Plant-parasitic nematodes are limiting factors in cotton and other crop-production systems in the southern United States. These parasites restrict root growth and development, resulting in a general stunting of the plant and poor yields. Poor root development prevents the plant from adequately interfacing with the soil for mineral nutrition and moisture. In addition to losses in cotton yield, the inability of the plant to utilize available nutrients and moisture may result in these nutrients and/or pesticides moving into ground or surface waters and thus becoming pollutants.
Demands for poultry and pork have fostered a rapid expansion of these animal husbandry operations in the Southeast, including North Carolina. Modern techniques for animal production result in the accumulation of large quantities of waste materials in small areas in rural communities. These waste products are of major concern as sources of surface and ground-water pollution. Poultry litter contains relatively high levels of nitrogen, phosphorus, and potassium. The use of manures/litter with high-nutrient levels in lieu of chemical fertilizers is an environmentally sound method of supplying necessary nutrients to cotton while disposing of this waste product. The ammonia in animal wastes, including poultry litter, generally acts like slow-release fertilizers and can thus inhibit nematodes while supplying the plant with nitrogen in a safe manner.
A common practice in southern row-crop agriculture in the sowing of a winter cover crop to prevent soil erosion. A winter rye crop in particular is beneficial in that it suppresses the population levels of many parasitic nematodes. The influence of other winter cover crops, such as vetch, canola, and other small grains on different plant-parasitic nematodes is poorly understood. The use of winter crops also is valuable in protecting the environment since they can scavenge nutrients left from the previous crop, prevent these nutrients from moving off site, improve soil tilth, and are an important component in conservation tillage.
Addition of animal waste products to the soil and the use of winter cover crops, that are commonly grown to prevent soil erosion, are generally beneficial because they increase the organic matter content of the soil. Increasing the level of organic material in these soils improves their nutrient- and moisture-retention properties that favors the plant. Enhanced microbial activity, a result of the application of animal waste products and/or winter cover crops, can provide for an environment where antagonists of plant-parasitic nematodes, especially certain bacteria and fungi, can aid in suppressing these pests. Many of the plant-growth-promoting rhizobacteria associated with certain cover crops, especially legumes, may induce systemic acquired resistance to nematodes and other plant pathogens. All of the aforementioned factors serve to enhance sustainability of agricultural production by providing for an improved agroecosystem. Potential reductions in costly inputs used by farmers can limit their reliance on petroleum-based products for pest control and/or chemical fertilizer.
1. Evaluate the effects of the rate of poultry manure and litter, and municipal-waste compost singly and in combination with winter-cover crops and selected nematode antagonists for control of plant-parasitic nematodes on cotton.
2. Determine the potential advantages of organic sources of nitrogen versus standard fertilizers on nitrogen use efficiency and potential environmental impacts.
3. Incorporate findings into a sustainable cotton- and associated crop-production systems through a series of farmer-managed demonstration tests, tours, cotton production meetings, and extension publications.
A combination of greenhouse, microplot, and field research plots were used to evaluate a winter rye cover crop with or without poultry litter and fungi for management of root-knot, sting, Columbia lance, stubby-root and reniform nematodes in cotton. All experiments were replicated to permit statistical analysis of the results. Twenty field research experiments, fifteen in growers fields and three on experiment stations, were utilized as field laboratories. The field plots also served an educational function in that they were featured in research tours and the 1997 North Carolina Cotton Field Day to inform farmers about this work. Greenhouse and small plot tests were conducted in order to more precisely quantify the effects of selected nematode antagonists and green manure crops on these biological systems. This information has been and will continue to be disseminated to extension personnel, farmers and the general public.
About five thousand soil samples were collected over 3.5 years to measure the impact of various treatments on communities of plant-parasitic nematodes. Nutrient levels of both soil from test sites as well as poultry litter were processed to assess the effects of these variables on the agroecosystems studied. Other measurements included cotton yield, numbers of nonparasitic potentially beneficial nematodes at several sites, activity of biocontrol agents, and assessments of the cover crops.
Field experiments clearly demonstrated the benefits of application of poultry litter for management of plant-parasitic nematodes in cotton. Poultry litter was highly efficacious in suppressing population densities of root-knot, Columbia lance, stubby-root, sting, and lesion nematodes in field soils and in other experimental systems. The inclusion of fungi and bacteria that parasitize these nematodes was only marginally effective in suppressing numbers of these plant-pathogens. A rye cover crop also was effective in suppressing root-knot and Columbia lance nematodes, especially when incorporated in late spring or left on the soil surface in a no-till system. Incorporation of a rye cover crop tended to suppress other plant-parasitic nematodes such as reniform and stubby root nematodes in greenhouse and microplot tests. Three soil amendments (poultry litter and/or a rye cover crop) also resulted in the build-up of beneficial nematodes that feed on soil bacteria and fungi. In microplots, the combinations of rye and poultry litter resulted in the highest cotton yield (up to 68% increase over control) while greatly suppressing root-gall development and enhancing the reproduction of microbivorous nematodes. The 1997 results with rye, and other small grains, however, showed that some root-knot nematode populations, including race 4 of M. incognita, can reproduce on certain small grains. An extensive study focused on the identification and quantification of various organic acids formed during the decomposition of rye. Formic, acetic, propionic, butyric and valeric acids in soil solutions were monitored. Acetic and formic acids were detected by means of ion exclusion chromatography, primarily in the first 24 hours and at concentrations less than 20 µ/L. Although low molecular weight organic acids may be involved in the control of nematodes when rye is incorporated into soil, they singularly do not appear to be the primary mode of action.
