported in an earlier study, in which pendimethalin PRE followed by bispyribac-sodium POST reduced C. iria density by 99% compared with that of the nontreated control (Mahajan and Chauhan, 2013). Similar to C. iria density, maximum biomass of 228.6 g m
2 was recorded in the control plots, which, in the herbicide-treated plots, declined to 0e80 g m
2. In 2012, among the herbicide-treated plots, maximum biomass was recorded in the sole fenoxaprop plus ethoxysulfuron (80 g m
2) and sole pendimethalin (57.5 g m
2) treatments. Minimum C. iria biomass of 0e2.7 g m
2 was recorded in the plots applied with oxadiazon, bispyribac-

3.2.3. E. crus-galli In 2012, compared to the nontreated weedy plots, all herbicide treatments, except those involving pendimethalin with fenoxaprop plus ethoxysulfuron and sole bispyribac-sodium application, reduced E. crus-galli density and biomass by 100% (Tables 2 and 3). A similar trend was found in the 2013 experiment (Tables 4 and 5). 3.2.4. C. iria For 2012, the maximum weed density (425 plants m
2) was recorded in the weedy plots, which was similar to the density (344 plants m
2) in the plots treated with fenoxaprop plus ethoxysulfuron alone (Table 2). Compared to the nontreated weedy plots, all herbicide treatments, except fenoxaprop plus ethoxysulfuron sole (19%), sole pendimethalin (63%), and thiobencarb plus 2,4-D followed by late POST (58%), reduced C. iria density by 80e100%. Among the PRE herbicides, the sole application of oxadiazon reduced C. iria density by 97% and sole pendimethalin reduced its

Table 3 Effect of herbicide treatment on weed biomass (g m
2) at 40 d after sowing in 2012.a Weed control treatment

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Non-treated (weedy) LSD0.05 a

Herbicide dose

Application timing

Weed biomass

g ai ha
1

DAS

g m
2

30 30 fb 30 600 fb 45

14 14 fb 22 5 fb 22

45 500 500 fb 30 500 fb 45

Echinochloa colona

Echinochloa crus-galli

117.5 140.4 0.0

1.3 5.4 14.1

1.0 0.0 0.0

22 2 2 fb 14 2 fb 22

65.6 2.8 1.8 5.0

31.7 4.9 0.0 16.5

1000 1000 fb 30 1000 fb 45

2 2 fb 14 2 fb 22

4.6 4.0 8.0

800 fb 45

5 fb 22 e e

Leptochloa chinensis

Cyperus iria

Fimbristylis miliacea

Ludwigia hyssopifolia

Eclipta prostrata

Total

1.4 0.0 1.5

0.0 0.0 0.0

0.0 0.0 0.0

0.0 0.2 0.0

121.2 146.0 15.6

0.0 0.0 0.0 0.0

79.5 2.7 0.0 0.2

7.8 0.0 0.0 0.0

0.0 0.0 0.0 0.2

0.1 0.0 0.0 0.0

184.7 10.4 1.9 21.9

0.4 10.9 13.9

0.0 0.0 1.8

57.5 13.9 28.7

0.0 0.1 0.0

0.0 0.0 0.0

0.0 0.0 0.0

62.5 28.9 52.3

0.0

3.0

0.0

45.3

0.0

0.0

0.4

48.8

52.8 46.6

30.1 7.8

1.2 NS

228.6 57.6

1.6 NS

0.2 NS

0.3 NS

315.0 74.9

Abbreviations: DAS ¼ days after sowing; fb ¼ followed by; LSD0.05 ¼ least significant difference at 5% level of significance; NS ¼ nonsignificant.

