The effects of water stress and planting density on the competitive relationships, yield performance, and
dynamics in canopy dominance of cowpea [Vigna sinensis (L.) Savi ex Hassk] and redroot pigweed (Amaranthus
retroflexus L.) grown in pure and mixed stands were investigated under glasshouse and field conditions. Results showed
that water stress at early growth stages reduced plant height, shoot dry weight, leaf area, leaf dry weight and lowered pod
dry weight of cowpea, and inflorescence dry weight of A. retroflexus. The effect on both species was more pronounced at
high planting densities as a result of severe intraspecific competition. In pure stands, cowpea was affected more than A.
retroflexus and the effect was more pronounced on reproductive organs development. Growth analysis of both species
grown in pure stands for different periods indicated that leaf area was the most descriptive variable in shoot dry weight
and total dry weight of both species at early growth stage. A. retroflexus grew at a faster rate with higher net assimilation
rate per unit leaf area and allocated more resources to leaves and roots than did cowpea. Results showed that A. retroflexus
was stronger competitor than cowpea. Competition reduced growth and competitive abilities of both species mainly by
reducing leaf area early in growth but the effect was more pronounced on cowpea.