Experimental procedure and crop management Variety, seed rate, sowing time and seed treatment. Wheat variety BARI Gom 26, a popular variety among Bangladeshi farmers, was sown at 120 kg ha-1 in lines 20 cm apart on 5 December 2011 (Y1) and 28 November 2012 (Y2). To achieve excellent germination and protecting against fungal attack during the seedling stage, seeds were pre-treated with a fungicide (Provax-200 WP containing Carboxin and Thiram). To control soil-borne insects, Furadan 5G containing Carbofuran (systemic pesticide; FMC Corp., Philadelphia, PA, USA) was broadcast at 10 kg ha-1 during final land preparation. Fertilizer and irrigation. A blanket dose of P-K-S-B-Zn at 27-50-20-1-1.25 kg ha−1, recommended by the WRC, was applied as basal during final land preparation (Sarker et al., 2015). Basal N application was carried out as indicated for each treatment while top dressing was applied after the first irrigation at CRI and after the second irrigation at MT. Soil was irrigated four times at 21, 45, 75 and 85 DAS (Y1) and at 21, 45, 76 and 88 DAS (Y2).
Data collection:
The following data were recorded from an area of 0.5×0.4 m at 60 DAS in both years: initial plant population m−2 (PP) at 12 DAS, number of tillers m−2 (NT) at 40, 50 and 60 DAS, leaf area index (LAI) and above-ground dry matter (g m−2) (DM). Leaf area was calculated with an Automatic Leaf Area Meter (Model AAM-9, Hayashi Denko Co. Ltd., Tokyo, Japan) and the DM of above-ground parts was determined after drying in an oven at 70 °C for 72 h. CMRs were taken three times at 45, 55 and 65 DAS in both years with a Minolta SPAD-502. Readings were taken from 10 leaves from 10 independent plants plot-1, with three readings per leaf and then averaged. Yield and yield-contributing characters were recorded after harvesting the crop on 5 April 2012 and 1 April 2013. A yield sample was taken from a 2×4 m area (i.e., 10 middle rows) in 2011-12 and from a 3×2.8 m area (i.e., 14 middle rows) in 2012-13. Data on number of spikes m−2 (NS), spike length (SL), number of spikelets spike−1 (NSS), number of grains spike−1 (NGS), 1000-grain weight (TGW), GY and straw yield (SY) were recorded, the latter on a sun-dry basis for a large volume of straw. Data on GY and TGW were determined and adjusted to 12% moisture.
Data analysis:
Data on PP at 12 DAS, NT at 40, 50 and 60 DAS, LAI, DM, CMRs at 45, 55 and 65 DAS, NS, SL, NSS, NGS, TGW, GY and SY were analysed by partitioning the total variance and treatment means were compared with the help of R package ‘stats’ (version 2.15.3) “R” at the 5% level of significance (R Core Team, 2013). Correlation analysis between GY and SPAD values at different DAS in both years was conducted by STAR (Statistical Tool for Agricultural Research; IRRI, 2014).