Bangladesh Agron. J. 2023, 26(1): 56-74 EFFICACY OF HERBICIDE MIXTURES FOR TRANSPLANTED AMAN RICE IN SILTY CLAY LOAM SOIL OF BANGLADESH Zobayra Haque Jame1, Taslima Zahan2, H. M. M. Tariq Hossain1, Promita Shikha Roy3 and Sheikh Muhammad Masum1* 1Department of Agronomy, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh 2On-farm Research Division, BARI, Gazipur-1701, Bangladesh 3Baligaon Amzad Ali College, Tongibari, Munshigonj, Bangladesh *Corresponding author, Email: smmasum607@yahoo.com (Received: 13 July 2023, Accepted: 30 August 2023) Keywords: Chemical control, Mixture herbicide, Rice, Weed, Yield Abstract Weed management plays an important role in obtaining target yield. A field experiment was carried out at the Agronomy field of Sher-e-Bangla Agricultural University, Dhaka, Bangladesh, from July to December 2019 to get the most effective weed control strategy for transplanted Aman rice. The soil of the study field was silty clay loam in nature. The study consisted of two factors i.e., variety (4: Chinigura, BR11(Mukta), BRRI dhan56, and BRRI hybrid dhan6) and herbicide (4) viz., Bispyribac-sodium WP @ 150 g ha-1, Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1, Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1, and weedy check as a control. The experiment was laid out in a split-plot design with three replications. Thirteen weed species were found in the experimental plots, mostly broadleaf and sedge. Monochoria vaginalis was the most dominant weed species. The study noticed that the application of mixed herbicides offered better weed control over single herbicide application. Application of Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 significantly reduced weed density and biomass and was the best way of controlling complex weed flora. The study marked out BR11 (Mukta) as the most potential aman rice variety to produce the highest yields at applying Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1. This treatment gave the highest gross return (Tk. 1,46,010), net return (Tk. 88,699), and benefit- cost ratio (2.55). Therefore, the study suggests the application of mixed herbicides and BR11 (Mukta) to get the optimum yield of transplanted Aman rice and maximum economic benefit. Introduction Rice (Oryza sativa L.) is Bangladesh's major growing crop, mostly grown in three seasons viz. Aus (Pre-monsoon), Aman (Monsoon or rainy season) and Boro (Dry season) rice. Among the three growing seasons, the area coverage of Aman rice is the highest (67% of the cropped area of 85.77 hectares). In 2020, the amount of land used for HYV varieties was 44.47 lakh (4.44 million) hectares, hybrid 2.40 lakh (0.24 million) hectares, local varieties 7.15 lakh (0.75 million) hectares, and for broadcast Aman 3.12 lakh (0.31 million) hectares of cultivable land. The total land under the Aman rice was 57.14 lakh (5.71 million) hectares (Magzter, 2021). In 2019–20, about 88% was planted to modern varieties, with traditional landrace varieties covering 12% (BBS, 2019). The average rice yield of Bangladesh is almost 50% less than the world's average yield (Rahman et al., 2023). Therefore, to boost rice yield and production, attempts must be made to increase the yield per unit area by adopting modern rice varieties and applying improved technology and management practices (such as irrigation, spacing, weed, insect, etc.) Weed is the most important threat to the upland or aerobic rice systems, resulting in yield losses between 30 and 98% (Ramana et al., 2014). The high competitive ability of weeds exerts a serious negative effect on crop production. Among the harmful pest, weeds contribute to maximum losses in crop production, potentially reducing crop production by 34%, followed by animal pests (18%) and pathogens by 16% (Abbas et al., 2018). Although hand weeding is a Performance of herbicide mixture for T.Aman rice 57 popular weed control method, the unavailability of labour during the peak period discourages farmers from choosing this method. Mechanical weeding and chemical weed control are the alternatives to hand weeding. In the last few years, chemical weed control has increased (Ahmed et al., 2014) because of getting quick and site-specific weed control at a low cost compared to traditional control methods (Zahan et al., 2018). Using herbicides is a promising alternative for controlling weeds (Rahman, 2016). However, continuous and indiscriminate use of herbicides may alter their degradation and pose persistence problems due to residual effects beyond harvest, threatening health and ecology. The use of herbicides with different modes of action and chemistry is desirable to reduce the problem of residue build-up, a shift in weed flora (Rajkhowa et al., 2006), and the development of herbicide resistance in weeds (Rao et al., 2007). Herbicide mixture may be one option for managing or delaying cross-resistance development in weeds against herbicides (Dhawan et al., 2009). Different pre-mix and tank-mix combinations are being tried to control mixed types of weeds in one go (Yadav et al., 2008), reducing the total volume of herbicide and easing and economizing its application. Zahan et al. (2021) found that sole dependence on herbicides having a single mode of action is not advisable. It can contribute to weed species shifting towards difficulty to control and the rapid evolution of multiple herbicide resistance, which threatens wheat production. Bharat and Kachroo (2007) reported that tank mix application of fenoxaprop+ metribuzin (120+100 g ha−1, sulfosulfuron + 2, 4-D (25 + 500 g ha−1), clodinafop + metsulfuron methyl (60+2 g ha−1, isoproturon + 2, 4-D (1000 + 500 g ha−1) and metribuzin (175 or 200 g ha−1) significantly reduced both grass and broadleaf weeds. Applying two or more herbicides simultaneously, using pre-package mixtures, or mixing different herbicide products before the applications, is a prevalent approach in chemical weed control. Some mixed herbicides are usually available in our country and worldwide, such as bensulfuron methyl + acetachlor, bensulfuron methyl + pretilachlor, bensulfuron methyl + butachlor, bensulfuron methyl + mefenacet, bensulfuron methyl + quinclorac, bensulfuron methyl + cyhalofop-butyl + fecoxaprop-p-ethyl, bispyribac sodium, butachlor + propanil, carfentrazone- ethyl + isoproturon, ethoxysulfuron + fluazifop-p-ethyl, fenoxaprop-p-ethyl + ethoxysulfuron, etc (BCPA, 2020). Currently, the use of mixed herbicides against weeds in transplanted Aman rice has increased its effectiveness daily. Rice varieties colossally affect the development and pervasion of weeds in the field. Typically short-height varieties face more weed infestation than taller ones (Tshewang et al., 2016). Thus, an appropriate variety ought to be chosen to keep away from the weed rivalry and get