Warm-Season Forage Grasses as Rotations for Sustaining Profitable Peanut Production

Final Report for LS93-051

Project Type: Research and Education
Funds awarded in 1993: $183,000.00
Projected End Date: 12/31/1996
Matching Non-Federal Funds: $48,500.00
Region: Southern
State: Alabama
Principal Investigator:
Rodrigo Rodriguez-Kabana
Auburn University, Plant Pathology
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Project Information

Abstract:
Non-Technical Summary

Objectives

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.

Methods

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.

Technical Report

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.

Introduction:

On an annual basis, 1.5 million acres of peanuts are harvested in the U.S., and over 1.3 billion pounds are consumed. The crop value exceeds $1 billion annually, and approximately 65% of domestically produced peanuts are grown in the southeastern U.S. Peanuts are particularly vulnerable to soilborne pests because their seed matures underground. Pests that cause economic losses to producers in this region include root-knot nematodes (Meloidogyne arenaria and M. hapla), southern stem rot (caused by the fungus Sclerotium rolfsii), and fungi that produce aflatoxins.

Annual yield losses due to root-knot nematodes in Alabama have been estimated at slightly greater than 5% of the state's total peanut crop (Sturgeon, 1986). With southern stem rot, Sturgeon (1986) estimated annual losses at 5 to 10% of the crop value. In addition, S. rolfsii and nematodes may interact synergistically in damaging peanuts and reducing yields (Culbreath et al, 1991). Aspergillus flavus and A. parasiticus are closely related species of aflatoxigenic fungi, producing the highly carcinogenic compounds called aflatoxins (Diener et al, 1982). These fungi are ubiquitous in peanut soils and are found on peanut plants throughout most growing seasons (Diener et al, 1987). Seed invasion by aflatoxigenic fungi is aggravated by pod damage resulting from natural cracking, soilborne insect feeding (Widstrom, 1979; Lynch and Wilson, 1991; Bowen and Mack, 1991), and nematode feeding (Jackson and Minton, 1968; Minton et al, 1969; Minton and Jackson, 1969). Root-knot nematodes, S. rolfsii, and aflatoxigenic fungi constitute an interactive group of pests which combine to limit profitability and sustainability of peanut production in the southeastern U.S.

Other than recommendations for irrigation, there are currently no efficacious controls for reducing aflatoxin contamination of peanuts in the southeastern U.S. Fumigants, although very effective for controlling nematodes, are no longer considered the best means of control due to their cost, safety considerations, and negative environmental impact. Crop rotation offers a means of managing pest problems without negative impact and offers the potential for integration with livestock production, depending on the crop selected for use in rotations.

Switchgrass is a native forage species that is emerging as both an outstanding forage crop and an energy crop. A 3-yr grazing experiment indicated that switchgrass is capable of producing over 1,000 kg/ha of animal weight gain per year with average daily gains of 0.9 kg (Burns et al, 1984). In addition, switchgrass has been identified as a model species to be developed as an energy crop for biomass production and conversion to ethanol. Other advantages of switchgrass include, low fertilizer requirements, wide adaptation to different soils, good soil conservation properties, a deep root system, a long growing season, and excellent wildlife habitat.

Preliminary work at Auburn University has demonstrated that switchgrass has potential for control of phytopathogenic nematodes. In a screen of 12 warm-season grasses, two varieties of switchgrass significantly reduced soil populations of juveniles and subsequent populations on soybean and squash of soybean cyst and root-knot nematodes, respectively. Numbers of root-knot juveniles per squash root system were reduced from 155 for the squash control to 0 with both switchgrass varieties. The same two switchgrass varieties have demonstrated efficacy in reducing nematode populations in microplot studies conducted in 1992. Based on these results, switchgrass may be considered as antagonistic to nematodes.

Crop rotations have been examined as economically viable controls for nematodes on peanut in Alabama since 1984. Rotations with corn, sorghum, cotton, and soybean demonstrated reduced levels of nematode damage to subsequent peanut crops (Rodriguez-Kabana and Touchton, 1984; Rodriguez-Kabana et al, 1991a & 1991b), but have not been widely adapted because they are not economically beneficial throughout the southeastern U.S. Recently, studies have included forage grasses in a long-term effort to identify rotations which can reduce nematode damage on peanut while serving as an economic livestock feed source. Following two years growth of bahiagrass, numbers of M. arenaria juveniles were significantly reduced, the incidence of southern blight was lowered, and average yields increased 36%, compared to nonrotated peanuts (Rodriguez-Kábana et al., 1991c). Bahiagrass is used in the southeastern U.S. as a forage grass; however, problems with stand establishment and severely limited forage quality restrict its potential for cattle production.

