Simulation and field experiments of designs for pollen confinement

We have examined the usefulness of biological windbreaks for reducing the transport of fugitive pollen (such as that from genetically modified crops). First, we evaluated various confinement strategies using a coupled modeling approach that combines a model of wind and turbulence around porous obstacles with a Lagrangian-stochastic model for particle motion and deposition. Then, we tested a confinement strategy during field projects in the 2005 and 2006 growing seasons. Here we examined the usefulness of a tall annual grass (sorghum sudangrass) as a border; such a border is much less costly and labor-intensive than erecting a structure, and the border grows more quickly than trees. Field measurements for both 2005 and 2006 showed that a sorghum sudangrass border around a small maize plot reduced the wind speed over the maize canopy by about 1 m/s on average. There was an even larger effect on gusty winds, with the maximum wind gust recorded in the open plot being 8.1 m/s while the maximum gust in the bordered plot was only 5.5 m/s. The field results also showed that the vegetative border reduced pollen transport downwind from the source plot. The windbreak reduced the maximum distance of pollen dispersal from 300 m to 160 m. These results show that the tested design provides a simple and economical means to reduce the escape of transgenes from a source.

Field studies are expensive and time-consuming to perform, so that the number of configurations that can be tested in the field is severely limited. We propose that the combined models used here are advantageous as a screening tool to test the effect of border design, field geometry, wind climatology, and other factors on pollen transport. This allows field studies to focus more efficiently on designs that are likely to be successful.