Effect of different weed management techniques on the performance of wheat cultivars

Weed management in a sustainable way is the ultimate target of Agronomists to maximize crop yield per unit area. To develop a sustainable weed management technique, an experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh to study the effect of different weed management techniques on the performance of wheat cultivars. The experiment comprised three wheat cultivars; viz. BARI Gom-28, BARI Gom-29 and BARI Gom-30 and five weed management techniques namely, no weeding (W0), two hand weedings (HW) at 20 DAS and 40 DAS (W1), use of rice straw mulch @ 6 t ha (W2), use of pre emergence herbicide Panida @ 1 L ha –1 (W3) and use of pre emergence herbicide + one hand weeding (HW) at 40 DAS (W4). The experiment was laid out in a splitplot design with three replications. The experimental plots were infested by different weed species. Annual weeds were outnumbered than perennial and constitute 84.74% against 15.26%, respectively. Among them, the five most dominant weed species based on the importance value in descending order were Polygonum orientale>Chenopodium album >Cynodon dactylon>Sonchus arvensis>Cyperus rotundus and rest of the weed species represent 8.94%. Wheat cultivar BARI Gom-29 produced the highest grain yield (3.44 t ha). The highest grain yield (3.29 t ha) was obtained from the application of pre emergence herbicide Panida @ 1 L ha. But in case of interaction BARI Gom-29 in combination with use of rice straw mulch @ 6 t ha produced the highest grain yield (4.36 t ha). The highest grain yield obtained due to highest number of total and effective tillers hill and highest number of grains spike in BARI Gom-29 with application of rice straw mulch @ 6 t ha. From the results of the study it may be concluded that BARI Gom-29 with application of rice straw mulch @ 6 t ha technique appears to be the promising technology in controlling weeds as well as obtaining higher grain yield of wheat.


Introduction
Wheat (Triticum aestivum L.) is the most important cereal crop all over the world belonging to the family Poaceae.In Bangladesh wheat is the second most important staple food crop after rice.Per capita intake of wheat stands at 28-30 g/day, indicating its approximate demand at 4 million tons per annum.The facts of past three decades indicate the increasing trend of wheat consumption.To meet increasing consumers' demand, the country has to import, on an average, 1.4 million tons of wheat every year.Moreover, the total cultivable land has been decreasing day by day due to increasing population.On the other hand, farmers have the tendency to cultivate boro rice cultivation in November -April of wheat growing period.In Bangladesh, total area under wheat crop has been estimated 4,15,339 ha compared to 4,44,805 ha (BBS, 2016).Average yield rate of wheat has been estimated 3.03 metric t ha -1 which is 4.19% higher than that of last year (BBS, 2017).Though, wheat is an important cereal crop in Bangladesh, the average yield of wheat in Bangladesh is low compared to that of other wheat growing countries of the world due to lack of use of improved cultivars and appropriate management practices such as weed management techniques.
Wheat cultivars vary in their competitiveness against weeds (Christensen, 1995;Cosser et al., 1997;Lemerle et al., 2006) and those with a high degree of competitive ability, especially against aggressive weeds, are highly beneficial because they protect against the build-up of weed infestation and proliferation of the weed seed bank (Bond and Grundy, 2001;Hoad et al., 2008;Feledyn-Szewczyk et al., 2014).A review of world literature indicates that the competitiveness of wheat cultivars depends on crop density and intrinsic morphological and growth features, such as rate of growth, length of stems, tillering rate, surface and angle of leaf attachment on the wheat plant as well as any allelopathic properties (Didon, 2002;Bertholdsson, 2005;O'Donovan et al. 2005;Liatukas and Leistrumite, 2009;Feledyn-Szewczyk, 2013).Moreover, different cultivars respond differently for their genotypic characters, input requirement, growth process and the prevailing environment during growing season.For example BARI Gom-28 having ability of short duration, high yield and heat tolerant, BARI Gom-29 having short duration and leaf rust tolerant, BARI Gom-30 having short duration, tolerant to leaf blight and heat.
It is reported that weeds reduced wheat yield up to 25-30% in Pakistan (Nayyar et al., 1994), 20-40% in India (Mishra, 1997), up to 50% in Nepal (Ranjit, 2002).The number of weed species reported vary from country to country, 90 species from India (Rao, 2000), 73 species from Bangladesh (Begum et al., 2003) and 30 species from IAAS, Nepal (Dangol and Chaudhary, 1993).Hossain et al. (2010) noted that wheat fields are normally infested by 18 to 22 weed species belonging to 11-12 families.The most important weeds of wheat field in Bangladesh are Polygonum orientale, Chenopodium album, Cynodon dactylon, Sonchus arvensis and Cyperus rotundus (Huda et al., 2017).Karim (1987) estimated that weeds caused 33% yield loss of total wheat in Bangladesh, most of the plant parameters including plant height, number of tillers, number of grains spike -1 , grain weight etc. are affected by weed competition with wheat plant.It was found that weeding at 20 and 40 days after sowing (DAS) gave the highest grain and straw yields (Tariful et al., 1998).Weed control is a basic requirement and a major component of production systems (Hossain et al., 2009).However, Bangladesh farmers are not interested to control weeds in wheat fields due to labor crisis during the wheatgrowing period (WRC, 2007).Most of the annual weeds generally react very quickly to alternate their environment.Thus the best weed management techniques need to be adopted by the farmers to reduce weed infestation and maximizing wheat yield.Therefore, the present study was undertaken (i) to find out the ability of cultivar on weed suppression and yield of wheat, (ii) to analyze the effect of weed management techniques on weed suppression and yield of wheat and (iii) to determine the influence of different weed management techniques on weed suppression and yield of wheat cultivars.

