Modelling seedbank dynamics of volunteer oilseed rape (Brassica napus )

A simple mechanistic model is presented which describes population dynamics of volunteer oilseed rape within a field. The model calculates the number of volunteers appearing in each crop and the seedbank after each crop. The main input variables are harvesting losses when the crop is oilseed rape, crop rotation, soil cultivation, soil moisture content within the arable soil layer and the level of volunteer control in each crop in the rotation. Simulation studies suggest that there are a number of agronomic means of minimising volunteer oilseed rape populations effectively. The amount of harvesting losses, the time span between oilseed rape harvest and the first tillage operation post-harvest, the efficiency of controlling oilseed rape in other crops and rotation itself are key components of a programme for ensuring that volunteer oilseed rape populations are minimised.

Simulation runs showed that the proportion of volunteer plants within a crop of oilseed rape will be relatively high, even though the density of volunteers is low in other crops. This contamination of a rape crop could be a particular problem in the context of the cultivation of genetically modified rape.

The model would benefit from improved estimates of some parameters. More data are particularly necessary on the long-term development of a seedbank of oilseed rape and the relationship between the size of the seedbank and the number of volunteers in various crops.