COMPETITIVE EFFECT OF FREE FLOATING PLANTS ON WEED CONTROL, GROWTH AND YIELD OF TRANSPLANTED AMAN RICE

Abstract

A study was conducted to find out the suppressing ability of floating weeds in T. aman rice (Oryza sativa L.) at the Agronomy field of Sher-e-Bangla Agricultural University, Dhaka, Bangladesh from July 2019 to December 2019. The experiment consisted of two factors viz. rice varieties (3) i.e. Tulshimala, BR11(Mukta) and BRRI hybrid dhan6, and weed management (4) i.e. weedy check (control), Integrated Weed Management (one pre-emergence herbicide Pretilachlor 6% + pyrazosulfuron 0.15% and one hand weeding), spreading of Water Lettuce (Pistia stratiotes), Duckweed (Lemna minor) and Kariba weed (Salvinia molesta) in 0.5 m ii

2 area. The experiment was laid out in a split-plot design with three replications. The ranking of the relative rate of spreading (RRS) over the experiment L. minor > S. molesta > P. stratiotes. A total of 6 weed species representing 5 families were found from the transplanting to the later stage of rice growth where the occurrence of weed infestation related to rice variety and crop growth. BRRI hybrid dhan6 significantly suppressed weeds in related plots. Integrated weed management successfully control all weeds and gave the highest weed control efficiency and weed control index. Although weed biomass significantly reduced, the morphological and biomass characteristics of T. aman rice varieties got disadvantages when grown with P. stratiotes and S. molesta. Cultivation of BRRI hybrid dhan6 along with weed control through integrated weed management gave the highest grain yield (5.92 t ha -1 ) and the highest economic return comparable to other treatment combinations. However, the spreading of L. minor facilitated optimal weed control and good yields were harvested without significant differences and as well as net return irrespective of varieties. Therefore, weed competitive variety should be considered along with the spreading of L. minor to reduce herbicide loads in the environment and to the evolution of cross-resistant weed populations.