Materials and Methods
The experimental site belongs to the non-calcareous dark grey floodplain soil (Old Brahmaputra Alluvial Soil Tract) under the Old Brahmaputra Floodplain Agro Ecological Zone-9.The experimental field was medium high land with loamy soil having pH value 6.5 and 1.027% organic matter.The experiment comprised three wheat cultivars viz; BARI Gom-28, BARI Gom-29 and BARI Gom-30 and five weed management techniques namely no weeding (W 0 ), two HW at 20 DAS and 40 DAS (W 1 ), use of rice straw mulch @ 6 t ha -1 (W 2 ), use of pre emergence herbicide Panida @ 1 L ha -1 (W 3 ) and use of pre emergence herbicide + one HW at 40 DAS (W 4 ).The experiment was laid out in a split-plot design with three replications where wheat cultivar were assigned to the main plot and weed management practices were assigned to the sub-plots.The unit plot size was 10 m 2 (4 m × 2.5 m).The experimental land was opened with a tractor drawn disc plough 15 days before sowing and fertilized with 200, 160, 50 and 112 kg ha -1 urea, triple superphosphate, muriate of potash and gypsum, respectively.The entire amount of TSP, MoP and gypsum and one-third of urea were applied at the time of final land preparation.The rest amount of urea was top dressed at 20 and 40 DAS.Seeds were sown in line at the rate of 140 kg ha -1 in furrows made by tine on 21 November 2016.Weeding was done as per weed management treatment and other necessary intercultural operations were done to ensure and maintain the normal growth of the crop.Data on weed density and dry weight were collected at 30 60 and 90 DAS.For determining weed density and dry weight, weeds were collected by using 0.25 m × 0.25 m quadrate.The quadrate was placed in four spots at random in each plot and all weeds inside the quadrate were collected and the number of weeds was counted.The average values were converted to number m -2 multiplying by four.Then the weeds were dried first in the sun and thereafter in an electric oven maintaining a constant temperature of 80°C for 72.Oven dry weight was expressed in g m -2 .The importance value (I.V.) of weed was expressed based on the following equation:

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The crop of each plot was harvested at maturity on 21 March 2017.It was then carried to the threshing floor for processing.The crop was sun-dried for four days and then threshed and cleaned.Observations were made on plant height, number of total tillers hill -1 , number of effective tillers hill -1 , spike length, number of total spikelets spike -1 , number of grains spike -1 , 1000-grain weight, grain yield, straw yield, biological yield and harvest index.All the collected data were statistically analyzed and the mean differences were adjudged by Duncan's Multiple Range Test (DMRT) (Gomez and Gomez, 1984).

Results and Discussion
The experimental plots of Agronomy Field Laboratory of BAU were infested with 20 weed species belonging to 12 families.Five weed species belonging to the family Poaceae, three species belonging to the family Polygonaceae, two species belonging to the family Commelinaceae and Compositae and other 10 weed species belong to the family of Cyperaceae, Chenopodiaceae, Solanaceae, Leguminosae, Marsileaceae, Labiatae, Amaranthaceae and Asteraceae.Details of infested weed species are presented in Table 1.The hierarchy orders of five most widespread and abundant weed species of Agronomy Field Laboratory of BAU were Gnaphalium affine> Cyperusrotundus> Digitaria sanguinalis> Cynodon dactylon> Panicum repens.

