Effects of Solanum nigrum L. Density On Agronomic and Yield Traits, Physiological Indexes, and the Economic Threshold of Mechanically-harvested Cotton

Solanum nigrum L. is a malignant weed in cotton fields and an important factor affecting cotton yield. However, the relationship between S. nigrum density and cotton yield losses remains unclear. This study examined the effects of different S. nigrum densities (0 (control group), 1, 4, 7, 10, and 15 plants/m²) on the agronomic traits, physiological indexes and yield traits of cotton. The results were then used to establish a mathematical model of the relationship between S. nigrum density and the rate of cotton yield loss. Density significantly affected plant height, stem diameter, the number of main stem nodes, and contents of nitrogen, phosphorus, potassium, and soluble sugar in the cotton leaves at seedling, budding, and flowering and boll stages. A significant effect on the soluble protein content was also observed at the seedling stage. Moreover, S. nigrum significantly reduced the boll number and subsequent yield, with losses of 100% at a density of 15 plants/m². In contrast, no significant effects on the single boll weight or fiber length and fiber uniformity were observed. The resulting mathematical model of S. nigrum density (x) and the rate of cotton yield loss (y) conformed to the logarithmic function y = 12.594lnx + 58.025. Meanwhile, the economic threshold of manual weeding and application of 96% S‑metolachlor EC were then calculated as 160 and 170 plants/hm², respectively. These findings suggest that density is the key factor affecting S. nigrum damage in cotton fields, highlighting the importance of early management and control.