Weed Biomass Predicts Yield Loss in Cotton and Wheat Under Contrasting Tillage and Weed-Management Practices

Weed infestation remains a major constraint to cotton and wheat productivity in South Asian cropping systems, and the tillage system adopted further modulates weed pressure and control efficacy. The present two-year field study evaluated the interactive effects of tillage (conventional and zero tillage) and weed-management strategies, herbicide, mechanical weeding, crop residue mulch, plastic mulch, and living mulch, on weed dynamics and yield in a cotton–wheat system over two seasons (2024–25 and 2025–26). Weed management, tillage, and their interaction significantly affected density and dry biomass of grassy, broadleaf, and sedge weeds in both crops (p < 0.05). Herbicide and plastic mulch resulted in higher weed suppression, lowering total weed density by 82–92% in cotton and over 89–92% in wheat, with weed control efficiency of 75–93%. Plots under conventional tillage, which also differed in row spacing, recorded up to 18% less weed pressure than zero tillage plots, as this difference may reflect both soil disturbance and planting geometry. Cotton lint yield increased by up to 184–191% over the weedy check under herbicide with conventional tillage, and wheat grain yield showed a comparable response. Yield declined linearly with early-season weed dry biomass in both crops. Cotton was more sensitive per unit weed biomass than wheat, though the slope was unaffected by tillage. These results show that plastic mulch and herbicide, paired with suitable tillage choice, are the most reliable options for limiting weed-related yield loss and offer a basis for herbicide-efficient weed management in cotton–wheat systems.