Weed community composition and diversity in long-term conservation agriculture-based maize-wheat-green gram rotation: Impacts of tillage, residue, and nitrogen

Weed interference remains a major challenge to the widespread adoption of conservation agriculture in the Indo-Gangetic Plains. This study was designed to assess the long-term effects (>12 years) of integrated tillage (conventional and zero tillage), residue, and nitrogen (applied at 50%, 75% and 100% of the recommended dose) management on weed abundance, diversity, and community structure in a maize-wheat-green gram rotation. Long-term adoption of conservation agriculture promoted the dominance of a few broad-leaved weed species (relative abundance: 74.2–77.4% in maize, 96.8–98.2% in wheat, and 74.1–74.9% in green gram), resulting in a more homogeneous weed community, whereas conventional tillage supported a more diverse and evenly distributed weed flora with a higher prevalence of grassy species. Zero tillage combined with residue retention and higher nitrogen rates (75% and 100%) significantly reduced weed density by 58.8% in maize, 55.4% in wheat and 59.7% in green gram compared with conventional tillage, highlighting the greater weed-suppressive effect of conservation agriculture practices. These treatments accounted for 20–56% of the variation in weed community composition, with distinct indicator species associated with the tillage-residue-nitrogen treatments, indicating that weed community structure was shaped primarily by the combined implementation of conservation agriculture practices and higher nitrogen fertilization. The findings support a shift towards preventive and integrated weed management in conservation agriculture, in which tillage, residue, and nitrogen are strategically combined to manipulate weed community structure and target weed-specific management, rather than relying solely on generalized control measures.