Canola Emergence and Early Growth Were Not Affected by Allelopathic Properties of Wheat Residue

Abstract

Core Ideas: Negative impacts of fresh wheat residue on canola were demonstrated in the lab. No negative impacts were observed in pot conditions that mimicked the field. Results were generally consistent across 15 wheat varieties and 2 soils. Negative impacts of wheat residue reported on canola are likely physical impacts. Wheat (Triticum aestivum L.) has been studied for its residual chemical effects on other crop plants, which are often cultivar-specific, but its effects on canola (Brassica napus L.), a crop increasingly rotated with wheat, are less understood. Because canola production is spreading to new areas, including the US Southern Great Plains, our objective was to evaluate the potential for allelopathic properties of wheat residue from regional cultivars to negatively impact emergence and early growth of canola. A laboratory study was conducted, establishing a baseline for potential allelopathic effects, and an outdoor pot study was conducted, designed to test for these effects in conditions mimicking field conditions and crop management (e.g., residue weathered on the soil surface for the summer to simulate fallow). In the laboratory, with exposure to fresh wheat residue extracts, canola germination was delayed, but persistent, concentration-dependent negative effects on radicle elongation were observed, similar to other reported results. In the pot studies, wheat residue did not affect canola emergence, with minimal variation among 15 wheat cultivars tested in two soils, and early growth increased by an average of 23% with residue treatment. The canola emergence and early growth results indicated an absence of allelopathy at planting and the presence of growth-promoting factors following wheat residue application. Together, these studies indicate that allelopathic properties of wheat residue can negatively impact canola in laboratory conditions, but suggests these effects are not likely to be realized under typical field conditions. Negative impacts of wheat residue on canola, which have been reported, are likely physical in nature.