Allelopathy of sorghum on wheat under several tillage systems

Allelopathy by grain sorghum [Sorghum bicolor (L.) Moench] frequently harms wheat (Triticum aestivum L.) when the crops are grown in rotation. Respons es of seven wheat cultivars to different methods of tilling sorghum stover were investigated to determine if the problem might be remedied by genetic resistance or improved management of the stover. Field trials on Kahola sil t foam soil (fine-silty, mixed mesic Cumulic Hapludolls) compared effects o f fallow, tilled sorghum stover, and no-till sorghum stover during the firs t season and the same treatments plus no-till millet [Pennisetum glaucum (L .) R. Br.] stover the second season. The seven wheat cultivars were planted after the sorghum and millet were harvested and tilled, and their emergenc e, stand density, and yield components were measured. Tilled sorghum residu e often delayed development of the following wheat crop but did not affect grain yields, probably because allelopathic compounds degraded in the soil. No-till sorghum stover had little effect on stand establishment but freque ntly reduced grain yields of wheat, possibly because allelopathic compounds leached slowly. Wheat grain yields (means of all seven cultivars) were 3.3 , 2.8, and 2.3 Mg/ha in fallow, tilled sorghum residue, and no-till sorghum residue, respectively, during 2 yr and 3.1 Mg/ha in no-till millet residue in the second year. Selection of resistant wheat cultivars is probably imp ractical, because differences were small and inconsistent. However, if eros ion of soil is not a concern, allelopathy might be reduced by prompt tillag e and other practices that promote rapid decomposition of sorghum stover.