To ensure long-term sustainability of a proposed alternative agriculture system, it is desirable to begin assessment of environmental impacts early in the development cycle. We propose, in the 2-yr project period, to focus environmental impact studies on determining how switchgrass affects microbial communities associated with soil, roots, and peanut pods. Specifically, we will examine how treatments affect species diversity (total number of species present) and species richness (predominance of individual species). The rationale for focussing on this aspect of environmental impact is two-fold. First, shifts in microbial populations and species diversity represent a sensitive system for detecting environmental impacts. Second, identification of specific microbial taxa which predominate in the presence of switchgrass could lead to their eventual use as biological agents in integrated efforts for enhancing plant growth (Kloepper et al., 1991) or controlling diseases (Kloepper, 1993). Other aspects of environmental impact are beyond the scope of this preliminary two-year study, and these can be addressed in future developmental research with the optimized rotation system developed here.

The long-term goal of this project was 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. The specific objectives were to (1) assess the potential of peanut rotations with switchgrass to suppress infection by aflatoxigenic fungi, root-knot nematodes, 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 aflatoxigenic fungi, nematodes, 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 the species diversity and species richness of indigenous soil, rhizosphere, and geocarposphere microbial communities. The results of this study provide a better understanding of the use of switchgrass as a rotation crop that is economically feasible, provides control of soilborne pathogens, and enhances beneficial microorganisms to sustain crop and livestock production.

Research

Materials and methods:

Objective 1. Assess the potential of peanut rotations with switchgrass to suppress infection by aflatoxigenic fungi, root-knot nematodes, and other soilborne pathogens of peanut within integrated peanut and forage-livestock production systems.

In 1992, fields were planted to peanut and switchgrass for rotation/production system studies. These production systems consisted of continuous peanut, one year of switchgrass followed by peanut, two years of switchgrass followed by peanut, one year of cotton followed by peanut, and two years of cotton followed by peanut. Peanuts planted in rotation with switchgrass either received (P+) or did not receive (P-) aldicarb at planting. During the growing season, peanut crops in different production systems were monitored for relative population levels of organisms of interest.

Nematodes were extracted from soil samples using the `salad bowl' incubation method (Rodríguez-Kábana and Pope, 1981). Soil samples (100 cubic centimeters) were collected for evaluation of parasitic and non-parasitic (non-stylet bearing) nematode populations. Populations were expressed as nematodes/100 cubic centimeters of soil.

Incidence of aflatoxigenic fungi on pegs and pods was monitored every other week. Up to five plants per plot were dug; pegs and developing pods were removed from plants, returned to lab, surface sterilized, moistened with sterile saline solution and incubated at 32 degrees C for 3 days, after which A. flavus-type fungi were counted. These incubation conditions favor the growth of A. flavus which are easily distinguished from other fungi by their conidial morphology and color. In addition, peanut samples taken at harvest were evaluated for nematode damage, aflatoxigenic fungal incidence and aflatoxins. Populations of these organisms in the production systems were compared.

Objective 2. Study the effect of selected warm-season forage grasses on populations of aflatoxigenic fungi, nematodes, And other soilborne pathogens of peanut.

Microplots were established in 1992 with various warm-season forage grasses, including two varieties of switchgrass, crabgrass and eastern gammagrass. Peanuts were planted in these microplots in 1993 and monitored for nematode population levels. Microplot experiments were performed to evaluate the effects of several annual warm-season forage grasses on nematode populations and yield of eggplant. Switchgrass (Panicum virgatum) cultivars `Alamo' and `Cave-in-Rock', `Red River' crabgrass (Digitaria sanguinalis), and `Eastern' gammagrass (Tripsacum dactyloides) were used in rotations with hairy vetch (Vicia villosa), annual ryegrass (Lolium spp.), and eggplant (Solanum melongena) with and without nematicide. Numbers of root-knot juveniles (Meloidogyne arenaria), spiral nematode (Helicotylenchus dihystera), and nonstylet-bearing nematodes were counted following each crop. Eggplant yield was evaluated throughout the final cropping sequence.

