Submitted to: Allelopathy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/25/2009
Publication Date: 9/8/2009
Citation: Kremer, R.J., Moncef, B. 2009. Allelopathic Plants. Hordeum vulgare L. Allelopathy Journal. 24(2):225-242. Interpretive Summary: Many plants release chemical substances from roots or, less frequently, from other components (leaves, pollen) that inhibit the growth of neighboring plants, a condition known as “allelopathy.” The use of allelopathic crops as a technique to inhibit growth of weeds that infest fields has been pursued for many years in sustainable agriculture as a natural form of weed management requiring little or no herbicides, the conventional chemical means of controlling weeds. Barley, widely known as a cereal grain crop utilized as malt for brewing, specialty foods, and livestock feed, also plays an important role as a cover crop for soil conservation with coincident ability to suppress weed growth due to allelopathic effects. Allelopathic effects of barley have been known since the early 1900’s but recognition of the allelochemicals responsible for its allelopathy has only occurred within the past 50 years. We reviewed the literature to provide an up-to-date perspective on the allelopathic nature of barley and to suggest ways in which barley might be used more effectively through innovative integration in cropping systems and by selection of allelopathic varieties. Less than 20 allelochemicals involved in expression of barley allelopthy have been identified; contents and composition of these substances vary widely among barley varieties. Little research addresses recommendations of specific barley varieties for sustainable weed management. We suggest that genetic selection of allelopathic varieties patterned after similar efforts for allelopathic rye, oats, and rice, as well as combining barley cover cropping with other biological control approaches (i.e., beneficial weed-attacking microbes) will strengthen adaptation of barley as an effective weed-suppressive cover crop. The conclusions of this study are important to extension personnel, weed scientists, crop breeders, and farmers because they show the potential for barley as an allelopathic crop, providing an effective alternative to other cover crops that might not be available or too expensive to include in some crop production enterprises.
Technical Abstract: Barley (Hordeum vulgare L.) is an annual cereal and one of the first agricultural crops to be domesticated. It is a versatile crop and is broadly used as a food grain for human consumption, malt source for brewing, and feed grain for livestock. On-farm crop uses include pasture, a hay and silage source, a nurse crop for establishing other crops, and in soil conservation or weed-suppression as a cover crop. Because barley integrated with other crops is effective in inhibiting weed growth, we address the role of allelopathy involved in these associations. Effects of barley on growth of other crops, weeds, and autoxicity among cultivars result primarily from allelopathy mediated by allelochemicals released from plant components and/or exuded from living roots. A limited number of allelochemicals are identified that contribute to the allelopathic effectiveness of barley. High allelopathic effectiveness of barley has resulted in wide adoption as a cover crop in sustainable agricultural systems for weed management. Because allelopathic effectiveness varies among barley cultivars, selection programs might improve allelopathic potential of cultivars used for weed management. Allelochemicals in barley may be candidates for natural herbicides and innovative approaches for integrating barley cover cropping with other cultural practices may improve sustainable or biologically-based weed management.