Effect of weed management practices on the performance of transplanted aman rice varieties

A field experiment was carried out to study the effect of weed management practices on the performance of transplanted aman rice varieties. The experimental treatments comprised three varieties viz. BR11, BRRI dhan39 and Binadhan7 and seven weeding treatments viz., weedy check, hand weeding at 15 and 35 DATs, application of early post-emergence herbicide Manage (Pyrazosulfuron ethyl), application of pre-emergence herbicide Rifit (Pretilachlor), Manage + one hand weeding at 35 DAT, application of Rifit + one hand weeding at 35 DAT and weed free. The experiment was laid out in a randomized complete block design with three replications. The results reveal that varieties should significant variation on plant height, number of total tillers hill -1 , number of effective tillers hill -1 , number of non-effective tillers hill -1 , panicle length, number of grains panicle -1 , number of sterile spikelets penicle -1 , 1000-grain weight, grain yield, straw yield and harvest index. Grain yield was the highest in BRRI dhan39. Weeding regime had also significant effect on all the studied crop parameters except 1000-grain weight. The highest grain yield was obtained from weed free condition followed by hand weeding at 15 and 35 DATs. Interaction between variety and weeding regime had significant influence on all the studied crop parameters except 1000-grain weight. The highest grain yield was obtained from the interaction of BRRI dhan39 × weed free condition which was statistically identical (5.50 t ha -1 ) with interaction of variety BR11 × two hand weedings at 15 and 35 DATs. Therefore it may be concluded that BR11 rice could be cultivated using two hand weedings at 15 and 35 DATs for obtaining higher yield.

Binadhan7 and seven weeding treatments viz., weedy check, hand weeding at 15 and 35 DATs, application of early post-emergence herbicide Manage (Pyrazosulfuron ethyl), application of pre-emergence herbicide Rifit (Pretilachlor), Manage + one hand weeding at 35 DAT, application of Rifit + one hand weeding at 35 DAT and weed free.The experiment was laid out in a randomized complete block design with three replications.The results reveal that varieties should significant variation on plant height, number of total tillers hill , number of sterile spikelets penicle -1 , 1000-grain weight, grain yield, straw yield and harvest index.Grain yield was the highest in BRRI dhan39.Weeding regime had also significant effect on all the studied crop parameters except 1000-grain weight.The highest grain yield was obtained from weed free condition followed by hand weeding at 15 and 35 DATs.Interaction between variety and weeding regime had significant influence on all the studied crop parameters except 1000-grain weight.The highest grain yield was obtained from the interaction of BRRI dhan39 × weed free condition which was statistically identical (5.50 t ha

Introduction
In Bangladesh about 75.61% of the total cropped area and over 80% of the total irrigated area are planted rice (BBS, 2013).Food shortage was one of the major problems here due to over population and low yield of food crops.To reach the goal, it was necessary either to increase the crop area or to increase yield unit -1 area.But due to high population pressure, horizontal expansion of land was not possible.So, increasing yield unit -1 was the only means.In Bangladesh, agriculture is characterized by rice based cropping systems.Rice is extensively grown here in aus, aman, and Boro seasons.Variety itself is a genetic factor which contributes a lot in producing yield components and yield of a particular crop.Yield components such as number of effective tillers hill -1 , number of grains panicle -1 and weight of individual grain contribute to increase or decrease the yield.Weeds are the major source of yield loss in upland rice and its control is labor intensive.The climate as well as the edaphic condition of Bangladesh is favorable for the growth of weeds.So, the rice crop is usually infested heavily with weeds resulting in grain yield reduction by 70-80% for direct seeded aus rice, 30-40% for transplanted aman rice and 22-36% for modern boro rice varieties (Mamun, 1990;BRRI, 2008).Weeds compete with crops for nutrients, space and water and thus reduce crop yield.Weeds also exert allelopathic effect on the growth of rice plant (Ismail and Siddique, 2010).Weeding has a great influence on the performance of the associated crop.Salam et al. (2014) obtained higher yield of boro rice using a pre-emergence herbicide + one hand weeding at 35 DAT.Thus the best weeding needs to be adopted by the farmers with a view to reducing weed infestation and maximizing rice yield.Proper weed management ensures higher yield.Weeding keeps the land clean and soil becomes well aerated and this facilitates the absorption of more nutrients, moisture and higher reception of solar radiation for better growth and yield of rice.The present study was therefore, undertaken to observe the effect of variety, different weeding regimes and interaction effects of variety and different weeding regimes on the performance of transplanted aman rice.

