Competitive Effects and Economic Threshold of Silybum marianum in Winter Wheat Under Different Nitrogen Fertilization Levels

Abstract

Winter wheat is one of the most important cereal crops cultivated worldwide; however, its productivity is significantly affected by weed competition and improper nutrient management. Silybum marianum (milk thistle), a highly competitive broadleaf weed, has emerged as a serious threat in wheat-growing regions due to its rapid growth, high nutrient uptake capacity, and interference with crop development. The present study was conducted to evaluate the competitive effects and economic threshold of Silybum marianum in winter wheat under different nitrogen fertilization levels. Field experiments were carried out using varying weed densities and nitrogen application rates to assess their influence on wheat growth, yield components, and grain yield. Data on plant height, tiller production, biomass accumulation, and yield reduction were recorded and analyzed to determine the extent of crop–weed competition. Economic threshold levels were estimated by integrating yield loss data with weed management costs and market value of wheat grain. The results demonstrated that increasing densities of Silybum marianum significantly reduced wheat growth and yield, while higher nitrogen fertilization levels enhanced both crop and weed growth. The competitive ability of the weed was found to increase under elevated nitrogen availability, leading to greater yield losses in untreated plots. Economic threshold analysis revealed that timely weed management at lower weed densities was economically beneficial, particularly under moderate and high nitrogen conditions. The study highlights the strong interaction between nitrogen fertilization and weed competition in winter wheat ecosystems. These findings emphasize the importance of integrated nutrient and weed management strategies for minimizing yield losses and improving the economic sustainability of wheat production systems. Effective early-season control of Silybum marianum is therefore essential to maintain optimum crop productivity and profitability.