Wind Increases Stress
- Wind can exacerbate heat stress by increasing the VPD between the leaves and the air immediately surrounding them.
- When water is evaporated from plant leaves, the air above the surface gradually becomes more saturated with water vapor.
- If winds are low, this layer of saturated air stays in place around the crop canopy, causing the evapotranspiration rate to decrease (Figure 3).
- When winds are high, this layer of saturated air is constantly being removed and replaced with drier air (Allen et al., 1998).
- At high relative humidity, wind speed will matter less, as the wind will only be able to replace the saturated air with slightly less saturated air.
- Under arid conditions though, small variations in wind speed may result in larger variations in VPD and evapotranspiration.
Figure 3. Illustration of the effect of arid wind on the microclimate of the crop canopy.
- The more severe stress along the field edge is likely due to the fact that the air is driest when it encounters the leading edge of field and picks up moisture as it moves across the crop canopy (White and Licht, 2020; Westgate and Vittetoe, 2017).
- Consequently, the effect of wind on VPD is greatest for plants near the field edge and lower for plants in the rest of the field (Figure 3).
Figure 4. Corn field showing stress symptoms along the edge of the field where it is bordered by soybeans and CRP, but no symptoms where it is bordered by corn (September 2021).