A second series of microplot experiments were implemented in the spring of 1994,
in order to more closely study microbial interactions in rotations. Four microplot rotation experiments were implemented consisting of rotations ‘Alamo’ switchgrass and cotton, ‘Alamo’ switchgrass and peanut, ‘Cave-in-rock’ switchgrass and cotton, and ‘Eastern’ gammagrass and cotton. Peanut experiments were performed in soil from a peanut growing region, and cotton experiments were performed in soil from a cotton growing region. All treatments in each experiment were replicated 8 times and arranged in randomized complete blocks.

A method was developed for utilizing alginate films to deliver inoculum into soil and evaluate microbial antagonistic activity against nematode eggs. Eggs of Meloidogyne incognita were harvested from galled tomato roots (Lycopersicon esculentum), surface disinfested, suspended in 2% (w/v) aqueous sodium alginate, and applied to 2.5x5.0 cm polyvinyl chloride coated fiberglass screens (1.5 square mm mesh size) at a uniform thickness of 0.5 mm. The alginate solution was gelled by dipping in 0.25 M CaCl2. Films containing eggs were observed in vitro and egg development was evaluated.

Objective 3. Evaluate the level and variability of implied net returns from an treatments if adopted on a commercial scale.

Economic analyses included business returns for existing producers as well as new entrants. Results allowed conclusions to be drawn concerning adoption of nematode control strategies by risk averse, risk neutral, risk seeking entrepreneurs. To evaluate the level and variability of implied net returns, enterprises budgets were developed to represent production of peanuts on a commercial scale following practices associated with each treatment included in this study. Enterprise budgets contain the following costs and returns data: (1) gross receipts representing expected price multiplied by yield; (2) preharvest costs consisting of hired labor, fertilizer, lime, herbicides, fungicides, insecticides, variable tractor and machinery, and interest on operating capital; (3) harvest variable cost consisting of hired labor, variable tractor and machinery, and hauling; (4) income above variable cost; (5) fixed costs of machinery and equipment that do not vary directly with annual production decisions, namely depreciation, interest, insurance, and certain repair cost; (6) total cost; (7) net returns to land, fixed labor, and management.

Enterprise budget computations were made across all treatments and replications. Net return results were analyzed using analysis of variance techniques to discover statistically significant differences in potential business profits. Analyses includes business returns for existing producers as well as new entrants.

Data source for this analysis includes an experiment conducted at the Wiregrass substation at Headland, Alabama in 1992 - 1994. `Florunner' peanut, `Alamo' switchgrass and `Deltapine 90' cotton was incorporated in different rotation systems. Eight different rotation practices for three years were compared. The rotation pattern includes present scenario and four other alternatives with the inclusion of switchgrass. The rotation systems included in this analysis are:

Peanut+Peanut+Peanut (PPP)
Peanut-+Peanut-+Peanut- (P-P-P-)
Switchgrass+Peanut-+Switchgrass (SGP-SG)
Switchgrass+Peanut+Switchgrass (SGPSG)
Switchgrass+Switchgrass+Peanut- (SGSGP-)
Switchgrass+Switchgrass+Peanut (SGSGP)
Cotton+Peanut+Cotton (CTP-CT)
Cotton+Cotton+Peanut (CTCTP-)

Where peanut and peanut- denotes the peanut treated with temik or not, respectively. The first crop indicates the crop planted in the first year (1992) of rotation. This crop was followed by another crop in the same field.

Marketing of quota peanut is restricted for a particular farm and is determined by the USDA based on past peanut plantation history of that particular farm. Additional peanuts are any quantity beyond the allotted quota. Farmers do market additional peanut in competitive market at a lower price (less than one-half) compared to the quota price. In this analysis, quota amount is 0.75 of average yield of peanuts cultivated on last three years. Quota price is $700 per ton and additionals sold at $300 per ton.

