Mining the record: historical evidence for climatic influences on maize –Abutilon theophrasti competition

Variations in climate are widely recognized as central factors governing the competitive balance in mixedspecies plant communities. In agricultural systems, highly variable patterns of crop yield reduction as a function of weed density have been documented across sites and among years at the same site for several crop–weed combinations. This variation is typically attributed to contrasting environmental conditions. Despite broad acknowledgement of their importance, experimental and temporal limitations have constrained the investigation and systematic understanding of environmental controls on the dynamics of competition. For several well-studied crop–weed associations, aggregating historical data from similar competition experiments provides an opportunity to explore interference relationships over an array of conditions. In this study, 19 site-years of maize – Abutilon theophrasti (velvetleaf) data were compiled and the weather characterized (i.e. average ambient temperature and moisture regime) for discrete portions of each growing season. These features were then related to patterns of maize yield loss from A. theophrasti interference at highweed densities. Results of this analysis suggest that temperatures following establishment, together with the presence or absence of water stress during the maize crop’s exponential growth phase, account for over 60%of the observed variation in relative yield loss.