IMPACT OF THE RESULTS ON SUSTAINABLE AGRICULTURE:
Cotton growers in the southern region are highly innovative and receptive to implementing new and or developing technologies. The application of animal manures is especially attractive since it can reduce the need for expensive commercial fertilizers. Similarly, many farmers are utilizing cover crops, and this practice will be adopted with increasing frequency as they learn that a cover crop can alleviate stress on cotton due to nematode problems. The use of cover crops to improve overall nematode management is especially appropriate, since interest in conservation tillage is increasing. Cover crops not only contribute to nematode management, but may aid in preventing off-site movement of nutrients and minimize inputs of soil-applied herbicides. This project thus serves to illustrate to growers the benefits of sustainable approaches to cotton production.
POTENTIAL CONTRIBUTIONS TO PRODUCERS AND CONSUMERS:
The use of poultry litter to manage nematode pests of cotton and promote soil health provides a method of biorational pest control. This practice can also reduce the rates of application of chemical pesticides and fertilizers. Thus, the proper selection and management of winter cover crops and animal waste can enhance pest management programs, scavenge surplus nutrients that would otherwise move into ground and surface waters, improve soil health, enhance soil moisture retention in porous soils, and also prevent erosion of top soils. All of the aforementioned factors can enhance sustainability of agricultural production by providing for a better and healthier agroecosystem. Potential reductions in costly inputs used by farmers can reduce their reliance on petroleum based products for pest control and or energy intensive fertilizer products. Reduced reliance on these products also serves to protect water and air quality, thus improving the environment.
1. Evaluate the effects of the rate of chicken manure and litter, and municipal-waste compost singly and in combination with winter-cover crops and selected nematode antagonists for control of plant-parasitic nematodes on cotton.
2. Determine the potential advantages of organic sources of nitrogen versus standard fertilizers on nitrogen use efficiency and potential environmental impacts.
3. Incorporate findings into a sustainable cotton- and associated crop-production systems through a series of farmer-managed demonstration tests, tours, cotton-production meetings, and extension publications.
Literature Review: North Carolina and much of the southeastern US are well suited for the production of cotton and other field and vegetable crops. The warm, sandy soils in much of the region also result in the buildup of severely damaging nematode communities on cotton (Heald & Orr, 1984; Schmitt & Barker, 1988). Nematodes that cause the greatest cotton yield losses include: Columbia lance, Hoplolaimus columbus; root-knot, Meloidogyne incognita races 3 and 4; reniform, Rotylenchulus reniformis; sting, Belonolaimus longicaudatus; and lesion, Pratylenchus brachyurus (Koenning et al., 1990). Total yield losses to nematodes in the United States have been estimated to be $8 billion per year for the US, and about $78 to $100 billion worldwide (Sasser & Freckman, 1987). These losses would be much greater without the availability of current nematode management tactics.
Traditional tactics for nematode management include crop rotation, some resistant cultivars, and nematicides (Heald & Orr, 1984). The more effective nematicides for nematode control on cotton, however, have been removed from the market due to environmental and human health concerns (Roberts 1994). Currently, investigators are evaluating many biological antagonists as potential controls for nematodes (Abu-Laban & Salem, 1992; Hoffmann-Hergarten et al., 1997; Kerry & Evans, 1996; Stirling, 1991), the use of animal wastes and various cultural practices (Fakhtar & Alam, 1991; Akhtar & Alam, 1993; Riegel et al., 1996). The limited progress to date in biological control in agriculture is due, in part, to our restricted knowledge of the ecological requirements of these organisms for survival in field situations. To exploit this tactic, we must learn from the “biological balance” typical of natural ecosystems in order to exploit these potential nematode control agents in agroecosystems (Stirling, 1991).
Although our understanding of the “biological balance” is limited, significant progress has been made in characterizing systems that offer considerable promise (Hoffmann-Hergarten et al., 1997; Stirling, 1991). The incorporation of a number of green manure cover crops into the soil results in microbial decomposition products that are nematicidal (Bouwman et al., 1993; Johnson et al., 1992; Kloepper et al., 1992; Sayre et al., 1965). Butyric acid and other toxic compounds are formed by Clostridium butyricum when rye is incorporated in natural soils (Sayre et al., 1965). Rhizosphere bacteria associated with the roots of a number of plants such as velvet bean, castor bean, swordbean, and Abruzzi rye have been found to suppress populations of the plant-parasitic nematodes, M. incognita and Heterodera glycines, on soybean (Kloepper et al., 1992). Some of these Rhizobacteria recently have been found to induce disease systemic resistance to certain plant pathogens including nematodes (Hoffmann-Hergarten et al., 1997; Wei et al., 1996). A system of identification of bacteria by fatty-acid analysis now offers an effective means of studying these organisms (Kloepper et al., 1992).
