Can weeds enhance profitability? Integrating ecological concepts to address crop-weed competition and yield quality

1. Sustainable cropping systems are needed for future food security. One aspect of sustainable cropping is to manage for desirable grain quality of crops including seed size, protein, oil and metabolite composition. 2. Plant ecology theory on niche relationships and interspecific competition predicts that subordinate species mixtures (i.e. weed species) will affect dominant (i.e. crop) species offspring quality. Beyond individual weed species effects on crop quality, we hypothesise that the integrated effect of weed mixtures will be influenced by taxonomic, functional trait and phylogenetic diversity. 3. Reviewing Glycine max (soybean)-weed systems, we show a complex relationship between the weed community and G. max seed protein, oil, mean seed mass and physiological markers (relative water content, trigonelline leaf content, fluorescence, foliar Cu, Fe and Zn). Increased levels of weed competition led to increased seed protein, at the expense of seed oil. 4. Synthesis. We propose that research on interspecific relationships between crops and weeds consider weed species diversity, weed functional traits associated with the Leaf-Height-Seed strategy and phylogenetic relationships to identify weed mixtures (either sown or manipulated through herbicide control) best suited to minimise their detrimental effects on yield while maximising crop quality as part of sustainable cropping systems.