<p>This study aimed to determine whether the application of winter fallow weeds can improve grain yield in rice (<i>Oryza sativa</i>) and, if so, to identify the key yield attributes and plant traits contributing to the yield improvement. The findings are expected to offer valuable insights into the potential of winter fallow weeds as an organic fertilizer source for rice production. A fixed-field experiment was conducted over four years (2020 − 2023) to investigate the impacts of applying winter fallow weeds (500 g m⁻², dry basis) on grain yield, yield attributes, and related plant traits under three nitrogen (N) rates (0, 150, and 225 kg ha⁻¹) in rice. Applying winter fallow weeds increased rice grain yield by 6% across three N rates and four years. The application of fallow weeds led to increases of 6% in panicles per m², 2% in grain weight, and 9% in total biomass production across various N rates and years. The increase in panicles per m² was due to a higher number of maximum tillers per m². The increase in grain weight was linked to a rise in photosynthetic capacity during the grain-filling stage. The increase in total biomass production was attributed to greater intercepted radiation and improved total N uptake. The application of winter fallow weeds has significant yield-increasing effects by improving growth and physiological processes in rice. This study underscores the potential of winter fallow weeds as an organic fertilizer source for improving grain yield in rice.</p>