The deployment of weed competitive variety is not only ecofriendly but also a very cost effective tool for integrated weed management. Considering the high vulnerability of aerobic rice to weeds, development of weed competitive aerobic rice variety has been suggested by many researchers .No work has so far been done to assess the ability of the huge pool of Bangladeshirice germplasms to wrestle weeds under aerobic soil conditions. In this backdrop, the present study was undertaken to study the variation in weed competitiveness among selected high yielding rice varieties and to recognize agronomic traits conferring weed competitiveness of rice grown under aerobic soil conditions.Maximum weed growth was observed in weed monoculture. In terms of weed rating BRRI dhan59, BRRIdhan67 and Binadhan-10 appeared as the most weeds suppressive since weed ratings against these variety were low. Weed growth was rated between 4 and 5 for BRRI dhan50, BRRI dhan58, BRRI hybrid dhan3, Binadhan-6 and Agrodhan-14,hydroponic fodder system and between 5 and 6 for BRRI dhan28, BRRI dhan29 and BRRI dhan47 indicating moderate weed suppressive .
Weed rating in BRRI dhan55 and Binadhan-8 and highest weed rating > 7 in Binadhan-5signify poor competitiveness against weeds. Weed dry matter followed almost similar trend as visual weed rating. Mean weed pressure across variety was 37.83 g m−2 against 92.32 g m−2 recorded in weed monoculture, which denotes that on average, rice variety reduced weed pressure by about 59%. BRRI dhan59emerged as the most weed suppressive variety reducing weed pressure by 79%followed by BRRI dhan67 and Binadhan-10. Highest weed pressure of 62.8 g m−2 was found in Binadhan-5 which was 32%less than in weed monoculture. Other varieties were intermediate in suppressing weeds within the range of 41 to 79%. Maximum weed density of 197 m−2 was recorded in weed monoculture. The rice variety did not significantly differ with respect to weed density, which was within a narrow range from 69 to 114 m−2. The average weed density across variety was 94 m−2 which was 52%less compared to the weed monoculture. Relative chlorophyll content was not significantly influenced by variety .
Numerically, the highest chlorophyll content was observed in BRRI dhan55 and the lowest chlorophyll content was observed in BRRI dhan67 .Higher SPAD values indicate greener and healthier plants. Relative chlorophyll content was significantly affected by weeding regimes aeroponic tower garden system. In weed free condition higher chlorophyll value was found and in weedy treatment lower chlorophyll content was found. Weed competition was severe in weedy condition and thus lowest chlorophyll was produced. On the other hand,in weed free treatment throughout the crop growth period, higher chlorophyll value was produced . SPAD value was higher in weed-free condition than in weedy condition. SPAD values were greatly reduced by weed interference and this was reflected in yield performance. 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 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, 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.