the greatest yield from rice. High-yielding rice varieties are now more available than conventional ones (Shew et al., 2019). Even the growth process of rice plants under different agro-climatic conditions differs with rice varieties (Alam et al., 2012). Moreover, Zahan et al. (2017) reported that the response of transplanted Aman rice varieties differs with herbicides. Therefore, the performance of herbicides also could vary with the Aman rice varieties. Some herbicide mixtures have been launched in Bangladesh for wide-spectrum weed control in transplanted rice. But the information on their efficacy against weeds in transplanted rice varieties is very meager in the literature. Therefore, the study evaluated the performance of transplanted Aman rice varieties and found the most efficient mixed herbicide(s) with the best yield providing Aman rice varieties. Materials and Methods The study was done at the Agronomy field of Sher-e-Bangla Agricultural University (SAU), Dhaka, Bangladesh. The experimental site is geographically situated at 23°77ʹ N latitude and 90°33ʹ E longitude at an altitude of 8.6 meters above sea level. The experimental field belongs to the Agro-Ecological Zone (AEZ) of “The Modhupur Tract”, AEZ-28. The land was fairly leveled highland. The soil of the experimental site was silty clay loam in texture belonging to the Tejgaon 58 Jame et al. series having pH 5.8–6.5 and ECE 25–28 at 0-15 cm soil depths. The experiment was conducted in the rainy (Aman) season from July to December 2019. Usually, the experimental site was under the subtropical climate and was characterized by high temperature, high humidity, and heavy precipitation with occasional gusty winds from March to August; however, scanty rainfall was associated with moderately low temperature. The detailed meteorological data of monthly averaged maximum and minimum temperature, relative humidity, and total rainfall during the experimentation period are given in Table 1. Table 1. Monthly average of maximum and minimum temperature and the monthly total rainfall during the study period (July to December 2019) Month Air temperature (˚C) Relative humidity (%) Total Rainfall (mm) Maximum Minimum July’19 32.6 26.8 81 114 August’19 32.6 26.5 80 106 September’19 32.4 25.7 80 86 October’19 31.2 23.9 76 52 November’19 29.6 19.8 53 00 December’19 28.8 19.1 47 00 Source: Metrological Centre, (Climate Division), Bangladesh Meteorological Department, Agargaon, Dhaka The study considered two factors as treatments, i.e., variety 4: Chinigura, BR11(Mukta), BRRI dhan56, and BRRI hybrid dhan6 and herbicide 4: Bispyribac-sodium WP @ 150 g ha−1, Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha−1, Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha−1, and weedy check as a control. The experiment was laid out in a split- plot design with three replications. In the main plot, there was herbicide treatment, and variety was in the subplot. There were 16 treatment combinations and 48 unit plots. The unit plot size was 5.04 m2 (2.8 m×and 1.8 m). The blocks and unit plots were separated by 1.0 m and 0.50 m spacing, respectively. Herbicides were applied to each plot at par with the treatment requirement by a knapsack hand sprayer. In the case of weedy check plots, weeds were allowed to grow along with the crop throughout the crop season and no control measures were adopted to check the weeds. The weed flora present in the weedy check plots was noted. The tested varieties' healthy and disease-free seeds were collected from Bangladesh Rice Research Institute (BRRI). Before raising seedlings, sprouted seeds of all the rainy season (Aman) rice varieties were planted in the seedbeds, and 25-day old seedlings were transplanted in the main field on July 8, 2019 following the standard procedures. Detailed information on the tested herbicides is given in Table 2. Table 2. Details of the tested herbicides in aman rice Herbicide Trade name with registered company Mode of action Rate of application Time of application (DAT) Bispyribac-sodium Xtrapower 20WP; ACI Crop Care Ltd. Inhibits plant amino acid synthesis – Acetohydroxyacid synthase (AHAS) 150 g ha−1 20 Acetochlor 14% + Bensulfuron methyl 14% Ayna plus-18WP; Jass Agro Ltd. Inhibits cell division in the shoots and roots of the plant 750 g ha−1 12 Pretilachlor 6% + Pyrazosulfuron 0.15% UPLEROS; ACI Crop Care Ltd. Inhibits acetolactate synthase 9.88 kg ha−1 3 The experimental land was fertilized with N, P, K, S, and Zn at 69, 20, 35, 11, and 2 kg ha-1 in the forms of urea, triple super phosphate, muriate of potash, gypsum, and zinc sulphate, respectively. All of the fertilizers except urea were applied as basal doses at the time of final land preparation. Urea was applied in three equal splits: the first split at 21 days after transplanting (DAT), the second split was top dressed at 45 DAT (active vegetative stage), and the third split was applied at 60 DAT (panicle initiation stage). Irrigation was provided up to 5 cm in each plot Performance of herbicide mixture for T.Aman rice 59 according to the critical stages of rainy season rice. Regular observations were made to see the growth and visual differences of the crops due to the treatments applied in the experimental field. Weed density and dry matter were recorded from 1 m2 of the area at 30 and 60 days after transplanting of rainy season rice. After counting the numbers, fresh weeds were oven dried at 80° C until a constant weight was obtained. The sample was then transferred into desiccators and allowed to cool down to room temperature, and the final weight of the sample was taken. Relative weed density, weed control efficiency (WCE), weed control index (WCI), crop growth rate (CGR; mg cm-2 day-1), relative growth rate (RGR; mg g-1 day-1), and net assimilation rate (NAR; mg cm-2 day-1) were calculated following the below-mentioned formula. (i) Relative weed density (%) = Number of individuals of same species Number of individual of all species × 100 (Mishra, 1968) (ii) WCE = Weed population in control−weed population in treated plot Weed population in control × 100 (Mani et al., 1973) (iii) WCI = Weed dry weight in control−weed dry weight in treated plot Weed dry weight in control × 100 (Mishra and Tosh, 1979) (iv) Crop growth rate (CGR) = 𝑊2−𝑊1 𝑃(𝑡2−𝑡1) (Watson, 1956) Where, P = ground area (cm-2), W1 = dry weight per unit area at t1, W2 = dry weight per unit area, at t2, t1 = time of first sampling, t2 = time of second sampling (v) Relative growth rate (RGR) = 𝐿𝑛(𝑊2)−Ln(𝑊1) (𝑡2−𝑡1) (Beadle, 1985) Where, Ln = natural log values, W1 = dry weight per unit area at t1, W2 = dry weight per unit Area, at t2, t1 = time of first sampling, t2 = time of second sampling (vi) Net assimilation rate (NAR) = (𝑊2−𝑊1)( LnLA2−LnLA1) (𝑡2−𝑡1)( LnLA2−LnLA1) (Gregory, 1926) Where, LA1 = leaf area of first sampling, LA2 = leaf area of second sampling, W1 = dry weight per unit area at t1, W2 = dry weight per unit area at t2, t1 = time of first sampling, t2 = time of second sampling, Ln = natural log values Dry matter accumulation in rice plant (g) was recorded at 30, 45, 60, and 90 DAT. The sample plants were oven-dried for 72 hours at 70°C, and then data were recorded from randomly selected plant samples plant−1 plot−1. The crop was manually harvested at the maturity of grains (when 80–90% of the grains were golden yellow). The harvesting dates of Chinigura, BR11, BRRI dhan56, and BRRI hybrid dhan-6 were November 29, 2019, November 22, 2019, November 08, 2019, and November 15, 2019, respectively. Data on yield contributing characters were collected from ten (10) pre-selected hills plot−1 before harvesting the whole plot crop. Grain and straw yields were recorded from the central area of 1 m2 of each plot and finally converted to t ha−1 after adjusting grain moisture content at 12%. The straw yield was recorded after sun-drying the straws properly. For cost and return analysis, input costs, overhead costs, and some common costs were considered (Mian and Bhuiya, 1977). In the input costs, all material costs and non-material costs were taken into consideration. In a day 8 working hours was considered for labour as a man's day with 400 Tk. wage labour−1 day−1. The mechanical labour came from the tractor. A period of eight working hours for a tractor was taken to be tractor day. In the case of overhead cost, the value of land was taken Tk. 200000 ha−1. The interest on this cost was calculated for 6 months @ Tk. 12.5% per year based on the interest rate of the bank. The common cost was 5% of the total cost. The total cost of production, gross return, net return, and benefit-cost ratio was calculated from the following formula. 60 Jame et al. Total cost of production (Tk. ha−1) = Input costs (Tk. ha−1) + Overhead costs (Tk. ha−1) + Common cost (Tk. ha−1) Gross return from rice (Tk. ha−1) = Value of grain yield (Tk. ha−1) + Value of straw (Tk. ha−1) Net return (Tk. ha−1) = Gross return (Tk. ha−1) – Total cost of production (Tk. ha−1) Benefit cost ratio (BCR) = Grossreturn (Tk/ha) Cost of production (Tk/ha) The collected data were compiled and analysed statistically using the analysis of variance (ANOVA) technique with the help of a computer package program named Statistix 10 Data analysis software and the mean differences were adjusted by the Least Significant Difference (LSD) test at 5% level of probability. Results and Discussion The experimental field was infested by thirteen weed species with three grasses, three sedges, and seven broadleaf weed species and the most dominating species were broadleaf and sedge weeds (Table 3). These weed species were belonging to the nine families of Alismataceae, Menyanthaceae, Asteraceae, Sphenocleaceae, Pontederiaceae, Onagraceae, Papayeraceae, Cyperaceae, and Poaceae. The grasses were E. cruss-galli, Eleusine indica, and E. colona, sedges were Scirpus maritimus, Cyperus diformis and C. rotundus, and broadleaved were, Sagittaria guayansis, Nymphoides cristatum, Enydra fluctuans, Sphenoclea zeylanica, Monochoria vaginalis, Ludwigia octovalvis, and Marsilea quadrifolia. Bhuiyan, and Mahbub (2020) reported infestation of two types of grass, two sedges, and four broadleaves in the rice field belonging to the families of Poaceae, Cyperaceae, Pontederiaceae, Marsileaceae, Sphenocleaceae, and Asteraceae. The broadleaf weed species were M. vaginalis, Marsilea minuta, S. zeylanica, and Eclipta alba, grasses were E. crus-galli, Cynodon dactylon, and sedges were C. difformis, and Scirpus maritimus. Yadav et al. (2008) also reported that the major associated weeds in rice field were E. glabrescens, and E. colona (L.) among grasses, Ammannia baccifera L. and Euphorbia sp. among broad-leaved weeds, and Fimbristylis miliacea (L.) Vahl, Cyperus iria L., C. rotundus L., and C. difformis L. among sedges. Bari et al. (1995) reported that the three important weeds of transplanted aman rice fields were F. miliacea, Paspalum scrobiculatum, and Lyperus rotundus. Mamun et al. (1993) also reported that F. miliacea, Lindernia antipola, and Eriocaulen cenerseem were important weeds in transplant Aman rice fields. Table 3. Weed flora of the experimental field in Aman season during 2019 Local name English name Scientific name Family Habitat Weed type Chapra Goose grass Eleusine indica Poaceae Annual Grass Choto shama Jungle rice Echinochloa colona Poaceae Perennial Grass Boro shama Barnyard grass Echinochloa crus-galli Poaceae Annual Grass Holde mutha Yellow nutsedge Cyperus diformis Cyperaceae Perennial Sedge Mutha Nutsedge Cyperus rotundus Cyperaceae Perennial Sedge Cechra Dwarf Club-rush Scirpus maritimus Cyperaceae Perennial Sedge Shusni shak European water clover Marsilea quadrifolia Papayeraceae Perennial Broadleaf Chadmala Duck weed Sagittaria guayansis Menyanthaceae Perennial Broadleaf Helenca Buffalo spinach Enydra fluctuans Asteraceae Annual Broadleaf Jheel-morich Gooseweed Sphenoclea zeylanica Sphenocleaceae Annual Broadleaf Choto Pani kochu Pickerel weed Monochoria vaginalis Pontederiaceae Perennial Broadleaf Pani Long Mexican Primrose Willow Ludwigia octovalvis Onagraceae Perennial Broadleaf Species-wise weed population (No. m-2) and relative weed density (%) at 30 DAT and 60 DAT showed that there was a predominance of broadleaf and sedge weeds in weedy check plots (Table 4). M. vaginalis was the most dominant weed (36 or 18 m-2 and 15.93, 16.98 %) at 30 and 60 DAT followed by S. guayansis and C. rotundus weed species at 30 and 60 DAT. While Performance of herbicide mixture for T.Aman rice 61 the dominancy of S. maritimus at least at 30 DAT and M. quadrifolia at 60 DAT was the least among all the weed species. Table 4. Species wise weed population (No. m-2) and relative weeds density (%) in weedy check plots at 30 and 60 DAT Scientific name Weed population (No. m−2) Relative weeds density (%) 30 DAT 60 DAT 30 DAT 60 DAT Sagittaria guayansis 31 12 13.72 11.32 Enydra fluctuans 18 8 7.96 7.55 Sphenoclea zeylanica 22 9 9.73 8.49 Monochoria vaginalis 36 18 15.93 16.98 Ludwigia octovalvis 17 9 7.52 8.49 Marsilea quadrifolia 7 2 3.10 1.89 Scirpus maritimus 5 4 2.21 3.77 Eleusine indica 10 6 4.43 5.66 Echinochloa colona 13 9 5.75 8.49 Cyperus diformis 23 9 10.18 8.49 Cyperus rotundus 27 12 11.95 11.32 Echinochloa crus-galli 7 3 3.10 2.83 Weed density and dry matter Effect of herbicides was significant on weed density and dry matter at 30 and 60 DAT of rainy (Aman) season rice (Figure 1). Results revealed that the highest weed density (26 and 14 m−2 at 30 and 60 DAT) and maximum weed dry matter (8.02 and 5.36 g m-2 at 30 and 60 DAT) was recorded in weedy check plot. On the other