Other research has focused on the utilization of animal and industrial waste products for control of nematodes. The addition of nitrogenous soil amendments results in the formation of ammonia which is nematicidal (Rodríguez-Kábana, 1986). More recently, studies have shown that a range of organic amendments, including chicken litter or other animal wastes provide considerable protection for plants against plant-parasitic nematodes (Kaplan & Noe, 1993; McSorley and Gallaher, 1995; Riegel et al., 1996; Fortnum, unpubl.). These materials also have been used for increasing fungi that attack nematode eggs (Abu-Laban & Salem, 1992). Several North Carolina cotton growers now add animal wastes, particularly chicken litter, as a means of supplying N and may benefit from limited nematode damage (S. R. Koenning, unpubl.).
Only recently have researchers commenced evaluations of integrated biological controls of plant-parasitic nematodes through combinations of organic amendments and biological antagonists (Fakhtar & Alam, 1991; Kerry & Evans, 1996; Roberts, 1994). Some of these treatments may provide levels of control nearly equivalent to that of commercial nematicides. Although a few organisms such as Pasteuria penetrans become established and suppress nematodes under monoculture (Dickson et al., 1992), most nematode antagonists are short-lived or fail to give effective long-term nematode control in agricultural fields (Stirling, 1991; Tedford et al., 1993). In addition, increased soil organic matter often enhances the reproduction of beneficial nematodes and other favorable soil changes, resulting in greater crop yields (Bouwman et al., 1993; Ferris, 1993; Van Bruggen, 1995; Yeates, 1994,1996). Integrated cropping systems that include the use of animal waste and green-manure cover crops with minimal tillage have great potential for exploiting beneficial soil microflora/fauna while supporting high crop yields (Barker and Koenning, 1998).
Problem Statement: Plant-parasitic nematodes frequently restrict the profitability of cotton in the USA, especially in sandy coastal plain soils of North Carolina and the southeastern states (Heald & Orr, 1984; Koenning et al., 1990). Nematodes, including Columbia lance (Hoplolaimus columbus), sting (Belonolaimus longicaudatus), reniform (Rotylenchulus reniformis), and southern root-knot (Meloidogyne incognita races 3 and 4) frequently limit cotton yields by more than 5% (Heald & Orr, 1984).
Plant-parasitic nematodes suppress cotton-root growth, resulting in nutrient deficiencies, stunting, and a delay of crop maturity (Heald & Orr, 1984). The inability of the nematode-affected crop to utilize available nutrients results in inefficient use of applied fertilizers. Restricted plant growth may lead to increased leaching and/or runoff of pesticides and soil-applied nutrients, and soil erosion. Similarly, weeds are more difficult to control in an uncompetitive cotton crop.
Management of plant-parasitic nematodes relies on limited tactics, including a few resistant varieties, nematicides, rotations, and other cultural practices (Heald & Orr, 1984). Cotton cultivars resistant to the root-knot nematode are available, but are not widely used as they usually lack desired agronomic qualities. Some nematicides effectively control these pests, but the most economic ones have been removed from markets. Others currently are under review because of high toxicity, and potential to contaminate water supplies. Acceptable cotton cultivars with resistance and/or tolerance to sting and Columbia lance nematodes are not available, but some varieties have limited tolerance to the lance nematode. Rotation usually is not a viable option for sting, Columbia lance, lesion, or stubby-root nematodes since most field crops are hosts for these parasites. Thus, new tactics for managing these pathogens must be integrated into production systems to improve the sustainability of southern cotton production.
Except for rotation, cultural practices often are neglected as an option for nematode management. Use of animal wastes, other organic amendments and green manure crops have promise for controlling many nematodes (Bouwman et al., 1993; D’Addabbo, 1995). Limited studies indicate that combinations of various plant or animal materials with nematode antagonists, such as fungi and bacteria, or combinations of antagonists have promise for nematode control (Abu-Laban & Salem, 1992; Kerry & Evans, 1996; Stirling, 1991). Our increasing understanding of nematode suppression by microbes and soil amendments and improved related methodologies ( Kerry & Evans, 1996; Stirling, 1991; Tedford et al., 1995) are enhancing their potential as safe, economic management options. Still, negative aspects of using wastes on crops must be considered (Amberger, 1988; National Research Council, 1991; Van Bruggen, 1995).
North Carolina is a leading state in poultry production. This industry generates enormous quantities of wastes which require environmentally acceptable means of disposal. These materials (manure/litter) generally are applied to the land. An estimated 1.4 million tons of poultry waste, with 41, 49 and 28 thousand tons of nitrogen, phosphate and potash respectively, are produced in North Carolina annually. By increasing the efficiency of alternative nutrient sources, the nutritional needs of the crop can be met with fewer off-farm inputs, resulting in enhanced profitability. Since mineralization is required before plant available N is released, the use of these waste products can provide a source of slow-release N in soils, which may potentially reduce ground-water contamination in soils most subject to leaching (Bouwman et al., 1993; Castellanos & Pratt, 1981). Chicken litter and manure also have nematicidal or nematastatic properties (Riegel et al., 1996).
The application of manures to various crops to manage nematodes and reduce costly inputs of chemical fertilizers makes this practice more attractive to farmers. The rate of NH4+ release may directly impact the effectiveness of these materials for control of nematodes (Kaplan et al., 1992). Mineralization rates of N are expected to be rapid because of prevalent high temperature and moisture, but data on direct mineralization from animal wastes in the field in the Southeast are limited. Nitrogen mineralization rates vary greatly, depending on the source and properties of organic N (e.g., the carbon:nitrogen ratio and the degree of composting waste (Amberger, 1988; Bouwman et al., 1993).