Effect of cultivar, weeding regimes and their interaction on weed density and dry weight
Weed density was significantly influenced by different wheat cultivars.The highest weed density was recorded in BARI Gom-29 at 30 DAS (65.40 m -2 ), BARI Gom-28 at 60 DAS (70.33 m -2 ) and at 90 DAS (48.60 m -2 ).The lowest weed density was observed in BARI Gom-30 at 30 DAS (52.80 m -2 ), at 60 DAS (56.67 m -2 ) and at 90 DAS (34.13 m -2 ) (Table 2).Different weed management treatment exerted significant effect on weed density was at different days after sowing (Table 3).The highest weed density (81.11 m -2 , 94.56 m -2 and 49.11 m -2 , respectively) was observed in the treatment W 0 (no weeding) at 30 DAS, 60 DAS, 90 DAS.The lowest weed density (44.00 m -2 and 42.67 m -2 ) was recorded in the W 4 (use of pre emergence herbicide + one HW at 40 DAS) treatment at 30 DAS and at 60 DAS in W 2 (two HWs at 20 DAS and 40 DAS) and at 90 DAS (34.11 m - 2 ) in W 2 (use of straw mulch) treatment (Table 3).The probable reason for obtaining lowest weed population in use of pre emergence herbicide + and one HW at 40 DAS and in straw mulch treatments might be due to control of weed effectively in these two treatments.These results are in conformity with the observation made by Singh et al. (2010) who reported that application of pre-emergence herbicide followed by one hand weeding at 40 DAS reduced the weed population in wheat field.Weed density was significantly influenced by the interaction of different cultivars and weed management treatments (Table 4).The highest weed density (85.67 m -2 ) was obtained in V 1 W 0 (BARI Gom-28 × no weeding) at 30 DAS (112.00 m -2 ), in V 2 W 0 (BARI Gom-29 ×no weeding) at 60 DAS and (51.67 m - 2 ) in V 3 W 0 (BARI Gom-30 ×no weeding) at 90 DAS.The lowest weed density (30.33 m -2 ) was recorded in V 3 W 4 (BARI Gom-30 × use of pre emergence herbicide Panida + one HW at 40 DAS), at 30 DAS (33.67 m -2 ) in V 2 W 4 (BARI Gom 29 × use of pre emergence herbicide Panida + one HW at 40 DAS) at 60 DAS and (22.33 m -2 ) in V 3 W 2 (BARI Gom-30 × use of rice straw mulch) at 90 DAS (Table 4).
Effect of cultivar, weeding regimes and their interaction on yield and yield attributes of wheat Wheat cultivars did not show significant differences in all the plant characters measured at harvest except number of grains spike -1 , grain and straw yields.The number of grains spike -2 of wheat was significantly influenced by different cultivars.The highest number of grains spike -1 (34.63) was in BARI Gom-28.The lowest number of grains spike -1 (29.64) was found in BARI Gom-30 (Table 5).Significant variation in grain yield due to different cultivars was found in this experiment.The highest grain yield (3.44 t ha -1 ) was recorded in BARI Gom-29 and the lowest one (2.59 t ha -1 ) was observed in BARI Gom-28.Straw yield of wheat was also significantly influenced by the different cultivars.The highest straw yield (7.58 t ha -1 ) was obtained in BARI Gom-29 and the lowest one (5.30t ha -1 ) was obtained in BARI Gom-28 (Table 5).
Significant variation in grain yield was found due to different weeding treatments.The highest grain yield (3.29 t ha -1 ) was obtained in the treatment W 3 (use of pre emergence herbicide) which was statistically similar with the application of rice straw mulch.The use of preemergence herbicide Panida produced highest grain yield due to the fact that this treatment reduced weed crop competition and vigorous growth was happened and yield increased.Statistically similar yield was obtained from the application of rice straw mulch.Similar results were observed by De et al. (1983), Chen (1996) and Upadhyay and Tiwari (1996) who reported that application of pre-emergence herbicide produced the highest grain yield in wheat than hand weeding.The authors opined that plant absorbed soil moisture as vaporized forms but there was no enough facilities to vaporize the soil moisture in control treatment (no mulch) whereas, mulching treatments suppressed the weed growth and conserved available soil moisture and vaporized the moisture for absorption by the plants.It might have enhanced all the growth stages which directly or indirectly increased the yield of wheat.The lowest yield (2.60 t ha -1 ) was recorded from the treatment W 4 (use of pre emergence herbicide + one hand weeding at 40 DAS).The straw yield was influenced by different weeding treatments.The highest (7.27 t ha -1 ) straw