T.H. Awan et al. / Crop Protection 78 (2015) 239e246

243

Table 4 Effect of herbicide treatments on weed density (number m
2) at 40 d after sowing in 2013.a Weed control treatment

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Non-treated (weedy) LSD0.05 a

Herbicide dose

Application timing

Weed density

g ai ha
1

DAS

No. m
2

30 30 fb 30 600 fb 45

14 14 fb 22 5 fb 22

21.9 12.5 0.0

31.3 0.0 0.0

4.2 0.0 0.0

1.0 0.0 0.0

45 500 500 fb 30 500 fb 45

22 2 2 fb 14 2 fb 22

37.5 0.0 0.0 0.0

35.4 2.1 0.0 0.0

9.4 1.0 1.0 0.0

1000 1000 fb 30 1000 fb 45

2 2 fb 14 2 fb 22

0.0 0.0 0.0

3.1 0.0 0.0

800 fb 45

5 fb 22

0.0 46.9 30.9

Leptochloa chinensis

Echinochloa colona

Echinochloa crus-galli

Cyperus iria

Fimbristylis miliacea

Ludwigia hyssopifolia

Eclipta prostrata

Total

0.0 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

58.4 12.5 0.0

50.0 0.0 0.0 0.0

2.1 0.0 0.0 0.0

0.0 0.0 0.0 0.0

1.0 0.0 0.0 0.0

135.4 3.1 1.0 0.0

1.0 0.0 0.0

84.4 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

88.5 0.0 0.0

1.0

2.1

0.0

0.0

0.0

0.0

3.1

59.4 31.6

57.3 16.6

403.1 77.2

16.7 2.2

1.1 NS

3.1 NS

587.6 131.9

Abbreviations: DAS ¼ days after sowing; fb ¼ followed by; LSD0.05 ¼ least significant difference at 5% level of significance; NS ¼ nonsignificant.

non-treated control (Tables 2e5). Results exhibited and proved that all tested herbicides were very effective in controlling this weed in the dry-seeded rice system.

sodium, and butachlor plus propanil in combinations with other herbicides (Table 3). In 2013, all herbicides reduced C. iria biomass by 100%, except for the sole fenoxaprop plus ethoxysulfuron (63%) and sole pendimethalin (83%) treatments (Table 5). In an earlier study, researchers found that pendimethalin PRE followed by bispyribac-sodium POST reduced C. iria biomass more than other herbicide treatments (Mahajan and Chauhan, 2013). The single application of bispyribac-sodium POST provided similar C. iria biomass reduction to the application of pendimethalin PRE followed by penoxsulam or azimsulfuron POST or pyrazosulfuron PRE followed by bispyribac-sodium or azimsulfuron POST (Mahajan and Chauhan, 2013).

3.3. Total weed density and biomass at 40 days after sowing All herbicide treatments reduced total weed density and biomass compared with the non-treated check. In 2012, all herbicide combinations which had PRE or early-POST herbicides reduced total weed density by 85e99% (Table 2) and biomass by 80e99% (Table 3). The sole application of oxadiazon and pendimethalin reduced weed density by 99.7% and 96.1% and biomass by 96.7% and 87.1%, respectively. This suggested that a single application of these PRE herbicides under optimum conditions is enough to reduce weed density and biomass considerably. On the other hand, sole bispyribac-sodium, bispyribac-sodium followed by bispyribacsodium, and sole fenoxaprop plus ethoxysulfuron (all late-POST

3.2.5. F. miliacea In both years, all herbicide treatments, except the sole application of fenoxaprop plus ethoxysulfuron, reduced F. miliacea density by 99e100% and biomass by 95e100% compared with that of the

Table 5 Effect of herbicide treatments on weed biomass (g m
2) at 40 d after sowing in 2013.a Weed control treatment

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Non-treated (weedy) LSD0.05 a

