Dryland Winter Wheat as Affected by Previous Crops

The dryland winter wheat ( Triticum aestivum L.)–grain sorghum [ Sorghum bicolor (L.) Monech]–fallow (WSF) rotation is suitable for large areas of the U.S. Great Plains. Other crops such as corn ( Zea mays L.), sunflower ( Helianthus annus L.), and soybean [ Glycine max (L.) Merr.] can be substituted for grain sorghum, but the effects of these crops on the subsequent wheat crop have not been extensively documented. A study was conducted near Garden City, KS from 1992 through 1998 to determine the effect of these four crops on soil water at planting (SWP), yield, and yield components of the subsequent wheat crops. Wheat was grown following conventional tillage (CT), reduced tillage (RT), and no tillage (NT). On average, amounts of SWP following sunflower and soybean were 19.9% and 9.3% lower, respectively, than those following corn and sorghum. Grain yields following sunflower averaged 0.85 Mg ha −1 less than those following corn and sorghum in two of six years at all tillage levels, 0.72 Mg ha −1 less in one year with CT and NT, and 0.60 Mg ha −1 less than those following corn in one year with CT and RT. Yields following soybean were 0.61 Mg ha −1 less than those following RT corn in one year and 0.61 Mg ha −1 less than CT corn and CT sorghum in one year. Most of these yield reductions were caused by fewer heads m −2 , but fewer kernels head −1 and lower kernel weight occasionally contributed. Sunflower and soybean may cause reductions in subsequent wheat yields, but they provide diversification and may prove beneficial when the whole cropping system is considered.