Quantifying aerial dispersal of pollen in relation to outcrossing in maize

The extensive adoption of genetically modified crops has led to a need to better understand the dispersal of pollen in the atmosphere because of the potential for unwanted movement of genetic traits via pollen flow in the environment. The aerial dispersal of maize pollen above a corn crop was studied by comparing field measurements of pollen concentrations with results from a Lagrangian stochastic (LS) model of pollen movement in the corn canopy and adjacent atmospheric surface layer. In August 2003, maize pollen was sampled up to 60 m above ground level (AGL) over a 26-ha cornfield using radio-controlled remote-piloted vehicles (RPVs) outfitted with remotely operated pollen traps and at 9 m AGL near the center of the field using Rotorod samplers. Usually, two RPVs were flown simultaneously at heights of about 30 m and 60 m AGL, while a third RPV was flown upwind of the source to sample any in-coming pollen. During several periods of pollen release, measured maize pollen concentrations averaged about 3.3 and 1.8 grains/m3 at heights of 30 and 60 m above the crop. Overall, the LS model predicted well the observed concentrations (within the expected uncertainty). Most of the cases where the model over- or under-predicted concentrations aloft were associated with unstable atmospheric conditions, where the use of Monin-Obukhov similarity theory is questionable at heights of 60 m AGL. To account for this, we are developing a coupled canopy-surface-layer/convective-boundary-layer model. Plans for testing the model over a wider range of atmospheric conditions will be described.