Temporal dynamics of seed predation upon shed seeds of oilseed rape (Brassica napus L.)

Control of oilseed rape (Brassica napus L.) volunteers represents a big challenge to farmers since they compete with subsequent crops. During the harvest, large quantities of seeds are shed on the soil surface, where they either germinate or enter soil seed bank. Seed predation may represent a natural means of mortality of these seeds. in this study the temporal dynamics of predation upon rape seeds on the soil surface and the nature of the seed predators were studied in two localities (Praha-Uhrineves and Praha-Ruzyne) and two seasons (2006 and 2007). Temporal dynamic was studied using seed cards, presented in 3-4 sampling dates inside the plots with organic winter rape. The exposure continued for 7 days, during which invertebrates were collected using pitfall traps. The cards were put either in a cage which prevented vertebrate predators from predation on seeds, or freely so all surface active predators could eat the seeds, in order to reveal the nature of the predators. Seed predation varied with time and between sites in both years. No effect of caging was found in 2006 but appeared in spring 2007 in Praha-Uhrineves. No correlation between seed predation in cages and activity density of carabid beetles was found in any of the sites and years, suggesting that other underlying processes affecting the dynamics of seed predation are involved.