Effect of Water Stress on the Growth and Fecundity of Common Waterhemp (Amaranthus rudis)

Common waterhemp is one of the most commonly encountered and troublesome weeds in the midwestern United States. It is well known that water stress adversely affects crop growth and yield; however, the effects of water stress on weed growth and seed production are poorly understood. The objective of this study was to determine the effects of degree and duration of water stress on growth, development, and fecundity of two common waterhemp biotypes in greenhouse experiments conducted at the University of Nebraska-Lincoln. No difference was observed in growth, development, and seed production between two biotypes in response to degree and duration of water stress; therefore, data were combined. The degree of water stress study included five treatments, where the amount of water applied to each pot at 2-d interval was equivalent to 100, 75, 50, 25, and 12.5% of pot (soil) water content. The highest plant height (163 cm), number of leaves (231 plant^-1), and growth index (4.4 × 10⁵ cm³) were recorded at 100% of pot water content (no water stress). Similarly, aboveground biomass, total leaf area, and seed production reached their maximum at 100% of pot water content treatment, whereas they were reduced as degree of water stress increased. The study of water stress duration included five treatments, where amount of water applied to each pot at 2-, 4-, 6-, 8-, and 10-d intervals was equivalent to 100% of pot water content. The highest plant height (150 cm), number of leaves (210 plant^-1), and growth index (3.8 × 10⁵ cm³) were observed at 2-d interval of water stress, whereas seed production was similar at 2-d (36,549 seeds plant^-1) and 4-d (34,176 seeds plant^-1) intervals. This study shows that common waterhemp has capacity to survive and reproduce even under a higher degree and duration of water stress. Nomenclature: Common waterhemp; Amaranthus rudis Sauer.