Effect of irrigation schedule, weed management and nitrogen levels on weed growth in rice (Oryza sativa) under aerobic conditions

A field study was conducted at Agricultural Research Station, Kampasagar, Nalgonda district of Andhra Pradesh during the kharif seasons of 2008 and 2009 to find out the effect of irrigation schedules, weed management practices and nitrogen levels on weed growth, nutrient depletion and yield of aerobic rice. The major weed flora observed in the experimental plot was Echinochloa colona L., Cynodon dactylon Pers., Dactyloctenium aegyptium Beauv., Cyperus rotundus L. (Monocots), Eclipta alba Hassk., Trianthemaportulacastrum L. and Amaranthus viridis L. (Dicots) during both the years. Irrigation scheduled at seven days interval during vegetative stage and four days interval during reproductive stage resulted in significantly higher weed density, weed dry matter production and NPK removal by weeds and higher panicle number and weight, filled spikelets per panicle grain yield and NPK uptake at harvest than that of irrigation scheduled once in two days. Pre-emergence application of pendimethalin @ 1 kg/ha fb cono weeding at 30 DAS and one HW at 45 DAS recorded significantly lower weed density, weed dry matter production and NPK uptake by weeds and significantly higher panicle number and weight, filled spikelets per panicle, NPK uptake at harvest and grain yield than that of pre-emergence application of pendimethalin @ 1 kg/ha fb 2, 4-D Na salt @ 1 kg/ha at 40 DAS and HW at 20 and 45 DAS. Among latter treatments, significantly lower values of above said weed parameters and significantly higher crop parameters were observed with pre-emergence application of pendimethalin @ 1 kg/ha fb 2, 4-D Na salt @ 1 kg/ha at 40 DAS as compared to HW at 20 and 45 DAS. Weed density, weed dry matter production and NPK removal by weeds and panicle number, length and weight, filled spikelets per panicle, grain yield and NPK uptake at harvest were significantly higher at 180 kg N/ha during both the years.