Roy, D. K.Nandan, Neha2018-02-062018-02-062017http://krishikosh.egranth.ac.in/handle/1/5810040482A field experiment was undertaken during kharif of the year 2016 at the Research Farm of Dr. Rajendra Prasad Central Agricultural University, Pusa (Samastipur), Bihar to study the “Effect of weed management and nitrogen on weed dynamics and yield of rice under aerobic condition”. The experiment was conducted in split plot design having three levels of nitrogen in main plots (N1-120 kg N/ha, N2-140 kg N/ha and N3-160 kg N/ha,) and six weed management practices (W1- Pyrazosulfuron @ 25 g/ha (20 DAS), W2-Bispyribac sodium @ 25 g/ha (20 DAS), W3-Pyrazosulfuron @ 25g/ha + Bispyribac sodium @ 25g/ha (20 DAS), W4-Pendimethalin @ 1000g/ha (PE)+ W3 (20 DAS), W5-Weed free (2 Hand weeding at 20 & 40 DAS) and W6-Weedy check ) in sub plots, replicated thrice with Abhishek as the test variety. Higher level of nitrogen i.e. 160 kg/ha exhibited better expression in respect of growth and yield attributes than the other two levels and it was somehow also comparable to 140 kg N/ha in terms of yield attributes specially. The better performance in terms of growth and yield attributes were also further reflected correspondingly in grain and straw yields. The harvest index however did not show significant variation due to nitrogen treatments. All the weed management practices either herbicidal or manual weeding had profound effect on growth and yield attributes as well as the ultimate yield as reflected in their superiority over the weedy check. Amongst the three post-emergence applications of herbicides either alone or in combinations, combination of two herbicides i.e. Pyrazosulfuron @ 25 g/ha + Bispyribac sodium @ 25 g/ha (W3) was superior to their alone applications (W1& W2), which in turn performed better than these two. However, when these two post-emergence herbicidal combination were supplemented with pre-emergence application of Pendimethalin @ 1000 g/ha recorded top spot in almost all the growth and yield characters and also in the yields of grain and straw except 2 hand weeding (W5). However, the pre and post-emergence herbicidal combinations (W4) and the treatment of two hand weeding did not differ significantly in these respects. The results pertaining to weed population, weed dry weight and nutrient uptake by crop separately were a close reflection of growth and yield pattern whereas nitrogen level of 160 kg/ha scored over the other two nitrogen doses in main plots and the pre and post-emergence applications of Pendimethalin @ 1000 g/ha + Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha established its superiority over the rest of the herbicidal treatments except in weed free condition wherein all these characters were superior in sub plots. Weed control efficiency of 2 hand weeding (70.81%) was superior to Pendimethalin @ 1000 g/ha + Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha (66.13%), Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha (59.83%), Bispyribac sodium @ 25 g/ha (51.48%) and Pyrazosulfuron @ 25 g/ha (40.40%). N, P and K content in grain and straw also followed the similar trend as above in all the treatments except the weedy check in which it was significantly lower. The most glaring part of the results rested in its economic studies, wherein treatment with 160 kg N/ha fetched higher gross return, net return and finally the B: C ratio than other two while all the herbicidal treatments either post emergence applications alone or combination of pre and post-emergence applications fetched higher net return and scored better B: C ratio than the two hand weeding. Pendimethalin @ 1000 g/ha + Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha (₹34,338/ha) cornered the highest net return closely followed by Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha (₹34,059/ha) and the later was also statistically close to Bispyribac sodium @ 25 g/ha alone (₹32,446/ha). The B: C ratio further widened the gap between manual weeding and herbicidal applications. The highest B: C ratio of 1.28 was recorded from Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha followed in descending order by Bispyribac sodium @ 25 g/ha alone (1.26) and Pendimethalin @ 1000 g/ha + Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha (1.21). Two hand weeding had a B:C ratio of only 0.59 which was next only to the weedy check (0.58). Thus it may be summed up that the nitrogen level of 160 kg/ha is superior to 140 kg N/ha and 120 kg N/ha. Secondly, high cost involved in manual weeding makes herbicidal treatments more viable proposition. Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha, Bispyribac sodium @ 25 g/ha alone and Pendimethalin @ 1000 g/ha + Bispyribac sodium @ 25 g/ha + Pyrazosulfuron @ 25 g/ha are three most effective herbicidal combination treatments in direct seeded rice under aerobic condition.ennullThesis