Stress modification of allelopathy ofHelianthus annuus L. debris on seedling biomass production ofAmaranthus retroflexus L.

When added to soil,Helianthus annuus debris from plants grown under various nutrient stresses in the greenhouse and field had a significant negative effect onAmaranthus retroflexus seedling dry weight production. The regression models for dry weight versus total phenolic compounds and the variation in N, P, and K contents of theHelianthus debris were significant. It was possible to partially simulate debris inhibition ofA. retroflexus seedling dry weight production when chlorogenic acid alone was added to the soil instead ofHelianthus debris. The inhibition ofAmaranthus growth byHelianthus debris and chlorogenic acid was not evident when nutrient solution was applied to the soil.