Water - weed interactions in aerobic rice

Abstract

A field study was undertaken at Agronomic Research Station, Chalakudy, Kerala for developing suitable water and weed management strategies for aerobic rice. The trial was laid out with three levels of irrigation in the main plot [irrigation at 10, 20 and 30 mm CPE (cumulative pan evaporation)] and five weed management treatments in the subplot (pre emergent herbicide oxadiargyl followed by hand weeding, 2,4- D sodium salt or bispyribac sodium at 20 days after sowing (DAS), hand weeding at 20 and 40 DAS and unweeded control). Irrigation at 10 mm CPE increased crop growth, but reduced weed growth. Less irrigation (30 mm CPE) favoured the growth and density of grasses and broad leaf weeds and produced the highest weed dry matter. Sedge population was more in frequently irrigated plot (10 mm CPE). Moisture stress in 30 mm CPE resulted in 44 per cent yield loss. Weed competition caused 64 per cent yield reduction. Both water and weeds together accounted for 85 per cent yield reduction. Irrigation at 10 mm CPE recorded the highest grain yield and weed control efficiency, but lowest water productivity. Among weed management practices, hand weeding at 20 and 40 DAS recorded the highest grain yield, weed control efficiency and water productivity. However, application of oxadiargyl followed by bispyribac sodium resulted in better water productivity and recorded highest B:C ratio.