Herbicide dose

Application timing

Weed biomass

g ai ha
1

DAS

g m
2

30 30 fb 30 600 fb 45

14 14 fb 22 5 fb 22

0.6 0.2 0.0

1.8 0.0 0.0

0.3 0.0 0.0

45 500 500 fb 30 500 fb 45

22 2 2 fb 14 2 fb 22

0.0 0.0 0.0 0.0

0.6 0.6 0.0 0.0

1000 1000 fb 30 1000 fb 45

2 2 fb 14 2 fb 22

0.0 0.0 0.0

800 fb 45

5 fb 22

Leptochloa chinensis

Echinochloa colona

Echinochloa crus-galli

Cyperus iria

Fimbristylis miliacea

Ludwigia hyssopifolia

Eclipta prostrata

0.0 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

2.7 0.2 0.0

0.1 1.6 0.0 0.0

11.6 0.0 0.0 0.0

0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0

12.5 2.2 0.0 0.2

2.5 0.0 0.0

0.4 0.0 0.0

5.5 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

0.0 0.0 0.0

8.4 0.0 0.0

0.0

0.6

1.4

0.0

0.0

0.0

0.0

2.0

1.5 NS

20.9 7.9

14.3 6.0

31.7 8.4

0.2 0.9

0.0 NS

0.1 NS

68.7 17.2

Abbreviations: DAS ¼ days after sowing; fb ¼ followed by; LSD0.05 ¼ least significant difference at 5% level of significance; NS ¼ nonsignificant.

Total

244

T.H. Awan et al. / Crop Protection 78 (2015) 239e246

herbicides) reduced weed density by only 26, 41, and 7% and weed biomass by 62, 54, and 40%, respectively, compared to the nontreated control (Tables 2 and 3). A similar trend of declining weed density (85e100%) and biomass (82e100%) was observed in 2013 (Tables 6 and 7). Results are consistent with an earlier study conducted in Sri Lanka, in which pendimethalin and oxadiazon used as PRE herbicides controlled total weed density by 85e87%, and the plots treated with these PRE herbicides followed by the application of fenoxaprop plus ethoxysulfuron controlled the weeds by 95e98% (Chauhan et al., 2013). In another study, Anwar et al. (2013) found that PRE application of pretilachlor reduced weed biomass by 70% and weed density by 69% and different early-POST herbicides reduced weed density by 39e90% and biomass by 40e90%, compared to the non-treated weedy plots. The results of the current study suggested that both PRE and late-POST herbicides, if used properly, were effective in suppressing weeds in dry-seeded rice. Results showed that a single application of bispyribacsodium was not effective enough to reduce weed density and biomass compared with a double application of it. Similar results were found in an earlier study in Malaysia (Anwar et al., 2013). Oxadiazon and pendimethalin are commonly used as PRE herbicides to control a broad spectrum of weeds in dry-seeded rice ~ a, 2012; Chauhan systems (Singh et al., 2007; Chauhan and Open et al., 2013). In the present study also, these herbicides were effective in controlling weeds. In general, an additional spray of late-POST herbicides had no significant effect compared with the effect of PRE herbicides. Such results could be explained in two ways: PRE herbicides were quite effective or late-POST herbicide application did not control some of the problematic weeds. 3.4. Correlation between weed biomass and rice grain yield A negative linear regression was found between grain yield and weed biomass at 40 DAS in 2012 (y ¼ 4.96e0.02x) and 2013 (y ¼ 5.43e0.10x). The relationship was slightly stronger in 2012 (R2 ¼ 0.82) than in 2013 (R2 ¼ 0.72). Similar results were reported for other herbicides in previous studies in Bangladesh (Ahmed and Chauhan, 2014), in India (Mahajan and Chauhan 2013), and in the

