Submitted to: Revista Agropecuaria Brasileira
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/1999
Publication Date: N/A
Interpretive Summary: Allelopathy is the process by which some plants have a harmful effect on other plants through the release of a chemical compound or compounds into the environment. This process may be partially responsible for the observed suppression of some weed species by crop residue. Ferulic acid, catechol, caffeic acid and salicilic acid are some of the phenolic compounds known to be allelopathic to giant foxtail. Rates of these compounds equal to the amounts available in a wheat straw residue of 12 Mg/ha did not reduce foxtail germination in the field as might be expected. Giant foxtail seed germinated better in soil than in petri-dish experiments, suggesting that adsorption plays an important role in the performance of these phenolic compounds in allelopathy. Germination experiments using giant foxtail without soil showed the allelopathic potential of the tested phenolics to be ferulic acid>catechol>salicilic acid>caffeic acid. The results suggest that the role of phenolic compound in allelopathy is strongly influence by environmental and other factors. Adsosrption of these compounds by soils makes them less available to effect the germinating seeds. The allelopathic effects may be further limited by the time required for the plant residues to decay. Germinating seed must be located in close proximity to the allelochemical in order for suppresion to occur. The impact of allelopathy is a complex interaction of allelochemicals, crop residues, soils, and other environmental factors. Simple measuremet of allelochemical levels, in crop residues, will not predict allelopathy.
Technical Abstract: Allelopathy could be used to reduce weed infestations, but adsorption of allelochemicals to soil can reduce its effects in agro-ecosystems. The objectives of this work were to study the effect of caffeic, ferulic, and salicilic acids, and catechol on Setaria faberi (SETFA) germination in petri-dish and soil bioassays, and to determine the adsorption of these phenolic compounds to a silt clay loam soil. Petri-dish experiments using SETFA as the indicator species showed the allelopathic potential of the phenolics tested was: ferulic acid > salicilic acid > caffeic acid. Caffeic acid, up to 27 mM, did not affect SETFA germination. SETFA germinated better in soils than in petri-dish experiments, suggesting that adsorption plays an important role on the performance of the phenolic acids. Adsorption of the phenolics to soil ranged from 10 to 40 percent of the applied concentration. Caffeic acid and catechol had more affinity with the soil than salicilic and ferulic acids. The rate of these phenolics in 12 t/ha of wheat straw is not enough to reduce SETFA germination in the field. These results indicate that the allelochemical activity may be limited by their adsorption to the soil.