Quantification of Allelopathic Potential of Sorghum Residues by Novel Indexing of Richards' Function Fitted to Cumulative Cress Seed Germination Curves

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Abstract
The inhibitory activity of aqueous extracts of field-grown sorghum (S. bicolor cv. Bird-a-boo) herbage and roots was quantitatively indexed by 3 aspects of cumulative cress (L. sativum cv. Curlycress) seed germination: the germination onset; weighted mean rate; and final germination percentage. Extract potency was greatest for herbage collected 4 wk after planting but declined sharply thereafter as the plants matured. About 91% of the inhibitory activity obtained from 4-wk-old herbage was in a low MW fraction. Differential effects of herbage and root extracts on cress seed germination suggest that the nature and/or proportion of biologically active substances extractable from these plant parts is dissimilar.