~ a, 2013), in which researchers found Philippines (Chauhan and Open that grain yield was negatively correlated with weed biomass at different stages of growth. 3.5. Grain yield Among all the treatments, the highest grain yield (5.9e6.1 t ha
1) was achieved in the weed-free plots. Different herbicide treatments strongly influenced weed control and grain yield. All herbicide, except for fenoxaprop plus ethoxysulfuron, provided 440e2440% and 1380e2570% higher grain yield than the non-treated control in 2012 and 2013, respectively (Table 6). Results showed that, among all herbicide treatments, the plots treated solely with oxadiazon produced the highest yield (5.6 t ha
1) in 2012. In 2013, sole oxadiazon and oxadiazon followed by late-POST herbicides produced the highest yield (5.4e5.8 t ha
1), which was similar to early-POST followed by late-POST herbicides (4.5e5.9 t ha
1). Among all treatments, the lowest paddy yield was produced in the plots treated solely with bispyribac-sodium (2.0e3.4 t ha
1) and fenoxaprop plus ethoxysulfuron (0.6e4.3 t ha
1) (Table 6). The sole application of oxadiazon increased yield by 77.7 and 36.4% over that with sole pendimethalin in 2012 and 2013, respectively. These results are in line with earlier findings in which the highest grain yield was recorded in the plots treated with oxadiargyl followed by ethoxysulfuron (4.1 t ha
1) and pendimethalin followed by ethoxysulfuron (4.1 t ha
1) (Ahmed and Chauhan, 2014). The lowest yield was obtained from the plots treated with bispyribac-sodium alone as compared with others treated with PRE followed by POST herbicides (Anwar et al., 2013) Results showed that plots treated with bispyribac-sodium produced a much lower yield in 2012 (1.2e2.0 t ha
1) than in 2013 (3.4e5.4 t ha
1) (Table 6). This difference in yield may be due to the higher density of L. chinensis in 2012 than in 2013 (Tables 2 and 3), which was not controlled by bispyribac-sodium and became the cause of the yield reduction. Our results proved that bispyribacsodium had no efficacy (0% control) on L. chinensis. Similar results were reported in an earlier study in dry-seeded rice, in which bispyribac-sodium was weak against some perennial sedges and grasses, such as L. chinensis and Eragrostis spp. (Mahajan et al., 2009).

Table 6 Effect of herbicide treatments on grain yield and percent yield increase compared with the non-treated treatments in 2012 and 2013.a Weed control treatment

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Weed-free Non-treated (weedy) LSD0.05

Herbicide dose

Application timing

2012 Grain yield

Yield increase over non-treated weedy

2013 Grain yield

Yield increase over non-treated weedy

g ai ha
1 30 30 fb 30 600 fb 45

DAS 14 14 fb 22 5 fb 22

t ha
1 2.0 1.2 4.1

% 800 440 1770

t ha
1 3.4 5.4 5.4

% 1380 2240 2230

45 500 500 fb 30 500 fb 45

22 2 2 fb 14 2 fb 22

0.6 5.6 5.1 5.2

190 2440 2200 2260

4.3 5.4 5.2 5.8

1760 2230 2160 2440

1000 1000 fb 30 1000 fb 45

2 2 fb 14 2 fb 22

3.1 3.8 4.1

1330 1620 1770

3.9 5.6 4.9

1610 2320 2040

800 fb 45

5 fb 22

4.5

1920

6.0

2570

5.9 0.2 2.0

2600 e

6.1 0.2 1.2

2500 e

a Abbreviations: DAS ¼ days after sowing; fb ¼ followed by; LSD0.05 ¼ least significant difference at 5% level of significance; NS ¼ nonsignificant. Grain yield data was used in a previous paper (Awan et al., 2015).

Pesos (P) is the Philippine currency. US$1 ¼ P44.50. Manual weeding cost ¼ 100 per labourer for first weeding plus 50 for second weeding plus 25 for third weeding. Labour cost at P250 labourer
1 d
1. Market price of herbicides as oxadiazon ¼ P820 L
1, pendimethalin ¼ P550 L
1, butachlor plus propanil ¼ P630 L
1, thiobencarb plus 2,4-D IBE ¼ P625 L
1, fenoxaprop plus ethoxysulfuron ¼ P2260 L
1 and bispyribacesodium ¼ P5920 L
1. Market price of paddy ¼ P20,000 t
1. Gross income ¼ (paddy yield  market paddy price t
1). Net benefit ¼ (gross income e total cost). Benefit-cost ratio ¼ Benefit/cost. a Abbreviations: fb ¼ followed by; LSD0.05 ¼ least significant difference at 5% level of significance; NS ¼ nonsignificant.

