- Agronomic: sorghum (milo)
- Pest Management: integrated pest management
- Production Systems: general crop production
The potential use of a warm-season forage grass for controlling peanut pests and for use as livestock feed offers a novel approach to sustainable agriculture. The principal rationale of this research is that switchgrass can be used as a forage grass rotation to enhance sustainability of farms engaged in mixed peanut/cattle production. The long-term goal of this project is to develop profitable and sustainable peanut production systems that will suppress nematodes and other soilborne pathogens, reduce or eliminate pesticide use, and enhance cattle production. Specific objectives are to (1) assess the potential of peanut rotations with switchgrass to suppress infection by root-knot nematodes, aflatoxigenic fungi, and other soilborne pathogens of peanut within integrated peanut and forage-livestock production systems; (2) study the effect of selected warm-season forage grasses on populations of nematodes, aflatoxigenic fungi, and other soilborne pathogens of peanut; (3) evaluate the level and variability of implied net returns from all treatments if adopted on a commercial scale; and (4) determine the impact of switchgrass and other selected warm-season forage grasses on beneficial soil microbial communities.
Field trials were established in 1992 for rotation/production system studies. These three year rotations included continuous peanut, switchgrass-peanut, continuous switchgrass, cotton-peanut, and cotton-cotton-peanut. Peanut and peanut-switchgrass rotations were planted both with and without nematicide (aldicarb) as an industry standard control. Field trials were used to assess the potential of switchgrass rotations to suppress root-knot nematodes and aflatoxigenic fungi, and to assess microbial population shifts with crop rotation under field conditions.
Nematodes were sampled prior to harvest, when populations are highest. Aflatoxigenic fungi were assessed at two week intervals throughout the growing season. Soil microorganisms were sampled at three times during the growing season. Evaluation of shifts in microbial populations and species diversity were used to assess environmental impacts and sustainability of forage grass rotations for disease control. Yield data were collected from field experiments.
A series of microplot experiments were established to more closely investigate the effects of forage grass-peanut, and forage grass-cotton rotations on nematode populations and soil microorganisms. Microplots were sampled for nematodes at planting and before harvest. Methods utilizing nematode eggs in alginate films were developed that allowed for the evaluation of the effects of shifts in soil microbial ecology with cropping system on nematode eggs in microplots.
Enterprise budgets were developed using yield and input data. Enterprise budget computations were made across all treatments and replications. Net return results were analyzed to determine differences in potential business profits. Analyses included business returns for existing producers as well as new entrants. Procedures were used to trace the trade off between return levels to return variability. Results allowed conclusions to be drawn concerning adoption of nematode control strategies by risk averse, risk neutral, risk seeking entrepreneurs.
Measurement and Results
The results of nematode isolations indicate that in field trials, switchgrass and cotton did not support populations of root-knot nematode. Switchgrass supported higher populations of nonparasitic (beneficial) nematodes than cotton. Peanut with no nematicide following two years of switchgrass provided the same nematode control as continuous peanut plus nematicide. Experimental results do not lead to any firm conclusion that switchgrass rotations can minimize invasion of peanut seed by aflatoxigenic fungi. However, these data do support the hypothesis that particular rotation sequences can contribute to minimizing peanut seed invasion by aflatoxigenic fungi, and subsequently minimize aflatoxin contamination of the peanut crop.
Microbial populations in field trials indicate that switchgrass supported lower numbers of rhizosphere fungi than peanut throughout the season, and a distinctly different bacterial microflora compared to continuous peanut and peanut following switchgrass. These shifts in bacterial populations are consistent with previous results where similar shifts resulted in soils being suppressive to one or more pathogens including root-knot nematodes and Sclerotium rolfsii.
Results of microplot studies indicate that switchgrass reduced egg viability and juvenile emergence, increased the number of eggs parasitized by fungi or bacteria, and reduced the number of root-knot nematode juveniles in soil compared to peanut or cotton in microplots. Overall, alginate films containing eggs placed in microplots planted to grasses had fewer viable eggs and more parasitized eggs than films placed in plots with peanut, indicating an altered soil microflora antagonistic to nematode eggs. Significantly fewer J2 hatched out of eggs from films placed in grass plots.
Peanut yield did not differ among treatments in field plots in 1993 or 1994. In 1995 peanut plus nematicide in a one year rotation with switchgrass had significantly higher yield than continuous peanut either with or without nematicide. In 1996 only the continuous peanut treatments both with and without nematicide were planted to peanut. Consequently, no data on the effects of peanut-switchgrass rotation on peanut yield were collected during this year. Economic analysis indicates that in the present situation where farmers can sell quota peanuts at prices that are fixed by the USDA, the farmer would choose to plant half of his land in continuous peanut with nematicide and the rest in two years of cotton followed by additional (nonsubsidized) peanuts. To compare this with switchgrass based rotation, the analysis forced only rotation patterns containing at least one year of switchgrass in the rotation practice. It was observed that the profit was reduced almost 1/3 of the former level. On the other hand, in this situation the farmer used much less chemicals. The other conditions analyzed in this study was with the assumption of complete elimination of the peanut program. When quota was eliminated, farmers would still choose not to plant switchgrass because of lower profit potential. Because farmer places higher utility to profit than environmental amenities, switchgrass was not included in the rotation practice. When switchgrass was forced in the rotation practice with complete quota elimination situation, the farmer decides not to plant any crop.
This project was implemented to assess the efficacy and economic potential of using switchgrass (Panicum virgatum) rotations for the sustained production of peanuts and as a livestock feed source. Peanut production in the Southeast is currently limited by damage from the root-knot nematode, southern root rot, and contamination with aflatoxins. Nematodes often interact synergistically with soilborne pathogens and may increase contamination of peanut seed with aflatoxigenic fungi. Current control options of nematicides for root-knot nematodes and irrigation for aflatoxigenic fungi are effective under some conditions but are not economically practical or may have negative environmental impacts. Shifts in microbial populations and species diversity were employed to assess environmental impacts and sustainability of forage grass rotations for disease control. Results indicate that switchgrass reduced egg viability and juvenile emergence, increased the number of parasitized eggs, and reduced the number of root-knot nematode juveniles in soil compared to peanut or cotton in microplots. In field trials, switchgrass and cotton did not support populations of root-knot nematode. Switchgrass supported higher populations of nonparasitic (nonstylet bearing) nematodes than cotton. Peanut with no nematicide following two years of switchgrass provided the same nematode control as continuous peanut plus nematicide. Switchgrass supported lower numbers of rhizosphere fungi than peanut throughout the season, and a distinctly different bacterial microflora compared to continuous peanut and peanut following switchgrass. Previous crop and aldicarb treatment did not have a consistently significant effect on the incidence of pods infected with Aspergillus, however, pod invasion by A. flavus was highest in plots previously planted to peanut and to which aldicarb had not been applied. Peanut yield did not differ between treatments for either 1993 or 1994. Economic analysis to determine differences in potential business profits indicate that under the present price support system a farmer would choose to plant half of his land in continuous peanut with nematicide application and the rest in two years of cotton followed by one year of additional peanuts (nonsubsidized peanuts) without nematicide. With a switchgrass based rotation containing at least one year of switchgrass, profit was reduced by almost 1/3 of the former level. However, in this situation the farmer used much less chemicals. When quota was eliminated, the model indicated not to plant switchgrass because of lower profit potential. Because farmers place higher utility to profit than environmental amenities, switchgrass was not included in the rotation practice. When switchgrass was forced in the rotation practice with complete quota elimination, the decision is not to plant any crop.