2.1. Experimental Site and Season A two-year crop sequence (Rice-Wheat-Mungbean) experiment was conducted on a farmers' field located at Durbachara village of Bhangnamari union, situated at Gouripur sub-district in Mymensingh district of Bangladesh. Wheat was grown during mid November-March in 2014-15 and 2015-16 in the cool dry season. The site was located at latitude 24.75o N and longitude 90.50o E) at 18 m altitude.
2.2. Edaphic and Climatic Condition The experiment site is situated on the Old Brahmaputra Floodplain of predominantly dark grey non-calcareous alluvium soils under the Sonatala series. It was on flood free medium-high land. During the study period, March was the warmest month when the highest maximum temperatures were 30.6 and 31.06 o and the highest minimum temperatures were 18.4 and 20.2 o in 2014-15 and 2015-16, respectively followed by February. Temperature declined gradually from November to January. January was the coldest month. November in 2014, and Dcember and March in both years were the driest months when no rainfall was recorded.
The highest rainfall event comprising about 20 mm was recorded in February during both years. November and March enjoyed the highest sunshine hours while the December had least sunshine hours during both years.
2.3. Experimental Treatments and Design The present study deals with wheat cv. BARI Wheat 26 in two consecutive years on the same plots with treatments comprising a combination of six tillage and weed control practices viz. (i) Conventional tillage (CT)+3 hand weeding (HW) (Control); (ii) Glyphosate (Gly)+strip planting (SP)+1HW; (iii) Gly+SP+pre-emergence (PE) herbicide, (iv) Gly+SP+post-emergence (PO) herbicide), (v) Gly+SP+PE+PO, and (vi) Gly+SP+weed-free (WF); and two levels of rice straw as (i) R0: no-residue and (ii) R50: 50% residue. Treatments were arranged in randomized complete block design, replicated three times, with plots split for residue levels.
2.4. Tillage Operation In each 9 m × 5 m plot, conventional tillage (CT) was done using a two-wheel tractor (2WT). The land was prepared by four plowings and cross plowing followed by sun-drying for two days and levelling. Strip planting (SP) was done by a Versatile Multi-crop Planter (VMP) in a single pass operation. Strips had prepared for 4 rows, each 6 cm wide and 5 cm deep. Three days before SP operation, glyphosate had applied @ 3.7 L ha-1.
2.5. Seed Sowing In CT, seeds were sown manually in rows 20 cm apart. In SP, continuous line sowing was done using the VMP at 20 cm apart. Seeds were covered with soil just after sowing. In both CT and SP, 120 kg seeds ha-1 were sown on November 20 in both years.
2.6. Residue Retention Practice Two levels of straw residues of monsoon rice were used in this study. In no-residue practice, seeding was done without retaining rice straw while in 50% residue practice, 50% residue (height basis) of previously harvested rice was used. This amount of residue was spread over the plots after seeding of wheat seeds.
2.7. Weed Control Practices In CT, 3 HWs were done at 25, 45, and 65 DAS. In SP, 1 HW was done at 25 DAS. In the weed-free (WF) treatment, six HWs were done at 15, 25, 45, 65, 75, and 90 DAS. Herbicides were applied by hand-operated knapsack sprayer fitted with a flat-fan nozzle at a spray volume of 300 L ha-1. Herbicides used in different treatments are presented in Table 2
2.8. Cultural Operations The nitrogen in the form of urea, phosphorus from triple super phosphate, potassium from muriate of potash and sulfur from gypsum was applied @ 100, 26, 33, and 20 kg ha-1, respectively. The entire amount of PKS was broadcast before seeding and residue retention. Two-thirds of the N was applied at final ploughing and one-third at crown root initiation (CRI) stage. Irrigations were applied at 20, 55 and 80 DAS. First and third irrigation was very light and excess water was drained out to prevent wilt and lodging. Cutworm was controlled by Tricosale® 20EC @ 500 ml ha-1. Bipolaris leaf blight was controlled by Tilt® 250 EC @ 0.5 ml L-1 of water. Bird was kept away for 10 DAS and rat was controlled using zinc phosphide poison.
2.9. Data Recording Weed densities (plants m-2 ) were recorded in a 0.50 m × 0.50 m quadrat at 25, 45 and 65 DAS, and at crop harvest. The quadrat was placed randomly at four places in each plot. The weed density was counted in plants m-2, and the weed biomass was recorded in g m-2 after oven drying the samples at 70o for 72 hrs. The similarity among weed species between CT and SP in two consecutive years was calculated using the following formula.