Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/2/2008
Publication Date: 9/21/2008
Citation: Teasdale, J.R., Rice, C.P., Zasada, I.A. 2008. Role and persistence of rye allelopathic activity in soil [abstract]. 5th World Congress on Allelopathy. 176:88-89.
Technical Abstract: Many extracts and compounds isolated from winter annual cover crops have been demonstrated to have allelopathic activity. These compounds can contribute to weed suppression when cover crops are terminated before planting a cash crop. Although cover crop extracts can exhibit allelopathic activity in laboratory assays, they would be expected to have less activity and persistence in a soil environment. Literature suggests that, following cover crop termination, residues become less toxic as they decompose over a period of several weeks. An experiment was conducted to determine the allelopathic activity and persistence of rye (Secale cereale L.) after cover crop termination in 2006 and 2007 at two sites near Beltsville, MD. Rye in a late vegetative stage was killed by an application of paraquat and residue either shallowly incorporated or retained on the soil surface without tillage. The annual broadleaf weed, smooth pigweed (Amaranthus hybridus L.), and lettuce (Lactuca sativa L. ‘Great Lakes’) were planted into the incorporated rye, the no-tillage rye, or a control (with tillage similar to the incorporated rye treatment) immediately following and at approximately weekly intervals after tillage. Soil to a 10 cm depth was removed from each treatment at the same time that test species were planted in the field and assayed in a hoophouse pot experiment using the same test species. Soil was also collected for determination of benzoxazinoid concentrations in soil with LC-MS/MS at the same weekly intervals. Results of the field assay demonstrated a high level of suppression of both test species when planted immediately after rye termination (pigweed and lettuce plant mass was reduced 84 and 89%, respectively, by incorporated rye, and plant mass of both species was reduced 98% by surface rye residue compared to control plots). Suppression declined with subsequent plantings to less than 20% after approximately three weeks for incorporated rye and approximately five weeks for surface rye. Results of the hoophouse assay demonstrated a moderate suppression of both test species by soil from rye incorporated immediately after planting (pigweed and lettuce mass were reduced by 37 and 49%, respectively) but this suppression declined to less than 20% within one week after rye termination. Soil from no-tillage rye had no suppressive activity in the hoophouse assay. These results suggest that release of allelopathic compounds accounted for at least half of the field suppression observed with incorporated rye but this effect was short-lived. Allelopathy apparently made no contribution to field suppression by surface rye residue.