Abstract
Winter rye (Secale cerealeL.) is used as a cover crop because of the weed suppression potential of its mulch. To gain insight into the more effective use of rye as a cover crop we assessed changes in benzoxazinone (BX) levels in rye shoot tissue over the growing season. Four rye varieties were planted in the fall and samples harvested at intervals the following spring. Two different measures of phytotoxic compound content were taken. Seed germination bioassays were used as an estimate of total phytotoxic potential. Dilutions of shoot extracts were tested using two indicator species to compare the relative toxicity of tissue. In addition, BX (DIBOA, DIBOA-glycoside, and BOA) levels were directly determined using gas chromatography. Results showed that rye tissue harvested in March was the most toxic to indicator species, with toxicity decreasing thereafter. Likewise the BX concentration in rye shoot tissue increased early in the season and then decreased over time. Thus, phytotoxicity measured by bioassay and BX levels measured by GC have a similar but not identical temporal profile. The observed decrease in phytotoxic potential and plant BX levels in rye later in the season appears to correlate with the transition from vegetative to reproductive growth.
Highlights
The agricultural use of cover crops has many potential benefits including reduced soil erosion, decreased nutrient runoff, increased soil organic matter, improved soil tilth, the ability to scavenge residual nitrogen, and the suppression of weed growth [1, 2]
Suppression of weed growth is of particular importance to organic growers, due to restrictions in herbicide use [3, 4]
The inhibition of germination and growth of the seedlings were compared to a water control, and the dilution that inhibited growth by 50% (D50) was calculated
Summary
The agricultural use of cover crops has many potential benefits including reduced soil erosion, decreased nutrient runoff, increased soil organic matter, improved soil tilth, the ability to scavenge residual nitrogen, and the suppression of weed growth [1, 2]. Suppression of weed growth is of particular importance to organic growers, due to restrictions in herbicide use [3, 4]. Cover crops suppress weed growth by both physical competition and chemical interference. Chemical interference involves the production and release of allelopathic chemicals, primary and secondary metabolites that are phytotoxic or have growth regulating properties. Many examples of allelopathic chemicals from plants have been described, including sorgoleone from Sorghum Moench spp. [9], juglone from walnut [10], artemisinin from Artemisia L. spp. Many examples of allelopathic chemicals from plants have been described, including sorgoleone from Sorghum Moench spp. [9], juglone from walnut [10], artemisinin from Artemisia L. spp. [6], and the benzoxazinones (BXs) and their metabolites from corn, wheat, and rye [11,12,13,14,15]
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