Asymmetric competition between wheat and weeds - a step to improve crop-weed interaction models

Asymmetric competition is a form of interactions among plants, in which lar ger plants obtain disproportionate share of the contested resources (light, water, nutrients) and suppress the growth of their smaller neighbours. Thi s way, in which plants are competing, is more pronounced in interspecific c ompetition because of species-specific differences in growth dynamics at th e onset of competition. In the model experiments competition between wheat and Galium aparine and e ffect of initial seedling size on growth dynamics were studied. The higher the initial advantage of one species, the stronger effect on the growth rat e by competition. This initial size-differences between competing species h ad greater influence on their growth than plant density. The fast growth of wheat plants at the onset of competition is a reason for higher competitiv e effects towards Galium aparine plants than the other way round. Using sim ulated data from this relationships, we prove size asymmetry in competition between wheat and Galium aparine. The use of asymmetric competition model in economic threshold concepts or to determine critical period thresholds a re discussed.