hand, acetochlor 14% + bensulfuron methyl 4% WP treated plot had the lowest weed density (2.33 and 1.78 m-2 at 30 and 60 DAT) and minimum weed dry matter (1.78 and 1.00 g m−2 at 30 and 60 DAT). This was due to the application of acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha−1 mix herbicide which might have prevented the germination of susceptible weed species and also reduced the growth of germinated weeds by inhibiting the process of photosynthesis comparable to other herbicide treatments. Earlier studies also reported maximum weed density and dry matter in untreated weedy checks (Mishra, 2019; Suryakala et al., 2019). Application of a mixture of herbicides offered 80% or even more control of annual and perennial weeds comparable to a single application of herbicide in the previous studies (Mahbub and Bhuiyan, 2018). Fig. 1. Effect of herbicide on (A) weed density and (B) weed dry matter at 30 and 60 days after transplanting of rainy (aman) season rice (Here, H0=Weedy check, H1=Bispyribac sodium WP @ 150 g ha−1, H2=Acetochlor 14%+ Bensulfuron methyl 4% WP @ 750 g ha−1 and H3=Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha−1) a a b b d d c c 0 10 20 30 30 DAT 60 DAT W ee d d en si ty m -2 H0 H1 H2 H3 a ab bd d c c 0 2 4 6 8 10 30 DAT 60 DAT W ee d d ry w ei g h t (g m -2 ) H0 H1 H2 H3(B) (A) 62 Jame et al. Fig. 2. Effect of variety on weed density and weed dry matter at 30 and 60 days after transplanting of rainy (aman) season rice (Here, V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6) The variety had a significant effect on weed density and weed dry matter at 30 DAT and 60 DAT of rainy season rice (Fig.2). The highest weed density m-2 (16.92 and 8.08 m-2 at 30 and 60 DAT) and maximum weed dry matter (5.92 and 3.40 g m-2 at 30 and 60 DAT) was counted from the Chinigura rice variety. Minimum weed density (10.19 and 4.95 m-2 at 30 and 60 DAT) and dry matter (3.22 and 1.61 g m-2 at 30 and 60 DAT) were observed in BR 11 rice variety. The reason for getting a lower number of weeds in the high-yielding cultivar might be due to the vigorous growth of the cultivar helping to suppress weeds. Afrin et al. (2015) also reported that competitive rice varieties viz., hybrids, usually have better vigour than inbreeds and effectively suppress the infestation of weed populations or density. The interaction effect of herbicide and variety was significant on weed density and dry matter at 30 and 60 DAT (Table 5). Table 5. Combined effect of herbicide and rice variety on weed density and weed dry weight m-2 of T. Aman rice at 30 and 60 DAT Treatment Weed density (m-2) Weed dry weight (g m-2) 30 DAT 60 DAT 30 DAT 60 DAT H0V1 29.67±1.19a 16.34± 0.82a 9.70±0.39a 7.08±0.35a H0V2 20.00±0.8d 12.13±0.61c 6.51 ±0.26d 3.68±0.18d H0V3 27.33±1.09b 13.87±0.69b 9.27±0.37b 5.97±0.3b H0V4 25.00 ±1 c 12.3 ±0.62c 6.580±0.26d 4.71±0.24b H1V1 24.66±0.99c 7.33±0.37d 8.03±0.32c 2.73 ±0.14e H1V2 15.33 ± 0.61e 4.67±0.23g 4.01±0.16f 1.35±0.07h H1V3 23.33 ±0.93c 7.67±0.38d 5.83±0.23e 2.48±0.12ef H1V4 16.67 ± 0.67e 5.33±0.27f 4.12±0.16f 1.85±0.09g H2V1 4.33 ± 0.17h 3.66±0.18h 3.10±0.12g 1.79±0.09g H2V2 0.11 ± 0.01i 0.33±0.02k 0.81±0.03g 0.39±0.02j H2V3 4.33±± 0.17h 3.67±0.18h 1.86 ± 0.07i 1.02±0.051i H2V4 3.67 ± 0.15h 1.66±0.08j 1.31±0.05k 0.81±0.04i H3V1 9.01 ±0.36fg 4.99±0.25fg 2.85±0.11h 1.98±0.1g H3V2 5.33 ± 0.21h 2.66±0.13i 1.54±0.06jk 1.01±0.05i H3V3 9.34 ± 0.37f 6.00±0.3e 2.64±0.11h 2.40±0.12f H3V4 7.34 ±0.29g 2.99±0.15i 1.77±0.07ij 1.31±0.07h SE 0.88 0.23 0.11 0.13 CV (%) 7.67 4.36 3.18 6.15 In a column means having a similar letter(s) are statistically similar and those having a dissimilar letter(s) differ significantly at a 0.05 level of probability. Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14%+ Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1; V1 = Chinigura, V2 = BR 11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 a a c d a b b c 0 10 20 30 30 DAT 60 DAT W ee d d en si ty m -2 V1 V2 V3 V4 a ad d b bc c 0 2 4 6 8 30 DAT 60 DAT W ee d d ry w ei g h t (g m -2 ) V1 V2 V3 V4(b)(a) Performance of herbicide mixture for T.Aman rice 63 The results revealed that Chinigura variety had the highest weed density (29.67 and 16.34 m-2 at 30 and 60 DAT) and maximum dry matter (9.70 and 7.08 g m−2 at 30 and 60 DAT) in the weedy check plots. While application of mixed herbicide, i.e., acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha−1 in BR11 variety had the lowest weeds density (0.11 and 0.33 m−2 at 30 and 60 DAT) and minimum weed dry weight (0.86 and 0.39 g m-2 at 30 and 60 DAT). The variation in weed density and dry matter was due to the effective weed control offered by mixing herbicides and high-yielding rice cultivars compared to application of single herbicide with low-yielding rice varieties. Weed control efficiency and Weed control index Application of herbicides significantly affects the weed control efficiency (WCE) and weed control index (WCI) of T. Aman rice at 30 and 60 DAT (Figure 3). Due to herbicide treatments, WCE ranged from 22.1 to 88.9% and WCI ranged from 32.4 to 82.5% over the weedy check plots. Application of acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 offered higher WCE and WCI than the other treatments. However, all the herbicide treatments suppressed weeds, but the magnitude of suppression was higher in acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 treated plots (WCE: 88.9 and 83.7 % and WCI: 78.7 and 82.5% at 30 and 60 DAT, respectively). The weedy check plot obtained the minimum WCE and WCI (0.0 % at both 30 and 60 DAT). The differences in WCE and WCI of the herbicide treatments were due to the variations in weed density in treated plots that directly reflected the effect of herbicides on weeds. Herbicides deteriorate the physiological and morphological features of weeds, help to reduce weed density and biomass, and increase weed control efficiency (Bhuiyan and Mahbub, 2020) and weed control index (Suryakala et al., 2019). In the earlier study, Mishra (2019) found that the weed control efficiency was higher with the application of Bensulfuron methyl 60g ha-1 + Pretilachlor 600 g ha-1 at 3 DAT than hand weeding, which varies from 74% at 30 DAT to 42.9% at 90 DAT. This might be due to the effect of weeds during the initial stages of crop growth with herbicide application. Priya and Kubsad (2013) also reported higher weed control efficiency and lower weed index in herbicide treatments than weedy check owing to lower weed dry weight, higher weed control efficiency, and lower weed index due to effective control of complex weed flora. Fig. 3. Effect of herbicide on weed control efficiency and weed control index of T. Aman rice at 30 and 60 days after transplanting (Here, H0 =Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 =Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha- 1). Rice varieties significantly affected WCE and WCI of T. Aman rice at 30 and 60 DAT (Figure 4). WCE ranged from 41.2 to 59.2%, and WCI ranged from 39.0 to 56.3% with the varieties. Experiment results revealed that cultivation of BR11 rice variety cultivation recorded the maximum WCE (49.0 and 59.2%) and WCI (50.4 and 56.3%) at 30 and 60 DAT while the cultivation of d d c c a a b b 0 20 40 60 80 100 30 DAT 60 DAT W ee d c o n tr o l e ff ic ie n cy (% ) H0 H1 H2 H3 d d c c a a b b 0 20 40 60 80 100 30 DAT 60 DAT W ee d c o n tr o l in d ex (% ) 64 Jame et al. BRRI dhan56 rice variety cultivation recorded minimum WCE (41.2 and 43.8 %) and WCI (39.0 and 50.3%) at 30 and 60 DAT. Afrin et al. (2015) also found a similar result, who reported that different rice varieties significantly influenced weed control efficiency and index. Chauhan and Johnson (2011) reported that the weed control index could be attributed to less weed biomass due to the highly competitive variety's ability to suppress weeds. Fig. 4. Effect of variety on weed control efficiency and weed control index of T. Aman rice at 30 and 60 days after transplanting (Here, V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan) The combined effect of herbicide and rice variety significantly affected WCE and WCI at 30 and 60 DAT (Table 6). Table 6. Combined effect of herbicide and rice variety on weed control efficiency (%) and weed control index (%) of T. aman rice at 30 and 60 DAT Treatment Combinations Weed control efficiency (%) Weed control index (%) 30 DAT 60 DAT 30 DAT 60 DAT H0V1 - - - - H0V2 - - - - H0V3 - - - - H0V4 - - - - H1V1 16.89±0.35h 55.12±1.84g 17.22±0.29h 61.44±1.23de H1V2 23.35±0.49g 61.50±2.05f 38.35±0.64g 63.32±1.27d H1V3 14.64±0.3h 44.73±1.49h 37.11±0.62g 58.46±1.17e H1V4 33.32±0.69f 56.81±1.89g 37.39±0.63g 60.79 ±1.22de H2V1 85.41±1.78b 77.60 ±2.59c 68.04±1f 74.72±1.49c H2V2 99.45±2.07a 97.28±3.24a 86.79±1.28a 89.31±1.79a H2V3 84.16±1.75b 73.54±2.45d 79.94±1.18b 82.92±1.66b H2V4 85.32±1.78b 86.55±2.88b 80.14±1.18b 82.87±1.66b H3V1 69.64±1.45d 69.44±2.31e 70.62±1.04e 72.03±1.44c H3V2 73.35±1.53c 78.04±2.6c 76.34±1.13c 72.65±1.45c H3V3 65.81±1.37e 56.74±1.89g 71.52±1.05de 59.80±1.2e H3V4 70.64±1.47cd 75.7±2.52cd 73.15±1.08d 72.12±1.44c SE 1.39 1.72 1.17 1.56 CV (%) 3.78 4.05 3.14 3.61 In a column means having a similar letter(s) are statistically similar and those having dissimilar letter(s) differ significantly at a 0.05 level of probabilit Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2= Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1, V1 = Chinigura, V2 = BR 11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Due to the combined effect of herbicide and rice variety, the WCE ranged from 14.64 to 99.45% and WCI ranged from 17.22 to 89.31% over the weedy check plot. Application of acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 mixed herbicide along with BR 11 c ca a d d b b 0 10 20 30 40 50 60 70 80 30 DAT 60 DAT W ee d c o n tr o l ef fi ci en cy ( % ) V1 V2 V3 V4 c ca a b db b 0 10 20 30 40 50 60 70 30 DAT 60 DAT W ee d c o n tr o l in d ex ( % ) Performance of herbicide mixture for T.Aman rice 65 rice variety recorded the maximum WCE (99.5 and 97.3%) and WCI (86.8 and 89.3%) at 30 and 60 DAT. The reason might be related to the effect of the application of acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 in BR11 that hampered weed growth and reduced weed number and biomass, and boosted up weed control efficiency and weed control index of this combined treatment. While the minimum WCE and WCI (0.0 and 0.0 %) at 30 and 60 DAT was recorded in weedy check plots along with Chinigura rice, and statistically similar results were also found in the weedy check plots along with BR11, BRRI dhan56, and BRRI hybrid dhan6 rice cultivation. Plant height Plant height is an important morphological character that acts as a potential indicator of the availability of growth resources in its approach. The study results expressed that rice plant heights significantly varied with herbicide treatments (Figure 5). The maximum plant height (40.1 cm) was recorded from acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 (H2) mixed herbicide treatment at 15 DAT which was statistically similar with bispyribac sodium (40.0 cm) and significantly superior over remaining treatments. At 30 DAT the maximum plant height (80.0 cm) was recorded from pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1which was statistically similar with (79.3 cm) acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1. The tallest plants (99.8, 117.3, 136.1, and 138.8 cm at 45, 60, and 90 DAT, and at harvest, respectively) were recorded from acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 treated plots and statistically similar results were also obtained from bispyribac sodium treated plots, pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1 treated plots, and also from bispyribac-sodium treated plots. On the other side, acetochlor 14% + bensulfuron methyl 4% WP treated plots had the shortest plants (37.34 cm) at 15 DAT which was statistically similar with pretilachlor 6% + pyrazosulfuron 0.15% WP treated plots. However, the weedy check plots had the shortest plants at 15, 45, 60, and 90 DAT, and even at harvest (72.8, 92.7, 113.3, 130.7, and 132.9 cm, respectively). At the earlier growth stage, spraying mixed herbicide in plants may produce a thin layer in the leaf surface area that might hamper photosynthesis, and as a result, dry matter accumulation and plant height get affected for a while comparable to the plants of no herbicide sprayed plots or weedy check plots. In the earlier study, Das et al. (2017) reported that the application of herbicides did not show any phytotoxic symptoms on rice plants. However, Teja et al. (2017) reported that the plant height of rice varied significantly with herbicide treatments. Fig. 5. Effect of herbicide on plant height of T. Aman rice at different days after transplanting. Here, Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14%+ bensulfuron methyl 4% WP @ 75 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1. a c c b b b a b a ab ab ab b a a a a a b a b a a ab 0 50 100 150 200 15 DAT 30 DAT 45 DAT 60 DAT 90 DAT At harvest P la n t h ei g h t (c m ) H0 H1 H2 H3 66 Jame et al. Rice plant height was significantly differed with the varieties at different days after transplanting (Figure 6). The results expressed that Chinigura had the maximum plant height (45.60, 87.67, 107.99, 130.97, 155.24, and 158.18 cm at 15, 30, 45, 60, 90 DAT, and, at harvest, respectively) while BR11 had the minimum plant height (34.31, 64.58, 74.77, 80.61, 117.76, and 119.86 cm at 15, 30, 45, 60, 90 DAT, and at harvest, respectively). The variation in plant height is probably