Physiological indices to yield variation under rice-weed competition in direct seeded lowland condition

The efficacy of the six were evaluated on yield of rice cultivar Govind in direct seeded lowland rice ecosystem. The study revealed that hand weeding was superior to the chemical weed control for all the growth and yield attributes, reflecting higher grain yield of 3245 kg ha-1 in clayey loam soil during rainy season because of frequent elimination of weeds that resulted in the reduced weed competition. In direct seeded lowland rice, herbicide oxyfluorfen @0.24 kg/ha can effectively control weeds of rice such as grasses, sedges and broadleaved weeds if applied as one pre emergence at 1 days after sowing (DAS) . Even though some phytotoxicity effect was noticed on rice seedlings pertaining to reduction in plant height and total number of tillers but the seedlings recovered and resulted in higher grain yield of 2987.5 kg ha-1 and total dry matter of 227.9 g m-2 but lower than hand weeding practice. The lower yield of 7.9%ha-1 by oxyfluorfen application might be due to weed competition and might have resulted from the phytotoxicity and resultant shock experienced by the crop due to phytotoxicity during the seedling stage. On the other hand, application of herbicide significantly increased the leaf area index (LAI), relative growth rate (RGR), net assimilation rate (NAR) and crop growth rate (CGR) as well as increased carbohydrate and starch content over unweeded check.