Competitiveness of erect, semi-erect, and prostrate cowpea (Vigna unguiculata) genotypes with sunflower (Helianthus annuus) and purslane (Portulaca oleracea): Experiments and simulations

Competition of erect, semi-erect, and prostrate cowpea [ Vigna unguiculata (L.) Walp.] cover crop and sunflower ( Helianthus annuus L.) or purslane (Portulaca oleracea L.) was studied by glasshouse replacement series, field experiments, and simulation modeling. Three cowpea genotypes differed in their ability to compete with sunflower and purslane, with the erect genotype IC as the most competitive genotype. Replacement series with six cowpea genotypes confirmed the finding. Correlation and regression between aggressivity indices of cowpea genotypes and growth parameters showed that faster plant growth, more dry matter partitioning into stem, and faster height growth were important determinants of competition with sunflower. Larger plant size and more dry matter partitioning into leaves were more important to the competitive outcomes when cowpea genotypes were grown with purslane. The ecophysiological simulation model INTERCOM was used to simulate competition of cowpea genotypes and sunflower or purslane. The model accurately simulated field competition of cowpea genotypes with sunflower, but not with purslane. The simulation model of cowpea and sunflower was used to study the effect of management practices and cowpea growth traits on cowpea and sunflower biomass. The model suggested that cowpea density and sunflower emergence date had significant effects on both cowpea and sunflower biomass, and that faster leaf area growth rate early in the growing season had the greatest effect on competitive outcomes among the studied growth variables. All of the above effects became less important as sunflower density increased. The simulation model, combined with field experiments, provides a new approach to studying the mechanisms of plant competition.