Seeding and Nitrogen Rates Required to Optimize Winter Wheat Yields following Grain Sorghum and Soybean

No-till planting winter wheat (Triticum aestivum L.) following summer crops requires different crop management than continuous wheat. A 3-yr study was conducted to determine if increased seeding rates and N fertilizer rates were required to maximize wheat grain yields following grain sorghum [Sorghum bicolor (L.) Moench] and soybean [Glycine max (L.) Merr.]. Wheat seeding rates of 67, 101, 134, and 168 kg ha−1 and N treatments of 0, 45, 90, and 134 kg N ha−1 were applied to areas previously planted to grain sorghum and soybean. Grain yield increased as seeding rate increased in all 3 yr, with yield optimized at seeding rates of ≥134 kg ha−1 regardless of the previous crop. Wheat response to N varied with previous crop, with wheat following grain sorghum requiring 21 kg ha−1 more N to maximize grain yields compared with wheat planted after soybean. These previous-crop effects were attributed to grain sorghum producing higher levels of residue and this residue immobilizing a greater amount of available N than soybean residue. Leaf N content decreased as seeding rates increased and increased as N rates increased. Leaf N content had a similar response to N rates and previous crops as grain yields. Grain N content increased as applied N increased. Results of this study indicate that different seeding and N rates are required to optimize wheat yields when no-till planted after grain sorghum and soybean.