Materials and Methods
The experiment was conducted at the Agronomy Field Laboratory of Bangladesh Agricultural University, Mymensingh during the period from June to December 2013 to study the effect of weed management practices on the performance of transplanted aman rice varieties.The experimental area is characterized by non-calcareous dark grey floodplain soil belonging to the Sonatala Soil Series under the Old Brahmaputra Floodplain, Agro-Ecological Zone 9 (UNDP and FAO, 1988).The experimental field was medium high land having silty loam soil with pH 6.8.The experiment included two factors, three varieties viz V 1 (BR11), V 2 (BRRI dhan39) and V 3 (Binadhan-7) and seven weeding treatments viz.W 1 (weedy check), W 2 (hand weeding at 15 and 35 DATs), W 3 (application of early post-emergence herbicide Manage (1 L/ha), W 4 (application of pre-emergence herbicide Rifit (185 g/ha)), W 5 (application of manage + one hand weeding at 35 DAT), W 6 application of Rifit + one hand weeding at 35 DAT) and W 7 (weed free).The experiment was laid out in a randomized complete block design (RCBD) with three replications.Total number of unit plots was 3×7×3=63 and each plot size was 4.0 m × 2.5 m.The distance maintained between the individual unit plots was 0.5 m and that between the replications was 1.0 m.The sprouted seeds were sown in the nursery bed on 15 June 2013.The land was thoroughly prepared with the help of country plough and ladder and was uniformly fertilized with urea, triple superphosphate, muriate of potash, gypsum and zinc sulphate @ 200, 115, 125, 100 and 12 kg ha -1 , respectively (BRRI, 2011).All the fertilizers were applied at the time of final land preparation but urea was applied at three equal splits at 15, 30 and 45 DATs.The layout of the field was made after final land preparation.The seedlings were uprooted on 16 July 2013 and they were immediately transferred to the main field.Rice was transplanted on 16 July 2013.The intercultural operations were done whenever it necessary.When 90% of the spikelets become golden yellow in color the crops were harvested.BRRI dhan39 and Binadhan7 were harvested on 20 November and BR11 was harvested on 11 December 2013.The harvested crop of each plot was separately bundled, properly tagged and then brought to (21 days earlier than that of variety BR11) threshing floor.The grains were cleaned and sun dried and straws were also sun dried properly.Finally grains and straw yields plot -1 were recorded and converted to t ha -1 . The recorded data were compiled and tabulated for statistical analysis.Analysis of variance was done with the help of computer package, MSTAT.The mean differences among the treatments were adjudged by Duncan's Multiple Range Test (Gomez and Gomez, 1984).

