Dynamics of competition between wheat and oat: I. Effects of changing the timing of phenological events

dSupply and demand for resources change dynamically throughout the growing season. If we are to understand the differences in competitiveness among crop cultivars, we need to study the dynamics of species interactions, not just their outcomes. We examined the temporal patterns in competition between wheat (Triticum aestivum L.) and oat (Avena sativa L.) in a series of field experiments. The combined effects of shifts in height growth and phenological development were described for monocultures and mixtures by varying the sowing dates of the species. Similar observations were made for oat competing with wheat lines differing in flowering time and for wheat competing with a range of Avena taxa. In contrast to earlier work, no reversals of competitive hierarchy were seen during the season. The species that achieved the greater biomass early on remained the better competitor throughout growth. The hypothesis that a delay in emergence will move the timing of such reversals was thus not supported. There were few differences in patterns of the dynamics of competition among Avena taxa and no observable differences in competitiveness among wheat lines differing by up to 6 d in flowering date. Overall, the results support the idea that reversals in competitive hierarchy during the season are caused by relative patterns in plant height growth of competitors and may occur only in systems in which competition for light is dominant. Otherwise, an early competitive hierarchy will be maintained throughout the growing season.