For risk neutral analysis, the following linear programming model was used:
Max~ PSI=sum from{ i=1} to{ 5} P_i Y_i - sum from {j=1} to 4 C_i -~ O~V-~H

Subject to:
Total Full time Labor Supply each year: Lp+Lct+Lsg <= 2
Quota (tons): Q1=Q2=Q3 <= 200
Cotton Base (acreage): CT1=CT2=CT3 <= 200
Total land supply: Dsg,i+Dp,i+Dct,i <= 400 Where, ψ is total income above variable cost. P is vector of price, Y is vector of output, OV is cost other then chemicals, H is hired labor, I denotes the year and varies from 1 to 3. All decision variables and constraints are positive.

Farmers may make production and input decisions in semi-competitive product markets and competitive input markets considering two objectives: maximizing the profit and minimizing the use of chemicals. The problem is also analyzed to see the policy effect of peanut quota elimination on the profit potential of the farmer and hence adaptation of switchgrass. This analysis is based on micro economic approach and is used to derive the macro economic solution.

Objective 4. Determine the impact of switchgrass and other selected warm-season forage grasses on the indigenous soil, rhizosphere, and geocarposphere microbial communities.

The impact of the warm season grasses on microbial communities was studied in the field and microplot experiments described in objectives 1 & 2. Plant and soil samples were collected three times during the growing season. Plants were taken at random from each treatment and replication. Roots and pods with attached soil were placed in plastic bags and transported in a cooler to the laboratory for processing within 24 hr. In the laboratory, samples were separated into root free soil, rhizosphere soil, and geocarposphere soil. Samples were weighed and used for two analyses: determination of total bacterial population densities and identification of species and evaluation of fungal populations. Identifications will then be used to calculate species diversity (number of species present) and species richness (predominance of individual species).

Population densities of total bacteria were determined by dilution plating onto media with differing nutrient status (5% tryptic soy agar [TSA] and full-strength TSA) to allow detection of obligate oligotrophs. Identification of bacteria in samples from the main treatments were conducted by fatty acid analysis using GC analysis of fatty acid methyl esters coupled with the Microbial ID software package of MIDI (Newark, Delaware). This analysis results in identification to species of bacteria based on comparison of fatty acid methyl ester profiles of unknowns to library collections. The identifications will be compiled to express species diversity and species richness of each treatment.

Random samples of 35 bacterial colonies, as determined by rarefraction analysis (Hurlbert, 1971), were taken from 5% TSA plates of root and pod samples. Each isolate was purified prior to extraction of fatty acids (Sasser, 1990). After extraction samples were stored at -20 C until analysis with a Hewlett-Packard gas chromatograph and the Sherlock Microbial Identification System Software (MIDI). Isolates were identified and this data was used to estimate genera richness, evenness, and diversity indices. These indices were used to determine if there were differences in the bacterial community structure among rotations. Genera richness was determined by direct counts of the numbers of genera identified in each sample. The total number of genera as well as number of isolates of each genus were used to determine genera evenness (relative abundance of genera) and diversity (a function of genera richness and abundance). Hill’s modifications, N1 and N2, of Shannon’s and Simpson’s indices, respectively, were used as estimators of diversity, and evenness using Hill’s evenness index (Hill, 1973; Ludwig and Reynolds, 1988).

Research results and discussion:

Objective 1. Assess the potential of peanut rotations with switchgrass to suppress infection by aflatoxigenic fungi, root-knot nematodes, and other soilborne pathogens of peanut within integrated peanut and forage-livestock production systems.

Previous crop and aldicarb treatment did not have a consistently significant effect on the incidence of pegs infected with A. flavus (Table 1). One exception was 5 September when pegs collected from plots which had been treated with aldicarb had significantly more (P=0.06) A. flavus infection than those from plots not treated with aldicarb. By September, more than 100 days after planting, pegs that are still being produced by peanut plants would not be contributing to yield. Therefore, these data need to be interpreted with extreme care.

