Allelopathy of Sorghum on Wheat under Several Tillage Systems

Abstract

Allelopathy by grain sorghum [Sorghum bicolor (L.) Moench] frequently harms wheat (Triticum aestivum L.) when the crops are grown in rotation. Responses 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 silt loam soil (fine‐silty, mixed mesic Cumulic Hapludolls) compared effects of fallow, tilled sorghum stover, and no‐till sorghum stover during the first 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 emergence, stand density, and yield components were measured. Tilled sorghum residue 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 frequently 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 impractical, because differences were small and inconsistent. However, if erosion of soil is not a concern, allelopathy might be reduced by prompt tillage and other practices that promote rapid decomposition of sorghum stover.