Allelopathic suppression of weed and nitrification by selected cultivars ofSorghum bicolor (L.) moench.

Root exudates of 100 cultivars ofSorghum bicolor L. (Moench) were screened for their ability to inhibit seed germination and seedling growth ofAmaranthus retroflexus L. Exudates of some of the test cultivars were found to inhibit significantly seed germination and/or seedling growth ofA. retroflexus, and most of the inhibitory activity was found in neutral and acetone fractions of root exudates. Testing of aqueous extracts and decaying residues of four selectedSorghum cultivars (two toxic and two nontoxic through root exudation) revealed that all four cultivars significantly reducedA. retroflexus growth and nitrification processes with greater inhibition achieved by the toxic cultivars. This study suggests a potential biological control ofAmaranthus and nitrification by someS. bicolor cultivars.