Early growth and development of wild radish (Raphanus raphanistrum L.) in relation to wheat

Raphanus raphanistrum was grown in monoculture and as a range of cohorts of emergence in mixture with wheat. Growth and development were recorded at f requent intervals up to anthesis of the wheat. R. raphanistrum remained sho rter than wheat, only over-topping the crop prior to anthesis for 2 of 7 so wing dates. When expressed in terms of photothermal time, growth in monocul tures was similar for all sowing dates except those for wheat in mid-summer . Even a short delay in R. raphanistrum emergence in mixture decreased its growth considerably; R. raphanistrum emerging more than 4 weeks after the c rop had no detectable effect on the wheat. However, even R. raphanistrum pl ants emerging 10 weeks after the crop produced some seeds. In mixture, R. r aphanistrum had a higher specific leaf area (SLA), reduced leaf partitionin g, and taller stems than in monoculture. A physiological growth model based on parameters from monocultures was unable to predict growth in mixtures; inclusion of changes in SLA and height in mixture improved predictions in s ome cases. It is concluded that competition models based on monoculture par ameters, although previously successful for species with similar height and phasic development, are unlikely to work for species that differ in these attributes. Further work is required on the physiology of plants within mix tures.