MIDWESTERN CORN YIELD AND WEATHER IN RELATION TO EXTREMES OF THE SOUTHERN OSCILLATION

Weather and crop yields in the Midwest have exhibited wide fluctuation s during the past 10 yr. Sea surface temperatures (SST, El Nino and it s counterpart, La Nina) have been related to or blamed for these weath er abnormalities via teleconnections. Yield, weather, and El Nino rela ted (southern oscillation index - SO) data beginning in 1900 were asse mbled to determine if significant relationships could be ascertained. Midwestern weather and corn (Zea mays L.) yield data were coded relati ve to the SO. The SO groupings were <-8.0 (El Nino like, low phase), > 0.8 (La Nina like, high phase), and in between. Yields were grouped >1 0% or <10% relative to expected, or in between. Corn yields exhibited wide variation when the SO was in between, indicating that weather fac tors other than SO influenced corn yield during those oceanic conditio ns. However, when summer SO was in the high phase (low phase), there w as a statistical tendency for corn yields to be lower (higher) than ex pected, respectively for all Corn Belt states studied, except Missouri . The low (high) phase of the SO is generally related to El Nino (La N ina). During the low (high) phase of the SO, much of the Corn Belt rec eived more (less) rainfall in July, August, and September. At the same time, high temperatures-or heat stress-were generally lower (higher) during the low (high) phase of the SO. Both high (but not excessive) p recipitation and lower temperatures are associated with good corn yiel d. If El Nino forecasts improve as is expected, Midwestern corn yield forecasts should similarly improve.