Field measurements of airborne concentration and deposition rate of maize pollen

In recent years there has been interest in the dispersal of maize (Zea mays) pollen from crops, particularly in relation to gene flow and seed quality. We report the results of experiments that measured maize pollen dispersal from a 20 m x 20 m experimental crop. The experiments were done in a commercial farm in France during the summer of 2000. Pollen production was estimated to range from 10(4) to 2 x 10(6) grains per day per plant. Pollen concentrations and deposition rates decreased rapidly with distance from the crop: concentrations decreased by about a factor of 3 between 3 and 10 m downwind of the source deposition rates at 30 m were < 10% of those at 1 m. Horizontal flux of pollen were estimated from pollen concentration and wind speed profiles using a mass balance approach, and ranged from 15 to 560 grains m-1 s-1 at 3 m from the source. Comparison of deposition rates estimated with the mass balance and direct measurement suggests that only a small proportion of the pollen released from the crop would have been still airborne at distances greater than 30 m downwind. Deposition velocity determined as the ratio of the deposition rate to the airborne concentration at 3 m from the source averaged 0.6 m s-1, which is twice as large as the settling velocity for maize pollen.