yield was obtained in W 3 (Use of pre emergence herbicide) and the lowest straw yield (5.39 t ha -1 ) was in the treatment of W 0 (no weeding) (Table 6).Weed management treatments showed significant influence on harvest index.The highest value (33.57%) was in the treatment W 2 (Use of rice straw mulch).On the other hand, the lowest value was in the treatment W 4 (Use of pre emergence herbicide + one HW at 40) (29.62) (Table 6).W 0 = No weeding, W 1 = Two HW at 20 DAS and 40 DAS, W 2 = Use of rice straw mulch @ 6 t ha -1 , W 3 = Use of pre emergence herbicide Panida @ 1L ha -1 and W 4 = Use of pre emergence herbicide Panida @ 1L ha -1 + one HW at 40 DAS = Use of rice straw mulch @ 6 t ha -1 , W 3 = Use of pre emergence herbicide Panida @ 1L ha -1 and W 4 = Use of pre emergence herbicide Panida @ 1L ha -1 + one HW at 40 DAS, V 1 =BARI Gom-28, V 2 = BARI Gom-29 and V 3 = BARI Gom-30  ).NS = Not significant W 1 = Two HW at 20 DAS and 40 DAS, W 2 = Use of rice straw mulch @ 6 t ha -1 , W 3 = Use of pre emergence herbicide Panida @ 1L ha -1 and W 4 = Use of pre emergence herbicide Panida @ 1L ha -1 + one HW at 40 DAS Though plant height total tillers and effective tillers hill -1 were not significantly influenced by the interaction of cultivar and weed management practices but the number of grains spike -1 of wheat was significantly influenced by different cultivars and weed management treatment interactions.The highest number of grains spike -1 (37.42) was obtained in the interaction of V 1 W 3 (BARI Gom-28 × application of pre-emergence herbicide Panida) which was statistically identical with other interactions except V 3 W 1 interaction (BARI Gom-30 × two HW at 20 DAS and 40 DAS) in which the lowest number of grains spike -1 (21.52) was obtained (Table 7).The highest grain yield (4.36 t ha -1 ) was recorded in V 2 W 2 (BARI Gom-29 × use of straw mulch).This might be due to the fact that mulching treatments suppressed the weed growth and conserved available soil moisture and vaporized the moisture for absorption by the plants.
The lowest grain yield (2.21 t ha -1 ) was obtained in V 1 W 4 (BARI Gom-28 × use of pre emergence herbicide + one HW at 40 DAS) (Table 7).Straw yield of wheat was also significantly influenced by the interaction of cultivar and weed management treatment.The highest (8.99 t ha -1 ) straw yield was recorded in V 2 W 3 (BARI Gom-29 × use of pre emergence herbicide) and the lowest one (4.37 t ha -1 ) was observed in V 1 W 0 (BARI Gom-28 × no weeding) treatment (Table 7).Interaction between cultivar and weed management treatment showed significant influence on harvest index.The highest harvest index (39.91%)was recorded in V 1 W 0 (BARI Gom-28 × no weeding).On the other hand, the lowest value of harvest index (25.27%)was found in V 2 W 0 (BARI Gom-29 × no weeding) treatment (Table 7).From the results of the study it may be concluded that BARI Gom-29 with use of straw mulch or BARI Gom-29 with application pre-emergence herbicide Panida @ 1 L ha -1 might be used for obtaining higher yield as well as controlling weed in an effective manner.
But further studies are required in different regions of the country to confirm the present results.**=Significant at 1% level of probability, W 0 = No weeding, W 1 = Two HW at 20 DAS and 40 DAS, W 2 = Use of rice straw mulch @ 6 t ha -1 , W 3 = Use of pre emergence herbicide Panida @ 1L ha -1 and W 4 = Use of pre emergence herbicide Panida @ 1L ha -1 + one HW at 40 DAS, V 1 =BARI Gom-28, V 2 = BARI Gom-29 and V 3 = BARI Gom-30

Table 2 . Effect of cultivar on weed density and dry weight
*In a column, figures with the same letter(s) or without letter do not differ significantly whereas figures with dissimilar letter differ significant at 1% level of probability.

Table 4 . Interaction effect of cultivar and different weed management techniques on weed density and dry weight at different DATs
In a column, figures with the same letter (s) or without letter do not differ significantly whereas figures with dissimilar letter differ significantly (as per DMRT) **=Significant at 1% level of probability, W 0 = No weeding, W 1 = Two HW at 20 DAS and 40 DAS, W 2 *

Table 7 . Effect of interaction between cultivar and treatment on the yield and yield characters of wheat
In a column, figures with the same letter(s) or without letter do not differ significantly whereas figures with dissimilar letter differ significantly (as per DMRT). *