0.3
0.9 650
1020 1124 674 561.8 þ 280.9 þ 140.5 0.0 0 0

2107 674

5.9 0.2

2670 100

565
1025

0.3
0.9

6.1 0.2

2755 105

1.3 1520 674 6.7 14.1 þ 25.4

720

4.5

2000

830

0.7

6.0

2690

0.5 1.1 0.9 600 1305 1020 1124 1124 1124 6.7 6.7 6.7 37.1 37.1 þ 33.3 37.1 þ 25.4

1167 1201 1193

3.1 3.8 4.1

1410 1700 1850

245 500 660

0.2 0.4 0.6

3.9 5.6 4.9

1765 2505 2210

0.7 1.1 0.9 1.2 765 1240 1130 1430
0.4 1.2 0.9 1.0 1124 1124 1124 1124 6.7 6.7 6.7 6.7 25.4 36.9 36.9 þ 33.3 36.9 þ 25.4

1156 1167 1201 1193

1.6 5.6 5.1 5.2

735 2510 2275 2335


420 1340 1075 1145

4.3 5.4 5.2 5.8

1920 2410 2335 2620

0.3 1.0 1.0 365 1220 1225 1530 2420 2405 3.4 5.4 5.4
0.3
0.6 0.6
274
667 670

2013 2012

890 530 1850 2.0 1.2 4.1 1164 1197 1181 1124 1124 1124 6.7 6.7 6.7 33.3 33.3 þ 33.3 24.8 þ 25.4

Bispyribac-sodium Bispyribac-sodium fb bispyribac-sodium Butachlor plus propanil fb fenoxaprop plus ethoxysulfuron Fenoxaprop plus ethoxysulfuron Oxadiazon Oxadiazon fb bispyribac-sodium Oxadiazon fb fenoxaprop plus ethoxysulfuron Pendimethalin Pendimethalin fb bispyribac-sodium Pendimethalin fb fenoxaprop plus ethoxysulfuron Thiobencarb plus 2,4-D fb fenoxaprop plus ethoxysulfuron Weed-free Non-treated (weedy)

Herbicides/manual weeding (1)

Cost of production (US$ ha
1) Weed control treatment

Table 7 Economics of different weed control treatments and their effect on cost of production, net benefit, and benefit-cost ratio for 2012 and 2013.a

Gross income Net benefit Benefit-cost Yield Gross income Net benefit Benefit-cost Spray Other common Total Yield ($ ha
1) ratio (t ha
1) ($ ha
1) ($ ha
1) ratio application (2) production (3) (4 ¼ 1 þ 2þ3) (t ha
1) ($ ha
1)

