Frequency of Spring versus Autumn Precipitation in the Northern Corn Belt

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, however, 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.