The experiment was carried out at the Agronomy Field Laboratory and Weed Management Laboratory, Department of Agronomy, Bangladesh Agricultural University, Mymensingh during the period from February to June 2016. Geographically the experimental area is located at 24˚75’N latitude and 90˚50’E longitudes at the elevation of 18 m above the sea level. The experimental field was medium high land belonging to the Sonatola Soil Series of Grey Floodplain soil under the agro-ecological zone of Old Brahmaputra Floodplain.The region occupies the large area of Brahmaputra sediments which were laid down before the river shifted into its present Jamuna Channel about 200 years ago . The soil of the experimental field was more or less neutral in reaction with pH value 6.8, low in organic matter content and bulk density . The land type was medium high with silty-loam in texture . Soil contained 0.11% total N, 50.40 ppm available P, 7.36ppm available S, 0.16 me% exchangeable K.
The varieties from diverse genetic sources and origins demonstrated a broad range in phonological parameters. Growth duration of the varieties in this study ranged from 117 to 143 days. Average flowering period was 109 days in weed free and 107 days in weedy condition. Average growth duration was 134and 132 days in weed free and weedy condition, respectively. BRRI dhan28 and BRRI dhan55 took less than 100 days for flowering and near about 120 days for maturing in both conditions. BRRI dhan67, BRRI dhan47 and BRRI dhan58 commenced flowering between 100 and 105 DAS and consequently matured by125-130 days in weed free condition and matured 2-3 days early in weedy condition.BRRI dhan29 required the longest duration of more than 115 days to initiate flowering and matured after 140 days. The variety and weeding regime exhibited significant differences in plant height at most of the sampling dates, however, cannabis grow tray their interaction had no significant effect. At 15 DAS plant height ranged from 7.65 to 11.55cm. Here, highest plant height at 15 DAS was produced by BRRI dhan59, followed by Binadhan-10 and the lowest plant height was obtained from Binadhan-5 followed by Binadhan-8.
At 30 DAS, plant height ranged from 13.05 to 18.55 cm. Here, BRRI dhan59 was the tallest variety and Binadnan-5 was the shortest one which was at par with BRRI dhan47, BRRI dhan55, Binadhan-8 and BRRI hybriddhan3. At 45 DAS, values are not significant. Both at 60 and 75 DAS, Agrodhan-14 was the tallest cultivar which was followed by BRRI hybrid dhan3, and BRRI dhan28 was the shortest one which was at par with BRRI dhan59 and BRRI dhan50. At harvest, plant height ranged from 74.4 to 91.97 cm. Agrodhan-14 appeared as the tallest variety which was at par with Binadhan-6, and BRRIdhan50 was the shortest variety which was closely followed by BRRI dhan58.Weed infestation reduced plant height at all growth stages. The magnitude of reduction varied with growth phase, and reduction in plant height in weedy treatments followed a declining trend with advancement of crop growth. Presence of weeds markedly decreased plant height by 3, 16, 14, 3.5, 3.5 and 10% at15, 30, 45, 60, 75 DAS and harvesting time, respectively. In case of interaction,the tallest variety was Binadhan-6which was followed by Agrodhan-14 in weed free condition at 60 DAS. The shortest variety was Binadhan-10 which was statistically similar with BRRI dhan50 in weedy condition and BRRI dhan28 and BRRI dhan59 in weed free condition . Relative yield loss is an excellent indicator of weed tolerance of a variety. Lower the relative yield loss, higher the degree of weed tolerance, since weed tolerance refers to the ability to maintain high yield in the presence of weed competition.
The rice varieties showed wide diversity in relative yield loss, which ranged from 43.4% to 82.1%.The relative yield loss was lowest in BRRI dhan 59, followed by BRRI dhan 67 and Binadhan-10 which exhibited high weed tolerance. Regression study showed that weed dry weight was strongly and negatively correlated with early plant height and early visual vigor and highly correlated with above ground crop biomass and grain yield .Plant height beyond 30 DAS maintained a weak negative correlation with weed dry weight . As expected, weed rating was strongly and positively correlated with weed dry weight, but negatively correlated with early plant height, early visual vigor and grain yield. Grain yield showed a very strong positive correlation with above ground crop biomass and highly positive correlation with early plant height.While percent filled grains had maximum predictive power for grain yield. Weed biomass could explain rain yield by 83%and relative yield loss by 95%.The cultivars evaluated in this study varied not only in yield and weed suppressing ability, but also in all the agronomic traits measured.