Wheat and Grain Sorghum in Four-Year Rotations.

Research on 4-year crop rotations with wheat and grain sorghum was initiated in 1996 at the Kansas State University (KSU) Southwest Research-Extension Center (SWREC) near Tribune, KS. Rotations were wheat-wheat-sorghum-fallow (WWSF) and wheat-sorghum-sorghum-fallow (WSSF) along with continuous wheat (WW). Soil water at wheat planting averaged about 230 mm following sorghum, which was about 90 mm more than the second wheat crop in a WWSF rotation. Soil water at sorghum planting was approximately 30 mm less for the second sorghum crop compared with sorghum following wheat. Grain yield of recrop wheat averaged about 80% of wheat following sorghum; while grain yield of continuous wheat averaged about 60% of the yield of wheat following sorghum.  Wheat yields were similar following one or two sorghum crops. Similarly, average sorghum yields were the same following one or two wheat crops. Yield of the second sorghum crop in a WSSF rotation averaged about 65% of the yield of the first sorghum crop.