This completed project provides for a biorational approach to nematode management as well as offering means of addressing economic means of waste utilization, reducing soil erosion, enhancing agricultural sustainability, and improving environmental quality (National Research Council, 1991). Better nematode management should reduce the need for pesticides and fertilizers, thus enhancing water quality. Potential social and economic impacts include employment opportunities in small communities for persons applying and monitoring waste and improved crop profitability.
The research described herein was conducted in greenhouses, microplots, collaborator-growers’ fields and Experiment Station fields, with replicated experiments over 3.5 years from 1994-1998. Field experiments focused on the effects of rye and either chicken or turkey litter on plant-parasitic nematodes.
FIELD EXPERIMENTS: Eighteen field experiments located in Scotland, Hoke, Robeson, Onslow, Johnston, and Wayne Counties have been conducted to evaluate levels of poultry litter and/or cover crops on nematode populations as well as cotton yield. All field experiments were sampled for nematodes prior to addition of chicken or turkey litter, before cotton planting in April or May, August or September (midseason), and after cotton harvest (October or November). All plots were 20 ft long with 7-ft alleys and four rows. The alleys were left in place throughout the growing season and were cut only near harvest to eliminate boundary effects on yields. Row spacing varied from 30 to 40 inches, depending on which spacing the farmer was using. All plots were arranged in randomized complete blocks or in split-plot designs with five-to-eight replications. Standard management practices for North Carolina cotton production were followed in all experiments. In each case, the farmer planted the crop, using standard practices and the cotton variety that they had selected for that particular field. Baseline nutrient status of all sites were determined by soil tests. Plots receiving no litter or low levels of litter received supplemental fertilizer at recommended rates based on soil tests.
IMPACT OF POULTRY LITTER ON NEMATODE COMMUNITIES: Two initial experiments were conducted in 1995 in Hoke and Scotland Counties, NC. These experiments were conducted to determine if the growth regulator PIX could be used to prevent excessive growth of cotton fertilized with different levels of chicken litter. Turkey litter was applied to plots at the rate of 0, 3, 6 or 9 tons/acre in April, 1995. Litter was incorporated within 1 wk of application. The site located in Scotland County, NC, had damaging levels of Columbia lance nematode, whereas the population densities of plant-parasitic nematodes were below thresholds at the Hoke County site. In this particular experiment, all plant-parasitic nematodes were identified to genus and, furthermore, all nematodes were identified to trophic levels (as to whether they were predators, fungivores, bacterivores, or omnivores) and this data were also analyzed to determine if litter applications affected the trophic structure of the nematode community in these particular soils.
OPTIMIZATION OF RATE AND TIMING OF LITTER APPLICATION FOR NEMATODE MANAGEMENT: Two series of replicated experiments were used to determine the effects of date of litter application on population densities of Columbia lance nematode and cotton yields. The litter was applied to selected plots in December, March or April at 0, 3, 6, and 9 tons/acre. Litter was incorporated after application in each case. Plots were arranged in a factorial design at two locations, one in Scotland and one in Hoke County, NC. A second series of experiments were initiated in 1995-96 and repeated in 1996-97 in Scotland County. This series was a split-plot design with application dates as whole plots at 0, 4, 8 and 12 tons per acre (4 rates subplots). Litter was incorporated within 5 days of application.
FALL APPLICATION OF POULTRY LITTER WITH OR WITHOUT A COVER CROP: Two field sites were used in the fall of 1994 located in Scotland and Robeson Counties. It consisted of fall applications of chicken litter obtained from Scotland County at rates of 0, 1.5, 3, and 4.5 tons/acre, applied in late November, 1994. Selected plots in this experiment also received a rye cover crop. All rye was disced in May, and cotton was planted in mid-May. Yields were determined in mid-November, 1995.
TILLAGE AND COVER CROP INFLUENCE ON COLUMBIA LANCE NEMATODE: This experiment was conducted to evaluate effects of a rye cover crop grown under minimum-till or conventional tillage systems and was located in Hoke County near Lumber Ridge, NC. Rye was planted over the entire area in December of both 1994 and 1995. Rye was killed in selected plots at this time so that there would be no rye treatment versus incorporation of the rye in early March, mid-April, or allowing the rye cover crop to continue growing. This research was conducted in two areas of the same field each year. Plots were planted with minimum tillage, although all plots were subsoiled under the row at planting. This field was infested with Columbia lance nematode (H. columbus).
COVER CROP SELECTION AND MANAGEMENT FOR NEMATODE SUPPRESSION IN COTTON: A series of field experiments were initiated in 1996 to evaluate different cover crops, their management, and application of litter or fertilizer on population densities of parasitic nematodes and cotton yield. Sites infested with Columbia lance nematode were located in Scotland and Hoke Counties, NC.
A factorial experiment to examine the influence of rye, canola, oats, vetch, wheat, and fallow was established in Hoke County in 1996. Unfortunately, due to winter kill and saturated soil, only rye grew. Three remaining treatments consisted of rye, fallow, and rye plus 20 lbs/acre N-P-K.