T.H. Awan et al. / Crop Protection 78 (2015) 239e246

245

Yield was higher in the plots treated with PRE or early-POST herbicides followed by late-POST herbicides than in those treated with late-POST herbicides alone. Because PRE or early-POST herbicides provided excellent control of grass, sedge, and broadleaf weeds in the early growth season, rice experienced very little competition with weeds and started a good growth, which helped in early canopy closure and in suppressing later-germinating weeds. These late-germinating weeds can be easily controlled through the application of late-POST herbicides. The findings of the current study were supported by an earlier study in which the plots that received PRE herbicides followed by one-time hand weeding caused faster canopy closure, which suppressed weed growth at later stages (Ahmed and Chauhan, 2014). 3.6. Economic analysis The effectiveness of any production system is ultimately evaluated on the basis of its economics (Table 7). Economic analysis revealed that the highest net benefit (US$1340 ha
1) and benefitcost ratio (1.2 in 2012) were achieved from the plots treated with oxadiazon alone, which were similar to the sequential application of oxadiazon and late-POST herbicides, having net benefits of US$1075 to 1145 ha
1 and benefit-cost ratios of 0.9e1.0. In 2013, thiobencarb plus 2,4-D with sequential application of fenoxaprop plus ethoxysulfuron herbicide provided the highest net benefit of US$1520 ha
1, which was similar to that of the sequential application of oxadiazon with late-POST herbicides (US$1430 ha
1). Although the highest grain yield (5.9e6.1 t ha
1) was produced in weed-free plots, the net benefit (US$565 to 650 ha
1) was lower when compared with all herbicide-treated plots, except for those with sole application of bispyribac-sodium and fenoxaprop plus ethoxysulfuron, because of higher labour costs involved in hand weeding. Economic analysis revealed that, when weeds were not controlled, farmers had to face a loss of US$1025 ha
1 and the benefit:cost ratio was negative (
0.9). Furthermore, in 2012, results showed that, when herbicide selection (e.g., bispyribac-sodium) was not right according to the weed species (e.g., L. chinensis) present in the field, instead of earning profit, farmers had to bear a loss of US$274 to 667 ha
1 (Tables 2 and 7). On the other hand, the same herbicide (e.g., bispyribac-sodium) provided a profit of US$365 to 1220 ha
1 when the site was not much infested by L. chinensis (Tables 4 and 7). Our findings of the cost-effectiveness of herbicides for weed management in dry-seeded rice are in line with previous studies, in which researchers found that weed control with appropriate herbicides provided higher net benefits than manual hand weeding (Hasanuzzaman et al., 2008; Suria et al., 2011; Khaliq et al., 2012). In summary, the highest net benefit can be achieved by using oxadiazon as a PRE or thiobencarb plus 2,4-D and butachlor plus propanil as early-POST herbicides. PRE herbicides can control annual grasses, sedges, and broadleaf weed species because of their residual activity in the soil. In this regard, oxadiazon PRE should be used once rice seeds have imbibed water, but prior to the emergence of rice and weeds. The application of PRE herbicides requires optimum conditions for their application. If any rice grower, because of the limitations of such conditions, is unable to apply PRE herbicides, the application of early-POST herbicides can also provide maximum benefit. If there is a second cohort of weeds, use the sequential application of an appropriate POST herbicide according to the weed species present in the field. Our study concluded that the use of herbicides is an efficient and cost-effective method for weed control in dry-seeded rice. Hand weeding can be adopted in those areas where labour is easily available and inexpensive. When the herbicide selection is right, treatments comprising only