due to the genetic makeup of the variety. Salam et al. (2020) also observed a similar result and reported that the varieties significantly influenced plant height. Fig. 6. Effect of variety on plant height of T. Aman rice at different days after transplanting Rice plant height was significantly varied with the combined effect of herbicide and variety (Table 7). Table 7. Combined effect of herbicide and variety on plant height at different after transplanting of Aman rice Treatments Days after transplanting (DAT) At harvest 15 30 45 60 90 H0V1 45±59±1.3 a 82.43±4.54 b 100.53±3.01 d 128.80±2.51 c-e 147.53± 9.31 b 149.33±6.67 c H0V2 38.30±1.09 b-d 58.53±2.12 i 72.73±2.7 h 78.67±0.7 i 116.29±3.5 g 117.07±4.26 f H0V3 37.24±1.06 c-e 73.90± 1.39 fg 101.01±6.26 d 126.87±2.7 c-f 129.58±2.7 de 134.2±2.37 de H0V4 39.16±1.12 bc 76.30±3.64 d-f 96.40±5.24 ef 118.93± 4.24 g 129.33±2.9 de 130.93±2.8 e H1V1 46.16±1.32 a 89.05± 4.16 a 109.97±4.05 ab 130.53±1.56 bc 156.30±5.19 a 157.23±5.76 b H1V2 33.33±0.95 fg 60.67± 2.75 i 78.30±2.79 g 79.27±0.89 i 120.54±3.87 fg 121.53± 5.4 f H1V3 39.59±1.13 bc 75.33± 2.27 e-g 109.23±7.66 ab 130.07±0.06 bc 131.42±3.03 c-e 133.50± 4.91 de H1V4 41.07±1.17 b 79.43±1.22 b-d 100.08±1.17 de 123.97±3.25 e-g 126.10±3.61 ef 130.40±3.64 e H2V1 44.50±1.27 a 89.83 ±3.33 a 111.83±5.93 a 130.56±1.91 bc 158.78±4.57 a 164.33±5 a H2V2 32.89±0.94 g 69.57±0.86 h 74.23±2.32 h 84.45±1.77 h 116.42±6.47 g 119.37±6.62 f H2V3 36.32±1.04 c-e 80.27±1.14 bc 106.27±6.65 bc 124.67±4.6 d-f 132.72 ±5.04 cd 133.70±5.87 de H2V4 35.65±1.02 d-g 77.40± 2.62 c-e 106.97±5.8 bc 129.31±1.46 b-d 136.43±4.1 c 137.83±4.1 d H3V1 46.17±1.32 a 89.37±2.93 a 109.62±6.96 ab 134.00±3.03 ab 158.37±0.87 a 161.81±1.92 ab H3V2 32.71±0.93 g 69.53±2.73 h 73.83±3.54 h 80.03±1.57 hi 117.79±0.51 g 121.47±1.03 f H3V3 33.97±0.97 e-g 82.50±0.75 b 104.36±4.05 c 136.07±0.37 a 133.80±0.46 cd 130.93±0.64 e H3V4 36.66±1.05 c-e 78.59±2.54 c-e 94.46 ±4.49 f 121.93±4.58 fg 132.07±0.57 cd 132.23±0.64 de SE 1.59 1.60 1.83 2.45 2.82 3.16 CV(%) 5.04 2.54 2.32 2.59 2.58 2.85 In a column means having a similar letter(s) are statistically similar and those having a dissimilar letter(s) differ significantly at a 0.05 level of probability Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14% + bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1; V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Chinigura variety had the tallest plants (46.2 cm) at 15 DAT in Pretilachlor 6% + pyrazosulfuron 0.15% WP treated plots and statistically similar height was found in bispyribac sodium treated plots (46.2 cm), weedy check plots (45.6 cm), and acetochlor 14% + Bensulfuron methyl 4% WP treated plots (44.5 cm) with the same variety. At 30, 45, 60 DAT, and even at harvest, the tallest plants were found from Chinigura variety in acetochlor 14% + Bensulfuron methyl 4% WP treated plots and also from pretilachlor 6% + pyrazosulfuron 0.15% WP treated plots and bispyribac-sodium WP treated plots. However, at 60 DAT, BRRI dhan56 had the tallest plants in pretilachlor 6% + pyrazosulfuron 0.15% WP treated plots and also from Chinigura variety a a a a a a c c d c c c b b b a b b b b c b b b 0 50 100 150 200 15 DAT 30 DAT 45 DAT 60 DAT 90 DAT At harvest P la n t h ei g h t (c m ) Days after trasnplanting V1 V2 V3 V4 Performance of herbicide mixture for T.Aman rice 67 in the pretilachlor 6% + pyrazosulfuron 0.15% WP treated plots. BR11 recorded the shortest plants from pretilachlor 6% + pyrazosulfuron 0.15% WP treated plots at 15 DAT. At 30, 45, 60, and 90 DAT, and at harvest the shortest plants (58.5, 72.7, 78.7, 116.3 and 117.1 cm, respectively) were in the weedy check plots of Chinigura variety. Dry matter accumulation (DMA), Crop growth rate (CGR), and Net assimilation rate (NAR) Application of herbicides significantly affected DMA, CGR, and NAR of T. Aman rice at 30, 45, 60 and 90 DAT (Fig. 8). The maximum DMAs (9.2, 27.5, 63.8 and 108.1 g plant−1 at 30, 45, 60 and 90 DAT, respectively), CGR (3.94 mg cm-2 day-1), and NAR (7.46 mg cm-2 day- 1) were recorded in acetochlor 14% + bensulfuron methyl 4% WP treated plots. The minimum DMAs (5.7, 20.9, 49.5, and 90.3 g plant-1 at 30, 45, 60, and 90 DAT respectively) and CGR (3.63 mg cm-2 day-1) were found in weedy check plots. The minimum NAR (6.20 mg cm-2 day-1) was recorded in Bispyribac-sodium WP treated plots. The DMA and CGR differences in herbicide- treated plots over weedy check plots were due to the reduction of weeds which ultimately helped in undisturbed plant growth by utilizing its surrounded resources. Similar result was also observed by Lodhi (2016) who reported that weed control treatments caused remarkable variations in the quantity of dry matter accumulation and crop growth rate of rice. Fig. 8. Effect of herbicide(A) and variety (B) on dry matter accumulation plant-1 of T. aman rice at 30, 45, 60 and 90 days after transplanting Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha−1, H2 = Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha−1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha−1, V1 = Chinigura, V2 = BR 11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 The dry matter accumulation (DMA) differs with the varieties due to the differences in leaf area, growth stage, and resources utilization ability of the varieties. In this study, varieties had significant effect on DMAs of T. Aman rice at 30, 45, 60 and 90 DAT and also on CGR (Fig. 8 and Figure 9). BR11 had the maximum DMAs (8.32, 32.61, 74.26 and 125.85 g plant−1, respectively) at 30, 40, 60 and 90 DAT and the maximum CGR (4.59 mg cm−2 day−1). While Chinigura rice had the minimum DMAs (7.18, 15.42, 39.27, and 72.95g plant−1 at 30, 40, 60 and 90 DAT, respectively) and the minimum CGR (2.99 mg cm−2 day−1). Usually, high yielding or hybrid varieties have competition, weed suppression, and resource utilization ability greater than the local varieties that influence dry matter accumulation. The results of this study are aligned with Nahida et al. (2013), who reported that dry matter (DM) accumulation over time considerably varied with the varieties, and also with the study of Mia and Shamsuddin (2011), who reported that the higher CGR is related to higher leaf area index and net assimilation rate. The combined effect of herbicide and rice variety was significant on DMA (Table 8) and (Table 9) CGR. The maximum dry matter accumulations (10.3, 37.5, 84.4, and 138.8 g plant-1, at 30, 45, 60, and 90 DAT, respectively) and CGR (4.83 mg cm−2 day−1) were recorded in Acetochlor 14% + Bensulfuron methyl 4% WP treated plots of BR11. In weedy check plots, d b b b c a a a a a a a b a a a 0 50 100 150 30 DAT 45 DAT 60 DAT 90 DAT D ry m a tt er a cc u m u la ti o n (g p la n t-1 ) H0 H1 H2 H3 b c c d a a a a b b b c a a a b 0 50 100 150 30 DAT 45 DAT 60 DAT 90 