Allelopathic potential of a biculture cover cropping system utilizing Fabaceae and Brassicaceae cover crops

2007 Annual Report for OS07-037

Project Type: On-Farm Research
Funds awarded in 2007: $12,840.00
Projected End Date: 12/31/2009
Region: Southern
State: Virginia
Principal Investigator:
Janet Spencer
Virginia Cooperative Extension

Allelopathic potential of a biculture cover cropping system utilizing Fabaceae and Brassicaceae cover crops


This research investigated effects on individual cover crops and weed suppression in both monoculture and biculture cover cropping systems. The four systems were as follows: 1. Bare-ground control, 2. monoculture of purple vetch, 3. monoculture of oilseed radish, and 4. biculture of 50% purple radish and 50% oilseed radish. Initial results from this study indicate that a biculture production system involving a brassica (oilseed radish) and legume (purple vetch) cover crop may not be a viable system. When purple vetch was planted in a monoculture, percent coverage totaled 32.5%, which is significantly higher than 11.88% coverage when planted in the biculture system with oilseed radish. Subsequently, percent coverage of oilseed radish in a monoculture compared to the biculture with purple vetch was not significantly different, totaling 78.13% and 75.00%, respectively.
When percent coverage of weeds was analyzed in each cropping system, ones that included oilseed radish in the planting showed significantly lower percentages of weed coverage. The monoculture of oilseed radish resulted in 14.75% weed coverage while the biculture planting resulted in 19.25% weed coverage. These values were significantly different when compared to the monoculture of purple vetch and the bare-ground control. The monoculture of purple vetch resulted in 50.13% weed coverage, while the bare-ground control showed weed coverage of 50.75%. These two values were not significantly different from one another.

Objectives/Performance Targets

  • Determine compatibility and weed suppression of brassica and legume cover crops in a biculture production system.

    Determine the allelopathic effects of cover crops on tomato yields when transplanted into brassica and legume cover crop residues.


Cover crop plots were planted in Dinwiddie County (Adams’ Farm) on August 13, 2007 and at the Tidewater AREC on September 11, 2007. Prior to planting, soil samples were taken from individual treatment plots at each location and evaluated for basic nutrients and percent organic matter. Data was collected on September 28th (Tidewater AREC) and October 1st (Dinwiddie County). Data collection was delayed approximately two weeks in Dinwiddie due to severe drought conditions and its impact on germination of the cover crops. Data collection consisted of ground coverage percentages for each of the cover crops and weeds.
In May 2008, tomatoes will be transplanted into the cover crop residues in each cover cropping system. Plants will be maintained as outlined in the 2008 Virginia Commercial Vegetable Production Recommendations guide. Data will be collected on yield and evaluated for each system. In August 2008, all cover cropping systems will be planted again at the Tidewater AREC and in Dinwiddie County as previously done in 2007. Data collection will be similar to methods performed in 2007 and tomatoes will again be transplanted into residues to determine effects on yield.

Impacts and Contributions/Outcomes

During the tomato growing season, two field days will be conducted to disseminate data concerning biculture cover cropping systems and possible effects on subsequent cash crops. Information obtained from this study will be used to generate Cooperative Extension fact sheets and grower/Extension talks to relay the benefits of cover crops and possible effects of biculture cover cropping systems.


Mike Parrish

[email protected]
Virginia Cooperative Extension
P.O. Box 399
Dinwiddie, VA 23841-0399
Office Phone: 8044694514