Results and Discussion
Effect of variety on yield and yield components of transplanted aman rice Varieties of transplanted aman rice should significant variation on plant height, number of total tillers hill , 1000-grain weight, grain yield, straw yield and harvest index (Table 1).Variety BR11 produced the tallest plants (107.90 cm) while Binadhan-7 produced the shortest plants (91.70 cm).Binadhan-7 produced the highest number (8.77) of total tillers and effective tillers hill -1 (6.17) and number of effective tillers hill ) with that of variety BR11 and the lowest grain yield (4.52 t ha -1 ) was obtained in Binadhan-7.This variation in grain yield might be due the characteristics of the cultivars.These results are in conformity with that obtained by Siddeque et al. (2002) and BRRI (1995) who reported the differences of grain yield due to varieties.
The highest straw yield (5.25 t ha -1 ) was found in BR11 and the lowest straw yield (4.24 t ha -1 ) was found in Binadhan-7 which was statistically identical with BRRI dhan39.The highest harvest index (54.78%)was found in Binadhan-7 which was statistically similar with BRRI dhan39 and the lowest one (46.86%)was found in BR11.It was reported that variety had a great influence on harvest index (Tyeb et al., 2013).(5.49) was obtained from W 0 (No weeding) treatment.The highest number of non-effective tillers hill-1 (3.38) was produced by W 0 (No weeding) treatment, while the lowest number of non-effective tillers hill -1 (2.22) was produced by W 3 (Application of preemergence herbicide Rifit) treatment.The longest panicle (24.36 cm) was observed in W 2 (Application early post-emergence herbicide Manage) treatment which was statistically identical with that of W 1 (Two hand weedings at 15 and 35 DATs) and the shortest one (20.55cm) was observed in W 0 (No weeding) treatment.The highest number of grains panicle -1 (110.4) was produced by W 6 (Weed free) treatment which was statistically identical with W 4 (Application of Manage + one hand weeding at 35 DAT) and the lowest number of grains panicle -1 (80.41) was produced by W 0 (No weeding) treatment.In this study weed free treatment produced the highest number of grains panicle -1 which might be attributed due to vigorous growth of rice plant without crop-weed competition in this treatment.The highest number of sterile spikelet's panicle -1 (22.55) was produced by W 0 (No weeding) treatment, while the lowest one (15.16)was produced by W 6 (weed free) treatment.The highest grain yield (5.05 t ha -1 ) was produced by W 6 (Weed free) treatment which was statistically identical with W 1 (Hand weeding at 15 and 35 DATs) treatment, while the lowest grain yield (3.72 t ha -1 ) was produced by W 0 (No weeding) treatment.Under weed free condition, plants got maximum nutrients, light and water, which resulted in maximum grain yield.The highest straw yield (5.56 t ha -1 ) was observed in W 6 (Weed free) treatment and the lowest one (4.11t ha -1 ) was observed in W 3 (Application of pre-emergence herbicide Rifit) treatment which was statistically identical with W 0 (No weeding).The highest harvest index (52.12%)was observed in W 2 (Application of early post-emergence herbicide Manage) treatment which was statistically identical to W 3 (Application of pre-emergence herbicide Rifit) and W 5 (Rifit + one hand weeding at 35 DAT).The lowest straw yield (4.11t ha -1 ), and the lowest harvest index (47.22%)were found from W 0 (No weeding) treatment.The interaction of variety and weeding regime had significant effect on all the yield and yield components except 1000-grain weight (Table 3).The tallest plant (111.9 cm) was found in BR11 under Manage + one hand weeding at 35 DAT (V 1 × W 4 ) treatment and the shortest one from Binadhan7 under no weeding (V 3 × W 0 ) treatment among the interactions.The highest number of total tillers hill -1 (11.13) was observed in Binadhan-7 under weed free (V 3 × W 6 ) treatment and the lowest one (5.13) in BR11 under no weeding (V 1 × W 0 ) treatment.The highest number of effective tillers hill -1 (7.33) was found in Binadhan-7 under weed free (V 3 × W 6 ) treatment.The lowest number of effective tillers hill -1 (4.33) was found in variety BR11 under no weeding (V 1 × W 0 ) treatment which was followed by BRRI dhan39 in no weeding (V 2 ×W 0 ) treatment.The highest number of non-effective tillers hill -1 (3.63) was produced by variety BR11 and Binadhan-7 in W 0 (No weeding) treatment and the lowest one (1.93) was observed in the variety BR11 with W 6 (Weed free) and variety BRRI dhan39 with W 3 (Pre-emergence herbicide Rifit).The longest panicle (25.50 cm) was found in BRRI dhan39 under Rifit + one hand weeding at 35 DAT (V 2 × W 5 ) treatment and the shortest panicle (18.84 cm) was found in Binadhan7 under no weeding (V 3 × W 0 ) treatment.The highest number of grains panicle -1 (128.0) was produced in BRRI dhan39 under Manage + one hand weeding at 35 DAT (V 2 × W 4 ) treatment and the lowest one (72.16)was produced by Binadhan-7 under no weeding (V 3 ×W 0 ) treatment which was statistically identical with V 3 × W 2 treatments.The highest number (29.23) of sterile spikelet's panicle -1 was found in Binadhan-7 under no weeding (V 3 ×W 0 ) treatment and the lowest one (12.65)was found from BRRI dhan39 with weed free (V 2 × W 6 ) which was statistically identical with (V 2 × W 3 ) treatment.The highest grain yield was recorded from variety BRRI dhan39 × weed free treatment (V 2 × W 6 ) treatment which was statistically similar (5.50 t ha -1 ) with variety BR11 × two hand weedings at 15 and 35 DATs (V 1 × W 1 ) treatment, BRRI dhan39 × two hand weedings at 15 and 35 DATs and BR11 × weed free treatment.The lowest grain yield was obtained from BR11under no weeding treatment which was statistically similar with BRRI dhan39 × no weeding and Binadhan-7 × no weeding treatments.The highest straw yield (6.17 t ha -1 ) was found in BR 11 under weed free treatment (V 1 × W 6 ) which was statistically identical with V 1 × W 5 treatment.The lowest straw yield (3.83 t ha -1 ) was produced by BRRI dhan39 under no weeding (V 2 × W 0 ) and V 3 × W 3 , V 3 × W 4 and V 3 × W 5 treatments.The highest harvest index (56.19%)was observed in BRRI dhan39 × application of pre-emergence herbicide Rifit + one hand weeding at 35 DAT (V 2 × W 5 ) treatment which was statistically identical with (V 3 × W 4 ) treatment.The lowest harvest index (42.86%)was observed in BR11 under Rifit + one hand weeding at 35 DAT (V 1 × W 5 ) treatments.From the results of the study it may be concluded that BR11 rice could be cultivated using two hand weedings at 15 and 35 DATs for obtaining higher yield.

Conclusion
From the results of the study it may be concluded that among the different treatment combinations, BR11 rice with two hand weedings at 15 and 35 DATs might be done for controlling weed effetely and for obtaining higher yield of transplanted aman rice.

Table 1 .
Effect of variety on the yield and yield components of transplanted aman rice In a column figures with same letters or without letters do not differ significantly whereas figures with dissimilar letter differ significantly as per DMRT.
** = Significant at 1% level of probability Effect of weeding regime on yield and yield components of transplanted aman rice All the yield and yield contributing characters except 1000-grain weight were significantly influenced by weeding regimes (Table2).The tallest plant (103.3 cm) was found in W 4 (herbicide Manage + one hand weeding at 35 DAT) treatment which was statistically identical with W 1 (Two hand weedings at 15 and 35 DATs), W 2 (Application of early post-emergence herbicide Manage), W 3 (Pre-emergence herbicide Rifit), W 5 (Rifit + one hand weeding at 35 DAT) and W 6 (Weed free) treatments.The shortest plant (90.20 cm) was found in W 0 (No weeding) treatment.Weed competition was severe in no weeding condition and thus plant height of rice was reduced.The highest number of total tillers hill-

Table 2 .
Effect of weeding regime on the yield and yield components of transplanted aman rice

Table 3 .
Interaction effect of variety and weeding regime on the yield and yield components of transplanted aman rice