Effect of Tillage and Cultivar on Plant Population, Sudden Death Syndrome, and Yield of Soybean in Iowa

Conservation tillage has become a common practice of soybean farming in the Midwestern United States owing to the benefits of soil and moisture conservation. Field trials were established in a field with a history of sudden death syndrome (SDS; caused by Fusarium virguliforme) in Iowa in 2011 and evaluated for five consecutive years to determine the impact of tillage on SDS and yield. The experiment was laid out in a split-split-plot design with four replicates. The main plot factor was tillage (no-till both crops, no-till corn and chisel plow soybean, and disc corn and chisel plow soybean), and each main plot was divided into subplots of corn or soybeans (in a 2-year rotation). Each subplot was again divided into two subsubplots, in which two soybean cultivars, moderately susceptible (MS) and moderately resistant (MR) to SDS, were planted each year. Root rot and SDS disease index (FDX) differed among years, because some years were more favorable for the disease than the others. However, tillage did not affect any parameters, including yield, in any year (P > 0.05). Cultivar effect was significant for each parameter occasionally. When significant, the MR cultivar had lower root rot and FDX and greater yield than the MS cultivar. These data suggest planting resistant cultivars can be an effective management tactic, but tillage does not help for SDS management.