In the first place, faster speeds require higher flow rate nozzles, which produce a coarser spray. This should favour the penetration of stubble. On the other hand, faster speeds cause the spray's movement to become more horizontally oriented, even if the nozzles point straight down. Canopy Microclimate Wind velocities near the ground are significantly lower in a stubble canopy than on bare soil. Velocity reductions were most dramatic at low wind speeds and closer to ground level.
Wind velocity can have major effects on early plant growth and development.
Stubble 14.8 1.1 Bare 7.8 0.4 As a result of the differing environments, plants grown in the stubble proved to be more susceptible spray targets. This effect could be due to greater spray capture by the larger projected leaf area, increased presence of soil pathogens, or more permeable cuticles of the plants grown in a stubble environment. The reduction of spray drift will always be an important goal for applicators. There are relatively few days available for spraying, and applicators must make the most of the time they have available. But for those practicing conservation tillage, a stubble canopy provides a unique beneficial factor that is not mentioned in traditional publications on spray drift.