DAT V1 V2 V3 V4A B 68 Jame et al. Chinigura rice had the minimum CGR (2.76mg cm-2 day−1) and minimum dry matter accumulation at 30 DAT (5.32 g plant−1). DMAs at 45 and 60 DAT were minimum (12.2 and 33.9 g plant−1) in Bispyribac- sodium treated plots of Chinigura rice. Table 8. Combined effect of herbicide and rice variety on dry matter accumulation at 30, 45, 60, and 90 days after transplanting of T. Aman rice Treatment Dry matter accumulation (g plant−1) 30 DAT 45 DAT 60 DAT 90 DAT H0V1 5.32±2.2 i 13.80±1.2 g 34.99±0.6 g 66.00±0.8 h H0V2 6.14±1.3 gh 26.11±0.4 e 60.05±1 d 108.07±1.2 f H0V3 5.58±0.5 hi 16.70±2.1 f 40.74±0.7 f 76.51±0.9 gh H0V4 5.58±4.8 hi 27.16±4.1 e 62.34±1.2 d 110.55±1.3 e H1V1 7.24±3.1 f 12.20±3.7 g 33.89±0.6 g 66.00±0.8 h H1V2 8.14±2.9 e 31.28±3.3 d 72.61±1.2 c 123.43±1.2 bd H1V3 6.71±3.9 fg 3237±4.3 cd 73.82±1.3 c 119.1±1.4 ce H1V4 8.29±5.1 d 32.88±1.9 cd 75.57±1.3 bc 114.69±1.5 de H2V1 8.91±1.3 cd 18.13±2.1 f 45.33±0.8 ef 80.78±0.9 g H2V2 10.26±1.9 a 37.45±1.4 a 84.40±1.4 a 138.76±1.5 a H2V3 8.27±2.2 d 18.72±1.7 f 46.23±0.8 e 82.57±0.9 g H2V4 9.48±1.4 bc 35.56±1.5 ab 79.28±1.3 ab 130.4±1.5 ab H3V1 7.24±1.8 f 17.55±2.4 f 42.93±0.7 ef 79.04±0.9 g H3V2 8.74±0.4 cd 35.58±0.8 ab 79.97±1.3 ab 133.1±1.5 ab H3V3 6.78±0.5 fg 18.58±2.5 f 45.19±0.8 ef 82.15±0.9 g H3V4 9.84±0.7 abg 34.24± 2.6 bc 76.5±1.3 bc 126.44±1.4 bc SE 0.35 1.21 2.54 5.09 CV (%) 5.73 5.84 5.21 6.10 In a column means having a similar letter(s) are statistically similar and those having a dissimilar letter(s) differ significantly at a 0.05 level of probability Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha−1, H2 = Acitachlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha−1; V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Table 9. Combined effect of herbicide and rice variety on crop growth rate and net assimilation rate of T. aman rice Treatments Crop growth rate (mg cm−2 day−1) Net assimilation rate (mg cm−2 day−1) H0V1 2.76±0.11g 6.04±0.4fg H0V2 4.27±0.17c 6.44±0.43de H0V3 3.18±0.13f 5.83± 0.39g H0V4 4.29±0.17c 7.19±0.48b H1V1 2.85±0.11g 6.15±0.41e-g H1V2 4.52±0.18b 6.25±0.42ef H1V3 4.03±0.16d 7.19±0.48b H1V4 3.48±0.14e 5.22±0.39h H2V1 3.15±0.13f 7.19±0.48b H2V2 4.83±0.19a 7.93±0.53a H2V3 3.23±0.13f 6.91±0.46bc H2V4 4.55±0.18b 7.82±0.52a H3V1 3.21±0.13f 7.76±0.52a H3V2 4.73±0.19a 6.74±0.45cd H3V3 3.29±0.13f 6.05±0.4fg H3V4 4.44±0.18b 6.96±0.46bc SE 0.06 0.17 CV (%) 2.17 3.26 In a column means having a similar letter(s) are statistically similar and those having a dissimilar letter(s) differ significantly at a 0.05 level of probability Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acitachlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1; V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Performance of herbicide mixture for T.Aman rice 69 A Fig. 9. Effect of herbicide (A) and variety (B) on crop growth rate of T. Aman rice Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha−1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha−1, V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 B Fig. 10. Effect of herbicide (A) and variety (B) on net assimilation rate at 30, 45, 60, and 90 days after transplanting of T. Aman rice In a column means having a similar letter(s) are statistically similar and those having a dissimilar letter(s) differ significantly at a 0.05 level of probability Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha−1, H2 = Acitachlor 14% + Bensulfuron methyl 4% WP @ 750 g ha−1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha−1; V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Grain yield, Straw yield, and harvest index The grain and straw yields (t ha-1) and harvest index (%) of T. aman rice were significantly influenced by herbicide application, and grain yield significantly varied with the herbicide treatments (Figure 11, Fig. 12 and Figure 13). The grain and straw yields (3.25 t ha−1 and 2.26 t ha−1, respectively) and harvest index (36.0%) were the lowest in weedy check plots where weeds were allowed to grow throughout the crop growing season. The highest grain and straw yields (4.49 t ha−1 and 6.38 t ha−1, respectively) and harvest index (42.0%) were obtained from acetochlor 14% + bensulfuron methyl 4% WP, and it provided superior weed control over all other herbicide treatments. Effective mix herbicides can affect a wide range of weed species causing a reduction of weed density comparable to single or other low-effective mix herbicide applications. The similar result reported by Suryakala et al. (2019) showed that grain yield production was lower in un-weeded control, respectively indicating the importance of weed management in the critical growth period of the crop by herbicide application, which facilitated the efficient use of resources. Hossain and Mondal (2014) also reported that tank-mix application of bispyribac + ethoxysulfuron, pretilachlor fb metsulfuron-methyl + chlorimuron-ethyl and pretilachlor + bensulfuron resulted in more rice grain yield than their sole application. Mishra (2019) reported c b a a 0 1 2 3 4 5 H0 H1 H2 H3 C ro p g ro w th ra te ( m g c m -2 d a y -1 ) d a c b 0 1 2 3 4 5 V1 V2 V3 V4 c d a b 0 2 4 6 8 10 H0 H1 H2 H3 N et a ss im il a ti o n r a te (m g c m -2 d a y -1 ) a a b a 0 2 4 6 8 V1 V2 V3 V4 N et a ss im il a ti o n r a te (m g c m -2 d a y -1 ) B A 70 Jame et al. better performance of herbicide combinations in controlling weeds and increasing yield in transplanted rice. Fig. 11. Effects of herbicide and variety on grain yield of T. aman rice Here, H0 = Weedy check, H1 = Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1 V1 = Chinigura, V2 = B 11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Grain and straw yields and harvest index were significantly varied with rice varieties (Figure 11, Figure 12, and Figure 13). The maximum grain and straw yields (4.71 t ha-1 and 6.40 t ha-1, respectively) and harvest index (42.2%) were recorded from BR11 because of producing the maximum number of filled grains per panicle along with a maximum 1000-seed weight that collectively contributed to higher grain yield. While Chinigura rice had the minimum grain and straw yields (2.63 t ha-1 and 5.13 t ha-1, respectively) and harvest index (34.3%). The similar finding was reported by Islam et al. (2013) that the varieties which produced a higher number of effective tillers hill–1 and a higher number of filled grains panicle–1 also showed higher grain yield ha–1. Dutta (2002) also reported that the genotypes, which produced more effective tillers hill–1 and a higher number of grains per panicle also showed higher grain yield in rice. Grain yield was significantly influenced by the combined effect of herbicide and rice variety (Table 10). BR11 had the maximum grain and straw yields (5.57 t ha−1 and 6.76 t ha−1, respectively) and