Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 10, 2000
Publication Date: N/A
Interpretive Summary: Agricultural chemical companies have licensed various herbicides for autumn application in the northern Corn Belt. Herbicides that are applied in the autumn, however, may be more susceptible to loss by runoff or leaching than those applied in the spring. Autumn applications therefore could threaten the quality of our surface and groundwater systems. In an attempt to determine the potential fate of herbicides applied during different seasons, I examined the frequency of daily rainfall events in the autumn and spring for 15 climate stations across the northern Corn Belt. This examination found that precipitation occurs with greater frequency in the spring than autumn. Therefore, autumn-applied herbicides may be less susceptible to leaching and runoff as compared to spring-applied herbicides. Farmers may use this information to plan their spring and autumn planting seasons.
Technical Abstract: Agricultural fertilizers and pesticides are applied in both the spring and autumn in the northern US Corn Belt. Loss of chemicals through leaching or runoff is in part dependent on the frequency of precipitation after application. Little is known, however, concerning the seasonal variability in frequency of daily precipitation events in the northern Corn Belt. The frequency distribution in spring and autumn precipitation events were examined at 15 climate stations in Iowa, Minnesota, South Dakota and Wisconsin. The frequency of daily precipitation in the spring increased from NW to SE whereas in the autumn the frequency increased from W to E across the Corn Belt. The frequency of spring events was 200% greater at westerly stations and 30% greater at easterly stations compared with autumn events. This study suggests that agricultural chemicals applied in the autumn may be less susceptible to leaching and runoff due to less frequent rains in the autumn than in the spring in the northern Corn Belt.