246

T.H. Awan et al. / Crop Protection 78 (2015) 239e246

herbicides require less cost but produce higher net benefits than manual weeding. On the contrary, when the herbicide selection is not right according to the weed species, it would produce the lowest net benefit and, sometimes, an economic loss instead of a net profit. Our study suggests that various herbicide options are available to control weeds economically in dry-seeded rice systems. Mechanized dry-seeded rice is a new system in Asia, including in the Philippines, and the availability of economic analysis of different herbicide options will help in promoting this system. Before dryseeded rice systems spread widely across Asia, there is a need to develop integrated weed management strategies involving the use of a stale seedbed, narrow row spacing, high seeding rates, weedcompetitive cultivars, and economical herbicide combinations for the effective control of grass, sedge, and broadleaf weeds. Acknowledgements Authors would like to thanks Bill Hardy for providing comments on the manuscript. References Ahmed, S., Chauhan, B.S., 2014. Performance of different herbicides in dry-seeded rice in Bangladesh. Sci. World J. http://dx.doi.org/10.1155/2013/729418. Anwar, M.P., Juraimi, A.S., Mohamed, M.T.M., Uddin, M.K., Samedani, B., Puteh, A., Man, A., 2013. Integration of agronomic practices with herbicides for sustainable weed management in aerobic rice. Sci. World J. http://dx.doi.org/10.1155/ 2013/916408. Awan, T.H., Sta Cruz, P.C., Chauhan, B.S., 2015. Agronomic indices, growth, yieldcontributing traits, and yield of dry-seeded rice under varying herbicides. Field Crops Res. 177, 15e25. Awan, T.H., Safdar, M.E., Manzoor, Z., Ashraf, M.M., 2006. Screening of herbicides as posteemergence application for effective weed control without affecting growth and yield of direct seeded rice plant. J. Anim. Plant Sci. 16, 60e65. Azmi, M., Chin, D.V., Vongsaroj, P., Johnson, D.E., 2005. Emerging issues in weed management of direct-seeded rice in Malaysia, Vietnam, and Thailand. In: Toriyama, K., Heong, K.L., Hardy, B. (Eds.), Rice Is Life: Scientific Perspectives for ~ os, Philippines, the 21st Century. International Rice Research Institute, Los Ban and Japan International Research Center for Agricultural Sciences, Tsukuba, Japan, pp. 196e198. Balasubramanian, V., Hill, J.E., 2002. Direct seeding of rice in Asia: emerging issues and strategic research needs for the 21st century. In: Pandey, S., Velasco, L. (Eds.), Direct Seeding: Research Strategies and Opportunities. International Rice ~ os, Philippines, pp. 15e39. Research Institute, Los Ban Bocchi, S., Callegarin, A.M., Baldi, G., 2005. Rice production system in Italy and its sustainability. In: Productio'n arroz en Italia, Asociacio'n Cultivadores de Arroz, Italy, p. 39. Chauhan, B.S., 2012. Weed ecology and weed management strategies for dryseeded rice in Asia. Weed Technol. 26, 1e13. Chauhan, B.S., Abugho, S.B., 2012. Effect of growth stage on the efficacy of postemergence herbicides on four weed species of direct-seeded rice. Sci. World J. 7. Article ID 123071. Chauhan, B.S., Anuruddika, S.K., Abeysekara, Sakinda, D., Kulatunga, Upali, B., Wickrama, 2013. Performance of different herbicides in a dry-seeded rice system in Sri Lanka. Weed Technol. 27, 459e462. Chauhan, B.S., Mahajan, G., Sardana, V., Timsina, J., Jat, M.L., 2012. Productivity and sustainability of the rice-wheat cropping system in the Indo-Gangetic Plains of the Indian subcontinent: problems, opportunities, and strategies. Adv. Agron. 117, 315e369. ~ a, J., 2012. Effect of tillage systems and herbicides on weed Chauhan, B.S., Open emergence, weed growth, and grain yield in dry-seeded rice systems. Field Crops Res. 137, 56e69. ~ a, J., 2013. Weed management and grain yield of rice sown at Chauhan, B.S., Open low seeding rates in mechanized dry-seeded systems. Field Crops Res. 141, 9e15. De Datta, S.K., Baltazar, A., 1996. Weed control technology as a component of rice production systems. In: Auld, B., Kim, K.U. (Eds.), Weed Management in Rice, pp. 25e52. FAO Plant Production and Protection Paper, No. 139.

