Abstract
Cover crops can provide a variety of benefits to an agricultural system: weed suppression, soil quality improvement, and soil water infiltration. Although there is ample research documenting weed suppression from cover crops, the mechanics of the suppression are not implicitly understood. Along with the aforementioned positive attributes, negative allelopathic effects on row crops planted into cover crop systems have been documented. The objective of this study was to evaluate the allelopathic potential of certain cover crop species on soybean (Glycine max L.) and goosegrass (Eleusine indica L.) germination and early seedling growth under controlled environments in petri dish and pot experiments. Leachates from above-ground biomass of five cover crop species, wheat (Triticum aestivum L.), cereal rye (Secale cereale), hairy vetch (Vicia villosa), crimson clover (Trifolium incarnatum L.), and canola (Brassica napus L.), from two locations (East and Middle Tennessee) were extracted and applied at 0 (water) and 50 v/v. In experiment I, both soybean and goosegrass seeds were examined, and, in experiment II, only soybean seeds were examined under the application of cover crop leachates. Most cover crop leachates from both locations significantly reduced the soybean seedling root length (p < 0.01). Overall, the application of canola extract (East Tennessee) suppressed soybean seed germination the most (28%) compared to deionized water. For goosegrass, the wheat cover crop leachate significantly reduced seedling root length (p < 0.01). In experiment II, the soybean root nodulation was significantly increased with the wheat extract treatment compared to deionized water. While the results indicate that the location and environment may change cover crop species allelopathic potential, the wheat cover crop leachate had the most potent allelopathic impact on goosegrass germination and growth; however, had the lowest observed adverse effect on our tested row crop, soybean.
Highlights
The adoption of conservative farming practices, such as no-tilling systems, has increased the utilization of cover crops in agronomic systems [1]
Research has documented negative allelopathic effects on row crops planted into cover crop systems [5,6], the suppression of seedling growth on succeeding cash crops [1,7,8]
For East Tennessee (ET), germination percentage was numerically lower for cover crop treatments compared to the check, but not statistically significant (Figure 1a)
Summary
The adoption of conservative farming practices, such as no-tilling systems, has increased the utilization of cover crops in agronomic systems [1]. Cover crops offer many potential benefits to a production field, including weed suppression, soil quality improvement, and soil water infiltration [2,3]. These known benefits are only part of the equation; naturally produced allelochemicals from cover crops could suppress herbicide-resistant weeds and support a sustainable agricultural production system [4]. Research has documented negative allelopathic effects on row crops planted into cover crop systems [5,6], the suppression of seedling growth on succeeding cash crops [1,7,8]. Xuan et al [9] reported that the most common pathways for allelochemicals to be introduced in the soil are through leaching, volatilization, root exudation, and the death and decay of the fallen plant parts via biotic or abiotic means
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