Climatology of Kansas Atmospheric Inversions and Impacts to Agricultural Herbicide Spraying Times

Climatology of Kansas Atmospheric Inversions and Impacts to Agricultural Herbicide Spraying Times

Jared Sinowitz^1,2

Christopher Redmond²

1. University of Kansas
2. Kansas Mesonet, Department of Agronomy, Kansas State University, Manhattan, KS

Abstract

In the agricultural heartland of Kansas, atmospheric inversions play a pivotal role in determining the effectiveness and safety of herbicide applications, especially in terms of their dispersion patterns and potential for off-target drift. This phenomenon is critical for ensuring the health of crops, the environment, and nearby communities. The nuances of this phenomenon, particularly how regional and local variations across the state interplay with the temporal windows allowable for herbicide application have not been evaluated in Kansas. Such research blind spots can result in inefficiencies in agricultural practices.

To bridge this gap, our study scrutinized short climatology patterns and their implications for the permissible duration for herbicide application. Using labeling requirements of common herbicides, optimal application parameters of wind speeds between 1.30 to 4.50 m/s, in conjunction with the presence of an inversion, or stable low levels of the atmosphere were considered. By analyzing the times that these conditions overlapped, we can see the differences in sprayable windows by area.

The Kansas Mesonet, a network of 80+ weather stations spread across the state, that provides data in five minute intervals, was utilized in this study. Analysis showed that regions situated in the western areas of the state consistently benefit from longer, extended windows for herbicide application when compared to the eastern regions of Kansas. This is the result of the local geography changing with increasing westward extent. We theorize that such variations can be linked to shifts in diurnal temperature cycles, vegetation types, prevailing wind patterns, and the unique topographical gradient that the state exhibits as one travels westward. It's essential to emphasize that even minor topographical or climatic shifts can result in significant changes in spraying conditions.

Diving deeper, we noted that the difference in air temperature from Mesonet stations in Northwest Kansas was significantly warmer (2.8 to 5.6 degrees Celsius) compared to those in Eastern and Southeastern Kansas. Western Kansas, characterized by its relatively flat terrain (with an average elevation of 900-1100 meters above sea level), offers a more conducive environment for efficient nighttime cold air drainage. This stands in contrast to the rolling hills of Eastern Kansas (averaging between 400 meters above sea level) where cold air drainage is limited to narrow valleys and not spread across a larger, flatter region like that of Western Kansas.. This topographical distinction means inversions, stable layers of the atmosphere where temperature increases with height, tend to be weaker and more localized than in the west. Topography allows for more effective solar heating earlier in the day and remaining effective later into the evening. This results in longer windows of spraying and earlier dispersion, along with later development of inversions during the evening. Such observations underscore the need to customize farming approaches based on specific regional characteristics. As a direct consequence, farmers in Western Kansas are provided with longer, more flexible periods suitable for spraying herbicides.

These variances in spray windows are particularly pronounced during the Spring months. This season is characterized by amplified temperature and moisture gradients stretching from the Western to Eastern parts of the state. Western KS is a more arid climate with less annual precipitation, contributing to higher temperatures compared to the East that has more moisture and slightly lower temperatures. The Spring period, therefore, serves as a prime indicator of the state-wide variations in spray conditions. Summer, with its higher temperatures across the entirety of Kansas and prolonged periods of an unstable atmosphere with light winds, further shows these regional differences. During these two seasons, Mesonet stations in the western sector of Kansas recorded an additional 45 to 90 minutes of permissible spraying time daily, a finding of significant value to the agricultural community.

An example of this difference can be characterized from data spanning March to May. Drawing from real-world data assists in illustrating the minute differences in sprayable times across Kansas. In Eastern Kansas in the Spring, nighttime inversions typically dissipated by 07:50, whereas in the West, this occurred earlier at 07:30. Often, the afternoon time period for safe spraying ended by 17:00 in the eastern regions and 18:00 in the west. This trend, while slightly muted due to higher temperatures state-wide and less nighttime cold air drainage, persisted into the summer months as well. Sprayable times initiated at 07:20 in the East and 07:10 in the West, concluding at 18:00 and 18:30 respectively in the Summer. All times mentioned are in Central Standard Time. In Summer, that time decreased to an extra 40 minutes. While not statistically significant at first glance, 40 minutes can be incredibly important for farmers looking to maximize their farm’s efficiency and/or avoiding off-target herbicide drift issues.

For farmers, understanding and adapting to these local and seasonal variations is crucial for improved farming efficiency, economic sustainability, and reduced environmental impacts. By better understanding the time that farmers can utilize to safely spray, we can better ensure that practices are environmentally friendly and economically viable. Lastly, this could also reduce the liability for potential off-target drift complaints or impacts.