An experiment in Scotland County was conducted to evaluate time of incorporation of rye with or without poultry litter on Columbia lance nematode. Treatments were arranged in a RCBD with eight replications. Specific treatments included killing rye in March with Glyphosphate, discing in March, application of 20 lbs N-P-K/acre in March and discing in April, and addition of 0, 3 or 6 tons of poultry litter to the rye in April followed by discing. Plots were planted in late May of 1997 and harvested in November.
A split-plot experiment was also established in November, 1996, with four cover crops as sub-sub plots (fallow, wheat, rye, Canola), litter treatments as sub plots (0 vs. 4 tons/acre) and a management trial (strip kill vs. all kill with Glyphosphate) as whole plots. Roundup ready cultivar 1560RR was then planted no till in May of 1997 and harvested in November. This experiment was repeated in 1998.
POULTRY LITTER RATES FOR MANAGEMENT OF ROOT-KNOT NEMATODES IN COTTON: Two research/demonstration experiments were conducted to determine the optimal rates of litter application for management of root-knot nematode on cotton in 1997 and repeated in 1998. The first experiment was arranged as a RCBD with seven rates of poultry litter (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 tons/acre chicken litter) and a susceptible variety. This experiment was located in Onslow Co. in 1997 and in Wayne Co. in 1998. The second experiment featured a split-plot design with resistant LA 887 and susceptible Deltapine 20 as sub plots and litter rate (0, 1.5, 3.0, 4.5, 6.0, and 7.5 tons/acre), turkey litter as whole plots with five replications.
The experimental locations were the Upper Coastal Plain Experiment Station near Rocky Mount, NC, in 1997 and the Central Crops Research Station near Clayton, NC, in 1998. This experiment was featured at the North Carolina Cotton Field Day in 1997. Midseason and harvest population densities of nematodes were determined as well as cotton yield for both experiments.
GREENHOUSE EXPERIMENTS ON BIOLOGICAL CONTROL AND SOIL AMENDMENTS:
One bacterium and three fungi were evaluated as biocontrols of root-knot nematodes and the often associated fungus Rhizoctonia solani. The bacterium, Burkholderia cepacia (BC-5.5B), was grown 3 days in nutrient broth, then centrifuged twice in water to remove nutrients. Bacteria were coated onto Deltapine-50 cotton seeds (7,500 cfu/seed) in 1% methyl cellulose and allowed to air-dry before planting. Binucleate Rhizoctonia fungi (BNR), isolates BNR621 and P9023 along with Paecilomyces lilacinus (PI-6.2f) were formulated as 20% wheat bran biomass after 7 days colonization into a pesta formulation (semolina wheat flour and kaolin clay, 4:1, w/w). This dough was rolled into thin sheets, air-dried overnight in a laminar flow hood, then pulverized to granules in a blender and sieved through 20-mm openings. These granules were incorporated at a rate of 0.2% (4 g/pot, about 1200 cfu/g) in 2 kg sandy loam mix that was added to 15-cm-diam. clay pots. Inoculum of isolate RS3 of Rhizoctonia solani (Rhizoc) was prepared by blending colonized oat-grain cultures in water and sieving through 2-mm openings. Inoculum density was 51 cfu/cm3 (4-wk old) and 50 cfu/cm3 (2-wk old) in experiment I and II, respectively. Eggs of race 3 of M. incognita (RK) were extracted with NaOCl from tomato roots. RK eggs were used at 6.7 eggs/cm3 and 13.3 eggs/cm3 soil in experiments I (June 26) and II (July 16), respectively. Soil mix for each pot (1500 cm3) was infested with RK eggs and Rhizoctonia inoculum and amended with the pesta granules of the putative biocontrol agents in plastic bags. A captan-treated seed control, along with infested controls with both pathogens in combination or singly, and uninfested controls were included. A RCB design with nine treatment applications and five cotton seeds per pot were used. Hypocotyl rot was rated on a 1.5 scale with 1=healthy, 2=slight necrosis, 3=moderate necrosis, 4=severe necrosis, entire stem girdled, 5=dead plant. Root-gall index was on visual scale of 0-100%.
Another series of greenhouse tests focused on the relative suitability of selected small grains as hosts for root-knot nematode species and host races and the efficiency of these plants as green manure “cover” crops. The test plants included ‘Starling’ barley, ‘Boone’ barley, ‘P2684′ wheat, ‘NKC 9543′ wheat, ‘55-76-30′ oats, ‘Brooks’ oats, and ‘Abruzzi” rye. Nematodes used were: M. incognita races 1, 2, 3 and 4; M. arenaria races 1 and 2, and M. javanica. Clay pots (15-cm-diam.) filled with a 1:1 mixture of sand/sandy loam soil were seeded with given small grain cultivars and inoculated with 10,000 eggs of a given nematode population. Some 12 weeks after inoculation, shoots of plants were clipped and weighed, and the roots removed. Nematode-induced root galling and necrosis were assessed on a 0 to 100 scale (0=no galls; 100%=entire root galled or necrotic). Nematode eggs were extracted from 5-gm root samples by the NaOCl procedure. Nematode juveniles were extracted by elutriation-centrifugation.
In comparison experiment (each test repeated with 5-8 replicates/treatment), the shoots of the small-grain plants were chopped into about 2.5-cm sections and incorporated into the same type soil-sand mix, using 15-cm pots. Rates of material added were 0, 25, 50 and 100 gm per pot. Pre-germinated cotton seedlings (3 days old) were transplanted and inoculated with 20,000 eggs of M. incognita. The tests were also terminated 12 weeks after inoculation. The cotton roots were removed and assessed for nematode development (numbers of juveniles) as well as root-gall development.