FAO, 2002. Major weed problems in rice e red/weedy rice and the Echinochloa complex e R. Labrada. In: Rice Information Volume 3. Food and Agriculture Organization of the United Nations, Rome. http://www.fao.org/docrep/005/ y4347e/y4347e03.htm#bm03. accessed 09.05.14. Farooq, M., Kadambot, H.M., Siddique, Rehman, H., Aziz, T., Lee, D.J., Wahid, A., 2011. Rice direct seeding: experiences, challenges and opportunities. Soil Tillage Res. 111, 87e98. Gianessi, L., Williams, A., 2011. Herbicides Are Key for the Sustainability of Rice Growing in South Asia. International Pesticide Benefits Case Study No. 7. http:// croplifefoundation.files.wordpress.com/2012/07/7ericeeherbicide.pdf. Hasanuzzaman, M., Islam, M.O., Bapari, M.S., 2008. Efficacy of different herbicides over manual weeding in controlling weeds in transplanted rice. Aust. J. Crop Sci. 2, 18e24. Jabran, K., Farooq, M., Hussain, M., 2012. Efficient weed control with penoxsulam application ensures higher productivity and economic return of direct seeded rice. Int. J. Agric. Biol. 14, 901e907. Khaliq, A., Matloob, A., Ahmed, N., Rasul, F., Awan, I.U., 2012. Late POST emergence chemical weed control in direct seeded fine rice. J. Anim. Plant Sci. 22, 1101e1106. Kumar, V., Ladha, J.K., 2011. Direct seeding of rice: recent developments and future research needs. Adv. Agron. 111, 297e413. Mahajan, G., Chauhan, B.S., 2013. Herbicide options for weed control in dry-seeded aromatic rice in India. Weed Technol. 27, 682e689. Mahajan, G., Chauhan, B.S., Johnson, D.E., 2009. Weed management comparison in aerobic in Northwestern Indo-Gangetic Plains. J. Crop Improv. 23, 366e382. Mahajan, G., Chauhan, B.S., Gill, M.S., 2011. Optimal nitrogen fertilization timing and rate in dry-seeded rice in northwest India. Agron. J. 103, 1676e1682. Mahajan, G., Chauhan, B.S., Timsina, J., Singh, P.P., Singh, K., 2012. Crop performance and water- and nitrogen-use efficiencies in dry-seeded rice in response to irrigation and fertilizer amounts in northwest India. Field Crops Res. 134, 59e70. Maity, S.K., Mukherjee, P.K., 2008. Integrated weed management in dry direct seeded rainy season rice (Oryza sativa). Indian J. Agron. 53, 116e120. Mazid, M.A., Jabber, M.A., Mortimer, M., Wade, L.J., Riches, C.R., Orr, A.W., 2003. Improving rice-based cropping systems in north-west Bangladesh: diversification and weed management. In: The BCPC International Congress, Crop Production and Protection, pp. 1029e1034. Phoung, L.T., Denich, M., Vlek, P.L.G., Balasubramanian, V., 2005. Suppressing weeds in direct-seeded lowland rice: effects of methods and rates of seeding. J. Agron. Crop Sci. 191, 185e194. Rao, A.N., Johnson, D.E., Sivaprasad, B., Ladha, J.K., Mortimer, A.M., 2007. Weed management in direct-seeded rice. Adv. Agron. 93, 153e255. Sharma, A.R., 1997. Effect of integrated weed management and nitrogen fertilization on the performance of rice under flood-prone lowland conditions. J. Agric. Sci. 129, 409e418. Singh, S., Bhushan, L., Ladha, J.K., Gupta, R.K., Rao, A.N., Sivaprasad, B., 2006. Weed management in dry-seeded rice (Oryza sativa) cultivated in the furrow-irrigated raised-bed planting system. Crop Prot. 25, 487e495. Singh, I., Ram, M., Nandal, D.P., 2007. Efficacy of new herbicides for weed control in transplanted rice under rice-wheat system. Indian J. Weed Sci. 38, 28e31. Subhas, C., Jitendra, P., 2001. Effect of rice (Oryza sativa L.) culture, nitrogen and weed control on nitrogen competition between scented rice and weeds. Indian J. Agron. 46, 68e74. Suria, A.S.M.J., Juraimi, A.S., Rahman, M.M., Man, A.B., Selamat, A., 2011. Efficacy and economics of different herbicides in aerobic rice system. Afr. J. Biotechnol. 10, 8007e8022. Taylor, M., 2007. New weed management options for Australian rice. IREC Farmers Newsl. 177, 41e43. Timsina, J., Connor, D.J., 2001. Productivity and management of rice-wheat cropping systems: issues and challenges. Field Crops Res. 69, 93e132. Tuong, T.P., Bouman, B.A.M., 2003. Rice production in water-scarce environments. In: Kijne, J.W., Barker, R., Molden, D. (Eds.), Water Productivity in Agriculture: Limits and Opportunities for Improvements. CABI Publishing, Wallingford, UK, pp. 53e67. Weerakoon, W.M.W., Mutunayake, M.M.P., Bandara, C., Rao, A.N., Bhandari, D.C., Ladha, J.K., 2011. Direct-seeded rice culture in Sri Lanka: lessons from farmers. Field Crops Res. 121, 53e63. Weiner, J., Griepentrog, H.W., Kristensen, L., 2001. Suppression of weeds by spring wheat Triticum aestivum increases with crop density and spatial uniformity. J. Appl. Ecol. 38, 784e790. Yaduraju, N.T., Mishra, J.S., 2004. Weed management in rice with special orientation to export. In: SAARC Rice Expo 2004, Maharashtra Chamber of Commerce and Industry and Rice Exporters Association of Pakistan, Mumbai, India, pp. 111e115.