Growth Analysis and Responses of Cowpea [Vigna Sinensis (L.) Savi ExHassk.] and Redroot Pigweed (Amaranthus retroflexus L.), Grown in Pureand Mixed Stands, to Density and Water Stresses

摘要

The effects of water stress and planting density on the competitive relationships, yield performance, anddynamics in canopy dominance of cowpea [Vigna sinensis (L.) Savi ex Hassk] and redroot pigweed (Amaranthusretroflexus L.) grown in pure and mixed stands were investigated under glasshouse and field conditions. Results showedthat water stress at early growth stages reduced plant height, shoot dry weight, leaf area, leaf dry weight and lowered poddry weight of cowpea, and inflorescence dry weight of A. retroflexus. The effect on both species was more pronounced athigh 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 speciesgrown in pure stands for different periods indicated that leaf area was the most descriptive variable in shoot dry weightand total dry weight of both species at early growth stage. A. retroflexus grew at a faster rate with higher net assimilationrate per unit leaf area and allocated more resources to leaves and roots than did cowpea. Results showed that A. retroflexuswas stronger competitor than cowpea. Competition reduced growth and competitive abilities of both species mainly byreducing leaf area early in growth but the effect was more pronounced on cowpea.