Soybean Variety Selection for Early Planting Dates.
Jason L. De Bruin and Palle Pedersen. Iowa State University, 2104 Agronomy Hall, Ames, IA 50011-1010
Planting date and variety selection are important management decisions for maximizing soybean yield. In Iowa the recommendation is to begin planting soybean by the end of April, earlier than previous recommendations. Soilborne pathogens modify the yield potential of an environment potentially reducing the benefit of early planting and increasing the importance of variety selection. Experiments were established at three locations for three years to evaluate the interaction between soil fumigation, used to modify soil pathogen populations, and the agronomic choices of planting date and variety selection. The experimental design was a randomized complete block design in a split-split plot arrangement with four replications. Soil fumigation was the main plot and four planting dates and six soybean varieties were the split and split-split plot, respectively. No main effect occurred due to soil fumigation. However, a soil fumigation by variety interaction was found in 2005, specifically for varieties NK-S32-G5 and P91M90. Early planting resulted in a yield advantage of 670 kg ha-1 compared to planting the first week of June across all environments with a benefit of 888 to 1800 kg ha-1 in high yield environments and 0 to 670 kg ha-1 in low yield environments. A planting date by variety interaction was detected in 2004 at two of the three locations as the two highest yielding varieties were more affected by delayed planting. Yields were similar for all varieties at late planting. It was concluded that early planting is necessary for a variety to reach its full yield potential. Early planting should be an objective for growers and the current method of selecting high yielding adapted varieties should remain a priority regardless of planting date.