MICROPLOT EXPERIMENTS: Two microplot experiments were conducted with Cotton variety, Deltapine 20, at the Central Crops Research Station near Clayton, NC. Microplots were fumigated with methyl bromide-chloropicrin in October, 1994. Abruzzi rye was planted at the rate of 2 bushels/acre in selected microplots in early November 1994 and subsequent years. The sting nematode, Belonolaimus longicaudatus, was reared in the greenhouse on soybean, and the root-knot nematode, Meloidogyne incognita race 4, was reared on tomato. The experiments were 2x3x2 factorials with two levels of the nematode attacking fungus, Paecilomyces lilacinus (+ or -), three levels of chicken litter (¼, ½, and ¾ tons/acre) and two levels of rye (+,-). Plots were arranged in two randomized complete blocks with six replications. One experiment contained the root-knot nematode, Meloidogyne incognita race 4, while the second experiment contained the sting nematode, Belonolaimus longicaudatus. Only data from the first experiment with root-knot nematode are given in this report.
Rye was cut in mid-May 1995 and subsequent years and incorporated into the plots. The beneficial mycorrhizal fungus, Glomus macrocarpus, was added initially to all plots as was inoculum of root-knot nematode. Selected plots received the nematode-attacking fungus, Paecilomyces margarita. Turkey litter was incorporated into selected plots at three rates. Deltapine 20 cotton was planted on 23 May 1995 in all plots. Standard management practices for cotton production in North Carolina was followed thereafter. Cotton was harvested on 14 November 1995. Midseason nematode samples were taken in September and processed by elutriation and centrifugation to extract juveniles from the soil and roots were processed with clorox to extract eggs. Final nematode assays were based on soil samples collected at harvest. Cotton-root systems were rated for galling by root-knot nematodes on 27 November 1995. These experiments were repeated in 1996, 1997, and 1998 with carry-over nematodes serving as the inoculum.
ASSESSMENT OF ORGANIC ACIDS PRODUCED VIA DECOMPOSITION OF RYE IN SOIL: For this test, a sandy loam soil (Goldsboro series, a fine-silty, siliceous, thermic aquic paleudilt) was taken from a field near Clayton, North Carolina. The rye used (Abruzzi) was grown in 15-cm-diam. clay pots in a greenhouse. The rye was fertilized weekly with N, P, and K in the irrigation water and periodically with controlled-release N, P, and K fertilizer. Plants used were approximately 10 weeks old, and the shoots were cut into 2.5-cm segments before being incorporated into the soil.
The fresh field soil was added to 15-cm clay pots at a rate of 1450 grams of soil (oven-dry weight) per pot. Three application rates of fresh rye were established by ad ding zero, 80 grams rye fresh weight (23 grams dry weight), and 120 grams rye fresh weight (34 grams dry weight) per pot. Three repetitions were randomized in three blocks in a temperature-controlled incubator where they were maintained between 28° and 29° C. Soil moisture content was brought up to 80% of saturation each day with distilled water.
For organic-acid sampling, the three treatments were sampled from each block for organic acids at 0, 12, 36, 84, and 180 hours. A leachate sample was obtained by slowly adding distilled water to the surface of the soil in the pot. When water was observed dripping from the bottom of the pot, an additional 200 ml were added and allowed to drain into a glass jar. The pH of each sample was measured and subsequently adjusted to pH 5 with sodium hydroxide or hydrochloric acid and stored at 1° C in glass containers with Teflon-lined lids. The pots were immediately returned to the incubator to maintain the environmental conditions.
Prior to analysis of the leachates for organic acids, the samples were allowed to warm to room temperature and helium was bubbled through each sample for approximately 20 minutes, to eliminate carbonate in solution. When left untreated, the carbonate in the samples resulted in a negative peak during analysis which obscured the propionic and butyric acid peaks. The samples were analyzed for formic, acetic, propionic, butyric, and valeric acids by means of ion exclusion chromatography. Individual organic acid separation was determined by ion chromatography exclusion (ICE) using a Dionex model DX100 ion chromatograph equipped with a Dionex Ionpac ICE-AS1 column, Dionex AMMS-ICE suppresser, and conductivity detector. The eluent was 1.0 mM heptaflorobutyric acid in HPLC-grade water at a flow rate of 2 ml/minute at a column pressure of approximately 4800 kPa (700 psi). The regenerate was made by adding 50 ml 55% aqueous TBAH (tetrabutylammonium hydroxide) per liter of HPLC-grade water. Regenerate flow rate was approximately 1 ml/minute. Quantification of the acids was determined by peak area. The sample concentrations were, in turn, converted to the concentration of organic acids in soil solution (at 80% of saturation) by taking into account the dilution occurring during the leaching process and the amount of solution recovered from the pots.
IMPACT OF POULTRY LITTER ON NEMATODE COMMUNITIES: There was a linear decrease (P=0.05) in numbers of Columbia lance nematode at midseason with increasing amounts of litter added at the Scotland County site. Population densities of the plant-feeding nematodes, Helicotylenchus dihystera, Tylenchorhynchus claytoni and Paratrichodorus minor, were unaffected at midseason or at cotton harvest by litter applications (Appendix A, Table 1). Similar results were obtained at a site in Hoke County, NC, although plant-parasitic nematodes were below the damage threshold at this location.
