Oregano green manure for weed suppression in sustainable cotton and corn fields.

A 2 year field experiment was conducted in northern Greece to study the biomass effects of four oregano ( Origanum vulgare) biotypes, used as incorporated green manure, on the emergence and growth of barnyard grass ( Echinochloa crus-galli), bristly foxtail ( Setaria verticillata), common purslane ( Portulaca oleracea), cotton ( Gossypium hirsutum), and corn ( Zea mays). The oregano biotypes were selected on the basis of their high phenolic content. The phytotoxic potential of the oregano biotype extracts also was determined in the laboratory by using a perlite-based bioassay with cotton, corn, and barnyard grass. The bioassays indicated that the germination, root elongation, and fresh weight of cotton, corn, and barnyard grass were reduced by the oregano biotype extracts. In the field, the emergence of common purslane, barnyard grass, and bristly foxtail was reduced by 0-55%, 38-52%, and 43-86%, respectively, in the oregano green manure treatments, as compared with the oregano green manure-free treatments (the controls). At harvest, the cotton lint and corn grain yields in the oregano green manure treatments were 24-88% and 5-16%, respectively, greater than those in the corresponding green manure-free, weedy treatments. These results indicated that when the biomass of the oregano biotypes with a high phenolic content were incorporated into the soil as green manure, they could be used to suppress barnyard grass, bristly foxtail, and common purslane in cotton and corn and consequently to minimize herbicide usage. [ABSTRACT FROM AUTHOR]