Pathania, PawanSingh, Gurpreet2018-09-122018-09-122018-07-20http://krishikosh.egranth.ac.in/handle/1/5810072835The present study was carried out in a continuing experiment at the Bhadiarkhar farm of the university. Eight cropping systems [C1- „rice – wheat‟, C2- „rice – pea – summer squash‟, C3- „okra – radish – onion‟, C4- „turmeric – pea – summer squash‟, C5- „rice – lettuce – potato‟, C6- „rice – palak – cucumber‟, C7- „rice – broccoli – radish‟, C8- „colocasia – pea + coriander‟] were evaluated during 2016-17 in RBD with four replications for their effect on weed menace, production potential, economic feasibility, energy relations and yield and nutrient losses due to weeds under mid hill conditions of Himachal Pradesh. There were 24 weed species which invaded different cropping systems. During kharif, Ageratum sp. (28%) Cynodon dactylon (20%) and Commelina benghalensis (19%) were the predominant weeds. In rabi, Phalaris minor(63%) was the most dominating weedfollowed by Coronopus didymus (10%), Spergulla arvensis (6%) and Ageratum sp. (4%). In kharif, Commelina benghalensis was most abundant weed irrespective of the cropping system and was most dense in rice-based cropping systems. Ageratum sp. was most dense in other systems. Monochoria vaginalis was only present in rice-based cropping systems. Cynodon dactylon had highest important value index (IVI) irrespective of the cropping system followed by Commelina benghalensis, while Ageratum sp. was important in other cropping systems having higher IVI. Weed flora during rabi was richer than that during kharif. In rabi, Phalaris minor had highest abundance, density and important value index (IVI) irrespective of the cropping system. Coronopus didymus and Spergulla arvensis were the other important weeds having higher value of these indices. In traditional „rice-wheat‟ system 14 species in rabi and 8 in kharif season were found associated and species richness varied with diversification of systems. In rabi, highest diversity of weed species was in rice-wheat system and in kharif weed flora was more diverse in C3, C4 and C8 i.e. okra, turmeric and colocasia based systems and was lower in rice-based systems. C8 had highest RGEY, profitability, productivity, gross returns, net returns and B: C among all the cropping systems. C3 had highest land use efficiency. C1 had highest carbohydrate, protein yield and highest energy output with lowest input. C4 had highest cost of cultivation and lowest B: C and energy output: input. N depletion by weeds ranged from 16.2 in C6 to 48.5 kg/ha/annum in C3, P from 3.1 in C5 to 8.1 kg/ha/annum in C3 and K from 4.8 in C6 to 13.2 kg/ha/annum in C3. Weeds inflicted huge yield losses ranging from 30.6 in C1 to 59.2 % in C6.ennullThesis