Reproductive development and then timing of seed dispersal in many weeds is positively correlated with intensity/availability of environmental resources. In this study, we investigated the effects of nitrogen availability and the type of the crop on timing of weed seed dispersal. Two agricultural weeds; wild barley (Hordeum spontaneum Koch.) and wild mustard (Brassica kaber (DC.)) were grown in wheat and oilseed rape crops under a range of nitrogen levels. H. spontaneum seeds that developed under no or low nitrogen levels (0 and 60 kg ha -1 ) reached their final maturation stage sooner than those that developed under high nitrogen levels (120 and 240 kg ha -1 ), resulting in an earlier seed dispersal (109 and 76 degree-days where grown in wheat and oilseed rape cropping systems, correspondingly). In all nitrogen levels, H. spontaneum seeds developed in wheat crop reached their maturation stage sooner, and were then dispersed sooner than those developed in oilseed rape cropping system. The results of this study could help growers to make the best decision on weed management through management of seed dispersal. High nitrogen application, for example, with an early harvest may mean that a significant proportion of seeds are taken up to the combine harvester traveling long distances as grain impurity. In contrast, low nitrogen application with a late harvest may result in the majority of seeds falling to the ground and increasing subsequent crop interference. Therefore, an infested crop should be harvested as early as possible to reduce the quantity of weed seeds entering the seed bank.