Weed flora of aerobic rice and their effect on growth, yield and nutrient uptake by rice Oryza sativa in the coastal region of Karaikal of Puducherry, India

A field experiment was conducted at farm lands of Pandit Jawaharlal Nehru College of Agriculture and Research Institute, Karaikal to know the weed floristic composition and their effect on growth, yield and nutrient uptake by aerobic rice (Oryza sativa). The results revealed that totally 29 species of weeds from 22 genera belonging to 17 families were noticed. Among them, four were grasses, six were sedges, and nineteen were broad leaved weeds. Of this 29 species, four were perennials, and the rest were annuals. During initial stages (30 DAS), sedges dominated (38.3%) whereas at later stages (60 DAS) broad leaved weeds dominated the aerobic rice fields (42.5%). Grasses were found to be comparatively less dominant at both the stages. Echinochloa colona Link. (28.1%) followed by E. cruss-galli (L.) Beauv. (6.1%) among the grasses; Cyperus difformis L. (19.8%) followed by C. iria L (9.9%) among the sedges and Ludwigia abyssinica (28.0%) among the broad leaved weeds, were the predominant weed species in aerobic rice cultivation. Weeds, when left unchecked, competed with rice for all resources like nutrients, space, light and soil moisture. The unweeded control recorded the maximum nutrient depletion by weeds (76.6, 6.4 and 106.8 Kg of N, P andK ha-1 ). Due to severe competition, weeds suppressed the growth of rice which resulted in lower growth and yield attributes leading to lower grain (333 kg ha-1 ) and straw yields (1903 kg ha-1 )