Soybean [Glycine max (L.) Merr.] rotation has been shown to enhance grain sorghum [Sorghum bicolor (L.) Moench] growth and yield due in part to N contribution. Grain yield, yield components, quality parameters, and water and NO3-N were measured on a long-term rotation study in 2003 and 2004 on a Sharpsburg silty clay loam (fine, montmorillonite, mesic Typic Arguidoll). The cropping treatments were: continuous soybean, continuous grain sorghum, grain sorghum-soybean, and soybean-grain sorghum rotation. Soil amendment treatments consisted of control, manure (17 to 26 Mg dry matter ha-1), and N (84 kg ha-1 for sorghum). The objectives were to: (i) separate biologically fixed N from other rotation effects on sorghum grain and stover yields; and (ii) determine the effect of cropping sequence and soil amendment on grain quality as measured by grain protein concentration, bulk density, and hardness. In 2003 and 2004, cropping sequence x fertilizer effects were present for most parameters measured. Irregardless of cropping sequence, manured plots had the highest grain and stover yields, grain N concentration, and kernel hardness measured by Tangential Abrasive Dehulling Device (TADD). Without soil amendment application, sorghum following non-nodulating soybeans had the lowest grain and stover yields. Kernel weight, test weight (bulk density) and true density were influenced to a small degree by treatments. Sorghum yield results suggested that biologically fixed N effects of soybean rotation accounted for approximately 17 to 33 % of grain yield enhancement, while 67 to 83% of the increase from previous soybean crop was caused by other rotational effects.