Allelopathy: Hope or Hype?

Rye has been regularly used as a cover crop/mulch in a number of crop production systems. Rye mulch has been shown to simultaneously increase soil organic matter and reduce erosion. When sufficient biomass is achieved, rye mulch suppresses weeds by serving as a physical barrier to emergence and by inhibiting germination through reduced light transmittance and, purportedly, allelopathy. Many of the studies conducted to assess the alleopathic potential of rye against weeds have used young, green, living, greenhouse-grown tissue as a source of chemical extracts. Few studies have quantified the suppressive potential of rye tissue grown under natural conditions and at a number of development stages; this includes rye that has naturally senesced or has been chemically killed in the field prior to spring crop planting. The usefulness of rye as a 'natural herbicide' would be greatly improved if rye's allelopathic activity is maintained during the peak germination period of summer annuals, like Palmer amaranth. The objective of this study is to evaluate the inhibitory effects of field grown rye, collected throughout the growing season on Palmer amaranth and cotton seed germination.