Velvet Bean as a Biological Control of Weeds and Pathogens
This series of projects will answer a few important questions regarding Velvetbean’s effectiveness as a suppressor of some weeds and possibly fungi, as well as Velvetbean’s potential for improving the organic matter content and fertility of soils in two important agricultural areas of Georgia. The data collected and to be presented will also provide a reference for farmers in the Southeast region regarding planting dates and specific effects that can be anticipated when using Velvetbean as a cover crop and as part of a comprehensive crop rotation plan.
One objective of this series of experiments is to determine velvetbean’s weed suppression abilities through field experiments that analyze biomass accumulation and nutrient cycling. This part of the study includes growing Sunn hemp and Velvetbean to collect the previously mentioned data on these somewhat common cover crops from the Fabacea family. This experiment was performed Spring/Summer/Fall of 2002. Lab experiments utilizing the residue from the field experiments will also help to determine velvetbean’s allelopathic affects toward four common southern horticultural weeds (sicklepod, redroot pigweed, crabgrass, and beggarweed). These experiments began in May of 2002 and will be completed by the end of April 2003. Another objective of this series of experiments is to determine any suppression velvetbean may have toward Phytophthora capsici and Rhizoctonia solanii, common southern horticultural fungi. This experiment began in January 2003 and will be completed by the end of May 2003.
A biomass accumulation and nutrient cycling study of Velvetbean (Mucuna sp.) and Sunn hemp (Crotoleria juncea) took place in Watkinsville and in Tifton, GA. In Watkinsville one plot measuring 10’ x 40’ of each cover crop was planted in a block design in April, May, June and July of 2002. The layout was essentially the same in Tifton, except the dimensions of the plots were slightly different. Velvetbean was planted at a rate of 2.5 seed/foot at a depth of 1.5 inches and Sunn hemp was planted at a rate of 9-12 seed/foot (12 lbs./acre) and at a depth of .75 inch using a standard planter set for 30” row widths in Watkinsville and 36” row widths in Tifton. Each plot contained four treatments of different harvest dates (30, 60, 90, and 120 D.A.P.). Fifteen soil core samples were collected per plot at a 4” depth in-row on each harvest date. Four above ground biomass samples per treatment were taken randomly from three linear feet within each plot. Fresh/green weight was recorded, as well, as oven-dried weight after 72 hours in a 150 degree F oven. The previous study was conducted at the USDA experiment station on the Piedmont in Watkinsville, GA as well as at the Coastal Plain USDA experiment station in Tifton, GA. This data is ready for analysis.
The following series of experiments began in May of 2002 and will be concluded May of 2003. Lab experiments are being conducted using the Richards test standards and other experimental methods based on novel indexing of Richards’ function (Lehle and Putnam 1982; Richards 1959). The materials and methods used by Lehle and Putnam in their study of the quantification of the allelopathic potential of sorghum residues are included in this portion of the study (Lehle and Putnam 1982). The materials and methods used in this section will also include those used by Fujii in his experiments to assess the allelopathic activities of Mucuna pruriens (1999). These methods include preparing an aqueous extract of two different parts of the velvet bean plant (the bean and the whole above-ground plant). This will help in the identification of which part of the plant contains the highest concentration of allelopathic compounds particularly effective in the suppression of the Southern weeds used in this portion of the study.
The process just mentioned includes drying each part of the plant at 60 degrees Celsius for 24 hours. Each sample is then ground in a Wiley mill to pass through a 40-mesh screen. An aqueous extract is prepared through different methods of extraction with each ground plant part previously mentioned. Crude extracts of the seed is prepared by stirring 10 g of each ground plant material separately with 100 ml of water overnight at 4 degrees Celsius. Simple aqueous extracts of the whole plant residue from the Watkinsville plots were made using 100 ml distilled water and 1 gram of residue according to Fujii (1999). This mixture is then placed in a mechanical shaker for 2 minutes to complete the transfer of chemicals from the residue to the water. The mixtures are then each filtered through Whatman No. 4 filter paper. Two ml of each of the resulting solutions are placed separately on Whatman No. 1 filter paper set in 9 cm petri dishes. Ten weed seeds (of the same species) are placed in the petri dishes with the saturated filter paper having 4 replications per treatment including distilled water as the control. After 96 hours of incubation in the dark at 25 degrees Celsius the dishes are removed and the number of seeds germinated counted, the hypocotyls and radical growth are also measured (Fujii 1999; Lehle and Putnam 1982). Four types of Southern weeds specifically troublesome in agricultural crops are being used in these experiments. The weeds being tested include Crabgrass spp., Sicklepod, Pigweed spp., and Florida beggarweed (Webster et al. 2001).
The pathogen experiments include growing a strain of P. capsici on a 70:30 cornmeal/sand mixture that had been autoclaved at 121degrees Celsius for 30 minutes. R. solani is being grown on barley oats that had been soaked for 1 hour and then autoclaved at 121 degrees Celsius for 30 minutes two times.
The methods followed for this experiment come from Williams-Woodward et al. (1997). Roughly ten gallons of field soil was collected from the edges of a cotton field on the ARS experiment station in Watkinsville. It was steamed-pasteurized twice at 60 degrees C for 1 hr. at-24 hour intervals. This soil will be used to grow velvetbean in plastic containers (6 x 25 cm; Deepotst™, Steuwe and Sons, Corvallis, OR). Five replications of four treatments will be used: velvetbean inoculated with R. solani, velvetbean inoculated with P. capsici, velvetbean without fungi (control I), and no velvetbean inoculated with each fungi (control II). Roughly 6 W.A.P. the velvetbean above- and below-ground biomass will be evaluated. The velvetbean will then be chopped with scissors and mixed into the soil; which will be placed back into its original pot. Green peppers will then be grown in the soil and residue mixture inoculated with P. capsici and peanuts will be grown in the soil mixture inoculated with R. solani. Green peppers and peanuts will also be planted in the containers for the appropriate controls. At 6 W.A.P. each plant will then be weighed per above ground biomass and root biomass. This experiment will be duplicated simultaneously in two different greenhouses in Athens, GA.
Impacts and Contributions/Outcomes
These studies will provide an idea of the effectiveness of Velvetbean as a suppressor of common southeast horticultural weeds, as well as biomass accumulation and nutrient cycling data on Velvetbean and Sunn hemp as grown in the southeast. Roughly, the most effective planting dates and harvest dates will be determined (through analysis of collected data) for maximum organic matter input, as well as maximum nitrogen input from each cover crop. Weed control was determined visually and noted at each planting date and harvest date. The analyzed data will help determine how each cover crop can most effectively fit into a farming rotation for the southeast. Velvetbean (Mucuna pruriens) shows great promise as a source of L-Dopa (L-3,4-dihidroxyphenylalanine), a precursor of the neurotransmitter dopamine (Fujii 1999). It proves to be effective as a treatment of Parkinson’s disease (Hussein et al. 1997) and continues to be the subject of medical research today (Kumar et al. 1995; Rajendran et al. 1996; Ratnasooriya et al. 1999, Uguru et al. 1997; Yang et al. 2001). Mucuna pruriens is also found in health food stores as a natural remedy for depression. Hence, it appears velvetbean may be an economically viable crop in many ways when grown in rotation with a vegetable crop.
ARS – Southern Piedmont Conservation Research
1420 Experiment Station Road
Watkinsville, GA 30677-0000
Office Phone: 7067695631
UGA – Department of Plant Pathology
160 Plant Science Bldg
Coastal Plain Experiment Station
Tifton, GA 31793
Office Phone: 2293863372