harvest index (45.1%) in acetochlor 14% + bensulfuron methyl 4% WP applied plots while Chinigura rice produced the minimum grain and straw yields (2.26 t ha−1 and 4.21 t ha−1, respectively) and harvest index (30.8%) in the weedy check plots. Fig. 12. Effect of herbicide and variety on straw yield of T. aman rice Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1 V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 d c a b 0 1 2 3 4 5 H0 H1 H2 H3 G ra in y ie ld ( t h a -1 ) c a b b 0 1 2 3 4 5 6 V1 V2 V3 V4 b b a b 0 2 4 6 8 H0 H1 H2 H3 S tr a w y ie ld ( t h a -1 ) c a b b 0 2 4 6 8 V1 V2 V3 V4 A B Performance of herbicide mixture for T.Aman rice 71 Table 10. Combined effect of herbicide and rice variety on grain and straw yields (t ha-1) and harvest index (%) of T. aman rice Treatments Grain yield (t ha−1) Straw yield (t ha−1) Harvest index (%) H0V1 2.26±0.41g 4.79±0.72e 32.00±0.86f H0V2 3.78±0.47e 5.94±0.74b-d 38.89±0.93de H0V3 3.26±0.41f 5.70±0.71cd 36.38±0.87e H0V4 3.68±0.46e 6.34±0.79a-c 36.73±0.87e H1V1 2.32±0.42g 4.21±0.74e 36.35±0.86e H1V2 4.55±0.57c 6.58±0.82ab 40.8 ±0.97b-d H1V3 3.98±0.5de 5.63±0.7d 41.42±0.97b-d H1V4 4.24±0.53cd 6.52±0.82ab 39.41±0.94 c-e H2V1 2.98±0.6f 6.71±0.86a 30.75±0.98f H2V2 5.57±0.7a 6.76±0.85a 45.09±1.07a H2V3 4.88±0.61b 6.34±0.79a-c 43.49±1.04ab H2V4 4.52±0.57c 5.72±0.72cd 44.14±1.05ab H3V1 2.94±0.49f 4.80±0.73e 37.98±0.96de H3V2 4.93±0.62b 6.32±0.79a-c 43.82±1.04ab H3V3 4.28±0.53cd 5.76±0.72cd 42.63±1.01 a-c H3V4 4.36±±0.54c 5.69±0.72cd 43.63±1.04ab SE 0.11 0.31 0.45 CV (%) 4.84 6.61 5.31 In a column means having similar letter(s) are statistically similar and those having dissimilar letter(s) differ significantly at 0.05 level of probability. Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1. V1 = Chinigura, V2 = BR11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Economic viability of different treatments combination The economic performance of treatment combinations was determined ha-1 area basis, including total cost of production, gross returns, net returns, and benefit cost ratio (profit over per taka investment) under treatments imposed (Table 11). Cost of production varied due to different herbicide applications and rice variety cultivation. The cost of production varied mainly for the herbicide application. In the case of a weedy check, there was no involvement of cost for herbicide application. In this experiment, the highest total production cost occurred in Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1 mixed herbicide application along different rice variety cultivation and lowest in weed check fields along with different rice variety cultivation. Gross return was influenced by different herbicide treatments along with different rice variety. The highest gross return (146010 taka) was recorded under Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 mixed herbicide along with BR11 while the minimum (61290 taka) in weedy check plot along with Chinigura. Net return was varied by different herbicide treatments along with different rice variety. The highest net return (88699 taka) was recorded under Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 mixed herbicide along with BR11 while the minimum (4849 taka) in Bispyribac sodium WP @ 150 g ha-1 herbicide along with Chinigura. Benefit cost ratio (BCR) The benefit cost ratio varied in different herbicide treatments along with different rice variety. The highest benefit cost ratio (2.55) was recorded under Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 mixed herbicide along with BR11 due to reason that higher grain yield (5.57 t ha-1), straw yield (6.76 t ha-1) and lower weed density (0.11) and weed biomass (0.33) per meter square were recorded under this treatment combination while the minimum (1.08) in Bispyribac-sodium WP @ 150 g ha-1 herbicide along with Chinigura. Due to reason that effective 72 Jame et al. mixed herbicide reduces wide density weed population while helping the plant to higher production due to fewer weeds competition. On the other hand, single herbicides reduce weed density of one or two species, which helps to grow others weeds, and they grow vigorously and consume more resources, resulting in poor crop plant growth. This result supports the findings of Salam et al. (2020), who reported that benefit cost ratio varied among different rice varieties. Sunil et al. (2010) also reported that pre-emergence application of bensulfuron methyl + pretilachlor (6.6 GR) @ 0.06 + 0.6 kg ha-1 + one inter cultivation at 40 DAS recorded significantly higher grain and straw yields (4425 and 5020 kg ha-1), lower weed population and dry weight (17 and 2.32 g m-2). This treatment also resulted in higher net returns and B:C ratio. Table 11. Cost of production, return and Benefit cost ratio (BCR) of T. aman rice varieties i.e, Chinigura, BR11, BRRI dhan56 and BRRI hybrid dhan6 under different treatments Treatment Combinations Fixed variable cost Herbicide application cost Total cost of production Gross return (Tk) Net return (Tk) BCR H0V1 55865 0 55865 61290 5425 1.10 H0V2 55865 0 55865 100440 44575 1.80 H0V3 55865 0 55865 87200 31335 1.56 H0V4 55865 0 55865 98340 42475 1.76 H1V1 56016 1345 57361 62210 4849 1.08 H1V2 56016 1345 57361 120330 62969 2.10 H1V3 56016 1345 57361 105130 47769 1.83 H1V4 56016 1345 57361 112520 55159 1.96 H2V1 56011 1300 57311 81210 23899 1.42 H2V2 56011 1300 57311 146010 88699 2.55 H2V3 56011 1300 57311 128340 71029 2.24 H2V4 56011 1300 57311 118720 61409 2.07 H3V1 56243 3364 59607 78300 18693 1.31 H3V2 56243 3364 59607 129570 69963 2.17 H3V3 56243 3364 59607 112760 53153 1.89 H3V4 56243 3364 59607 114690 55083 1.92 In a column means having similar letter(s) are statistically similar and those having dissimilar letter(s) differ significant ly at 0.05 level of probability. Here, H0 = Weedy check, H1= Bispyribac sodium WP @ 150 g ha-1, H2 = Acitachlor 14%+ Bensulfuron methyl 4% WP @ 750 g ha-1 and H3 = Pretilachlor 6% + pyrazosulfuron 0.15% WP @ 9.88 kg ha-1. V1 = Chinigura, V2 = BR 11, V3 = BRRI dhan56 and V4 = BRRI hybrid dhan6 Conclusion The study suggests that the application of Acetochlor 14% + Bensulfuron methyl 4% WP @ 750 g ha-1 mixed herbicide combination with BR11(Mukta) gave the maximum grain and straw yields offering the highest gross return, net return, and benefit cost ratio. However, further investigation is necessary for the other soil types under different AEZs in Bangladesh. Acknowledgement The authors acknowledged the Farm Division of Sher-e-Bangla Agricultural University to provide the input materials and Bangladesh Rice Research Institute (BRRI) to supply the quality seeds that supported us a lot to conduct the study. References Abbas, T., Z.A. Zahir, M. Naveed and R.J. Kremer. 2018. 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