Midseason numbers of bactivores were positively related (P=0.05) to the rate of litter application at both sites, whereas numbers of fungivorous nematodes at cotton harvest were proportional to the amount of manure applied. There were greater (P=0.10) numbers of predatory nematodes at midseason in plots with high rates of litter than the controls at the Hoke County site (data not included). The soil application of poultry litter effected a shift in the relative abundance of nematodes in various trophic groups. The percentage of fungivorous and bactivorous nematodes increased relative to the percentage of phytophagous nematodes at both sampling dates at both locations.
The 6 and 9 ton/acre rates of chicken litter effected an increase (P=0.10) in cotton lint yield associated with midseason suppression of CLN at the Scotland County location. Similarly, there was a linear increase in cotton-lint yield related to the rate of litter applied at the Hoke County site, even though preplant population densities of H. columbus were below the damage threshold.
OPTIMIZATION OF RATE AND TIMING OF POULTRY LITTER APPLICATION FOR NEMATODE MANAGEMENT: The first set of experiments on dates and rates of poultry litter application on Columbia lance nematode showed a distinct reduction in numbers of this nematode at midseason (Appendix A, Table 2). Nematode population densities at other sampling dates were unaffected. The suppression of midseason numbers of CLN effected a linear increase in cotton-lint yield (P=0.10). There was a trend toward improved nematode control with early (December) application dates, but this factor was borderline for significance.
In order to gain more information on the impact of poultry litter rates on Columbia lance nematode, and clear up ambiguity about the influence of date of application on control and cotton yield enhancement; a second set of experiments was initiated for 1995-1997 utilizing a split-plot design. The rate of poultry litter application was negatively related to numbers of CLN at midseason (Appendix A, Table 3).
Similarly, cotton-lint yield was enhanced by poultry litter application. Results from the two sets of experiments indicate that 4-6 tons of poultry litter are optimal for cotton-yield enhancement. Although high rates of litter application were more effective in suppressing CLN, cotton-lint increases with high rates were marginal (Appendix A, Table 3). Also, 4-6 tons of poultry litter are adequate to supply the nutritional needs of the crop. This last series of experiments also demonstrated that the date of application had little impact on control of CLN or cotton-lint yield.
FALL APPLICATION OF POULTRY LITTER AND RYE COVER CROP: Applications of rates of poultry litter from 0—4.5 tons/acre in the fall established that more than 3 tons/acre must be applied to suppress CLN and enhance cotton-lint yield (Appendix A, Table 4). Only the 4.5 ton/acre rate was effective in achieving midseason suppression of Columbia lance nematode. Althougth a rye cover crop also suppressed CLN; allelopathic effects of the rye on the cotton crop negated the benefits of this practice (Appendix A, Table 4). There was no effect on stand establishment at another site, but cotton-lint yield was still negatively related to the amount of rye biomass.
TILLAGE AND COVER CROP INFLUENCE ON COLUMBIA LANCE NEMATODE MANAGEMENT: The impact of a rye cover crop and tillage practices on Columbia lance nematode and cotton was studied in a farmer’s field in Hoke County, NC, from 1994-1997. Midseason population densities of Columbia lance nematode tended to be lower in plots with a rye cover crop compared to plots without rye (Appendix A, Table 5). Early incorporation of the cover crop resulted in highest population densities of this nematode among plots with rye, suggesting that suppression of plant-parasitic nematodes by a rye crop is related to the amount of biomass incorporated. The tillage system did not affect levels of the Columbia lance nematode, but did impact densities of another plant-parasitic nematode, Scutellonema brachyurum, in 1995. The highest cotton-lint yields occurred in plots in which the rye was tilled under in mid-April, about 3 weeks prior to cotton planting on rye that was killed before planting (Appendix A, Table 5). These data indicate that various factors such as the amount of rye present, weed composition, and avoidance of allelopathic effects must be better understood.
COVER CROP SELECTION AND MANAGEMENT FOR NEMATODE SUPPRESSION IN COTTON: An experiment was established in Hoke Count in fall, 1996, to measure the impact of fallow, rye, Canola, vetch, oats and wheat on Columbia lance nematode with or without fertilization. Only rye became established in this experiment. Although rye tended to enhance cotton-lint yield, no impact on CLN was detected at midseason (Appendix A, Table 6). Drought in August necessitated sampling in September which may have precluded the detection of significant differences.
Two experiments were conducted on cover crop incorporation date with and without litter from 1995-1997 in Scotland County (96 SARE/ACE report). Surprisingly, incorporation of rye with poultry litter resulted in highest numbers of CLN and lowest cotton yield (Appendix A, Table 7). Incorporation of the two materials simultaneously may result in ammonia and butyric acid being unavailable for nematode control at the proper time. Although this result was not anticipated, it partially confirmed results from 1995-1996 (Barker, SARE/ACE Report 1996).