Previous crop and aldicarb treatment did not have a consistently significant effect on the incidence of pods infected with A. flavus (Table 2). One exception was on 24 August when pods collected from peanut-peanut rotations, without aldicarb treatment had significantly more (P=0.06) A. flavus infection than those from other rotation. On 5 September, A. flavus was only detected in developing pods from plots not treated with aldicarb (Table 2). Variation among data from each plot was high, however, so this was not a significant effect (P<0.10). Areas under the curves of data describing pod invasion by A. flavus were highest from plots previously planted to peanut and to which aldicarb had not been applied (Table 3). These results do not lead to any firm conclusion that switchgrass rotations can minimize A. flavus activity and fungal invasion of peanut seed. 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. Objective 2. Study the effect of selected warm-season forage grasses on populations of aflatoxigenic fungi, nematodes, And other soilborne pathogens of peanut. All warm-season grasses tested reduced populations of parasitic nematodes but did not reduce numbers of nonparasitic nematodes. Eggplant yield was highest with nematicide following 2 plantings of warm-season grass and 1 planting of ryegrass in all experiments except gammagrass. Yield of eggplant without nematicide was consistently better following 2 plantings of warm-season forage grass compared to eggplant without nematicide following only 1 planting of grass. Alginate films (Rodríguez-Kábana, et al., 1994) containing nematode eggs were used in microplot experiments to assess the effects of switchgrass (Panicum virgatum) and gammagrass (Tripsacum dactyloides) on egg viability, egg parasitism, and emergence of Meloidogyne incognita juveniles. Both switchgrass and gammagrass reduced egg viability and juvenile emergence (Fig. 1), increased the number of parasitized eggs (Fig. 2), and reduced the number of M. incognita juveniles in soil compared to peanut or cotton. In field trials, switchgrass and cotton did not support populations of M. arenaria. Switchgrass supported higher populations of nonparasitic nematodes than cotton (Fig. 3). Peanut with no nematicide following two years of switchgrass provided the same nematode control as continuous peanut plus nematicide. Overall, films placed in microplots planted to grasses had fewer viable eggs and more parasitized eggs indicating an altered soil microflora antagonistic to nematode eggs. Significantly fewer J2 hatched out of eggs from films placed in grass plots. Objective 3. Evaluate the level and variability of implied net returns from an treatments if adopted on a commercial scale. Eight different enterprise rotations as mentioned before were analyzed for their profit potential and extent of environmental degradation caused by crop production. The analyses were done in peanut based rotation systems. Since Congress is currently considering the elimination of the peanut quota system granted to the farmer, this includes analyses with and without the peanut program. The result of this analyses is shown in Table 4 (see also the detailed economic analysis included with this report). The first analysis is the present situation where farmers can sell quota peanuts at prices that are fixed by the USDA. In this situation, the farmer chose 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 still chose 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. Objective 4. Determine the impact of switchgrass and other selected warm-season forage grasses on the indigenous soil, rhizosphere, and geocarposphere microbial communities. It is hypothesized that the rhizosphere microflora directly affects the infective capabilities of nematodes. Microplot and field experiments were conducted to determine the effects of grass rotations on the ecology of nematodes and microorganisms in soil. Results of field trials indicate that switchgrass suppressed populations of parasitic nematodes as effectively as nematicide. Work in progress on soil microflora show that switchgrass following peanut, peanut following switchgrass, and continuous peanut supported different rhizosphere microflora as reflected by the richness, or the number of genera isolated, and diversity (n1), which is a measure of richness and evenness (how many). These indices are used in classical ecological ways of looking at communities which are now being applied to microbial ecology. Number of Genera (= richness), richness more conservative, and n1=diversity index, richness and evenness=diversity. The bacterial community structure of the switchgrass rhizosphere was different from that of the peanut rhizosphere as indicated by significant differences in the genera richness, diversity, and evenness indices at 90 and 120 days after planting (DAP) (Table 5). However, none of the indices were significantly different between the peanut rhizospheres. Even though the indices did not indicate differences between the peanut rhizospheres, there were large differences among the bacterial genera that compose each community. The switchgrass rotation was strongly dominated by Bacillus spp. 60 DAP and Burkholderia spp. 120 DAP, with a relatively even distribution at 90 DAP, while the continuous peanut rotation had 2-4 genera that were dominant at any one sampling time. The bacterial community structure of geocarpospheres from continuous peanut and switchgrass-peanut rotations were significantly different at 90 DAP but not at 120 DAP. At 90 DAP more bacterial genera were present and were more evenly distributed in the geocarposphere of switchgrass rotation than in the continuous peanut; however; at 120 DAP fewer bacterial genera were present and Burkholderia spp. Were more dominant than the continuous peanuts. 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.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Kokalis-Burelle, N., R. Rodríguez-Kábana, C. F. Weaver, and D. G. Robertson. 1994. Effects of annual warm-season forage grasses on nematode populations and yield of eggplant. Phytopathology 84:1128

Kokalis-Burelle, N., R. Rodríguez-Kábana, D. G. Robertson, W. F. Mahaffee, J. W. Kloepper, and K. L. Bowen. 1995. Effects of forage grass rotations on soil microbial ecology and nematode populations. Phytopathology 85:(abstr.).

Kokalis-Burelle, N., R. Rodríguez-Kábana, J. W. Kloepper, D. G. Robertson, and W. F. Mahaffee. 1996. Effects of switchgrass rotations on soil microbial ecology, and nematode development. Phytopathology: (abstr.).

Kokalis-Burelle, N., R. Rodríguez-Kábana, J. W. Kloepper, W. F. Mahaffee, and K. L. Bowen. 1996. Effects of switchgrass rotations with peanut and cotton on nematodes and soil microflora. Third International Nematology Congress, Guadeloupe, July 1996. (Abstr.)

Rodríguez-Kábana, R., and N. Kokalis-Burelle. 1996. Cropping systems - Management of soil suppressiveness for nematode control. Third International Nematology Congress, Guadeloupe, July 1996. (Abstr.).

Kloepper, J. W., R. Rodríguez-Kábana, and N. Kokalis-Burelle. 1996. A review of antagonistic plants as modifiers of rhizosphere bacteria. Third International Nematology Congress, Guadeloupe, July 1996. (Abstr.).

Mahaffee, W. F., N. Kokalis-Burelle, J. W. Kloepper, and R. Rodríguez-Kábana. 1996. Effects of a peanut-switchgrass rotation on rhizosphere bacterial community structure. (Abstr.)

Paudel, Krishna, P. 1995. Economic Analysis of Input Application Decisions in a Peanut Cropping System. Masters Degree Thesis. Department of Agricultural Economics, Auburn University.

Paudel, Krishna P. , N. R. Martin, Jr., G. Wehtje, T.Grey. 1995. Economic Decision Making Using Enterprise Budgeting and Statistical Analysis: An Illustration of Weed Control Practices in Peanut Production. Journal of Production Agriculture: In Review.

Paudel, Krishna P. , N. R. Martin, Jr., G. Wehtje, T.Grey. 1996. Economic Decision Making Using Enterprise Budgeting and Statistical Analysis: An Illustration of Weed Control Practices in Peanut Production. Accepted for Presentation in February 1996 at the Decision Science Institute Meeting, Charleston, South Carolina.

Paudel, K. P., N. R. Martin, Jr., and N. Kokalis-Burelle. 1996. Economic evaluation of cropping patterns based on policy and environmental factors. Annual Meeting of American Agricultural Economics Association, San Antonio, TX, August, 1996.

Paudel, K. P., N. R. Martin, Jr., N. Kokalis-Burelle. 1996. Economic and environmental evaluations of peanut rotations with switchgrass and cotton. Highlights of Agricultural Research, Alabama Agricultural Experiment Station, Vol. 43, No. 1, Spring, 1996.

Paudel, Krishna P. and N. R. Martin, Jr. 1996. Risk and Input Selection in Share Tenancy: An Illustration in a Multi-Crop Situation. Accepted for Presentation in February 1996 at the Southern Agriculture Economists Association, Greensboro, North Carolina.

Education and Outreach

August 24, 1995, Wiregrass Substation, Headland Alabama, Field Day

September 5-8, 1995, Tri-State Peanut Tour, Headland Alabama

Project Outcomes

Project outcomes:

The rotation system tested in this project could be applicable to all of the peanut growing regions of the southeastern U. S., including Alabama, Georgia, Florida, North Carolina, South Carolina, and Virginia. This research could lead to reduced nematicide use and increased use of perennial forages in rotation with annual crops. The result of this would be less contamination of groundwater with nematicides, increased soil organic matter, and less soil erosion from use of the forage crop, and more economically sustainable, integrated crop and livestock production in the Southeast. It is apparent that rotation of peanut with switchgrass reduces nematode populations and causes shifts in soil microbial ecology. More research is necessary to improve peanut yields which did not differ consistently among rotation systems.

Recommendations:

Areas needing additional study

Bibliography

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Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.