In an additional experimental site in Scotland County, a split-split plot design was utilized to evaluate wheat, rye, Canola and fallow with or without poultry litter and strip vs. all kill of cover crops in the spring. Poultry litter was efficacious in suppressing midseason numbers of Columbia lance nematode (P=0.05) (Appendix A, Table 8). Cotton-lint yield however, was unaffected since pretreatment population densities of Columbia lance and root-knot nematodes were below thresholds. Cover crops tended to suppress numbers of root-knot nematodes compared to fallow, probably, in part, a function of nematode reproduction on winter weeds. Canola grew poorly or not at all unless litter was applied. The treatment with Canola and litter resulted in highest (P=0.10) numbers of CLN (Appendix A, Table 8). Canola should probably not be used as a cover crop when this nematode is present.
POULTRY LITTER RATES FOR MANAGEMENT OF ROOT-KNOT NEMATODES IN COTTON: Application of 0—9 tons/acre of poultry litter enhanced cotton-lint yield in field plots in Onslow County, NC, infested with root-knot nematodes (Appendix A, Table 9). Optimal rates for suppression of this nematode and cotton-lint yield were between 4 and 6 tons/acre (Appendix A, Table 9).
A second experiment at the Upper Coastal Plain Experiment Station near Rocky Mount, NC, illustrated the benefits of resistance to root-knot nematode on the use of litter to manage this nematode in cotton production. Yield of susceptible Deltapine 20 cotton increased linearly with respect to the rate of litter applied, whereas resistant LA 887 cotton was largely unaffected by the addition of litter (Appendix A, Table 10). The application of more than 6 tons/acre of litter appeared to suppress yields of both cultivars.
GREENHOUSE EXPERIMENTS ON BIOLOGICAL CONTROL AND SOIL AMEND-MENTS: Three greenhouse and one microplot tests were carried out to evaluate the potential of four cotton-pathogen antagonists as biological controls for root knot caused by M. incognita and damping-off induced by the fungus, R. solani. Potential interactions by these two pathogens also were assessed (Appendix A, Table 12). In regards to emergence of the cotton seedlings, none of the antagonists affected the activity of R. solani as has been described on woody ornamentals (D. M. Benson, persl. communication). In fact, the two binucleate Rhizoctonia spp. caused the development of superficial necrosis on the roots and hypocotyls of the cotton seedlings. Burkholderia cepacia failed to control R. solani or M. incognita, even though it has been reported to be effective against both pathogens on other plants (D. M. Benson, persl. communication).
Only Paecilomyces lilacinus provided significant suppression of root-gall development caused by M. incognita (Appendix A, Table 12). The greatest inhibition of gall development by this fungus was 33%. The data from the microplot test are not presented as all potential biocontrol agents failed to suppress the pathogens evaluated. Based on the low efficacy in the biocontrol tests in 1995 and 1996, available biocontrol agents against plant-parasitic nematodes on cotton must be integrated with other management tactics.
Additional greenhouse experiments focused on the relative host suitability of selected small grain cultivars, including those often used as green-manure cover crops in North Carolina to root-knot nematodes. The primary experiment, repeated twice included seven Meloidogyne populations and seven, small grain cultivars (Appendix A, Table 13). Although root-galling across all cultivars differed only slightly, M. javanica, M. incognita race 4, M. incognita race 1, and M. arenaria race 2 reproduced at the greatest rates (Appendix A, Table 13). With only one exception (M. incognita race 1), these nematodes attacked the M. incognita-resistant tobacco with which they are associated in the state (rye is used as a green-manure cover crop with tobacco as well as cotton). The two cultivars of barley and ‘P2684′ wheat proved to be fairly good hosts for the Meloidogyne populations, as reflected by root-gall indices and numbers of eggs and juveniles (Appendix A, Table 14). All nematode populations induced more root-gall development on barley than on the other crops. With the exception of M. incognita race 4 on ‘55-7630′, oats supported little nematode reproduction (Appendix A, Table 15). Abruzzi rye also supported considerable reproduction of M. incognita races 1, 2, and 4 as well.
In the comparison test to determine the effects of incorporating fresh shoots of small grains in soil to suppress root knot, barley and wheat were almost as effective as rye (Appendix A, Table 16). Overall, the oat amendment was the least effective in controlling root-knot development on cotton. The intermediate and high rates of amendments were less effective in Test II than in Test I; this apparently was due to the plants Based on nematode development on barley and wheat (Appendix A, Tables 14, 15), however, rye is still the best small grain for use as a green-manure cover crop in a cotton-nematode management system.
ASSESSMENT OF ORGANIC ACIDS PRODUCED VIA DECOMPOSITION OF RYE IN SOIL: Only small concentrations (less than 450 µg/ml) of formic acid and acetic acids were detected in the treatments of 80 and 100 grams of rye, and they were primarily present during the first 24 hours after rye application, although formic acid was measurable again at 180 hours (Figure 1).
Formic acid and acetic acid accounted for 75% of the total aliphatic acids present in the soil during the 8-week study. The barely detectable levels of butyric acid in our work were much lower than those reported in earlier work (Sayre et al., 1965).
MICROPLOT EXPERIMENTS: The influence of a rye cover crop, Paecilomyces marquandii and poultry litter at three rates on cotton yield in the presence of the root-knot or sting nematode was evaluated in two microplot experiments. Cotton yield was unaffected because low initial nematode numbers were used in order to better evaluate the treatment effects on the nematode population density. The gall rating of cotton infected with root-knot nematode was suppressed by the rye cover crop (Appendix A, Table 17). The significant second order interaction indicates that high rates of litter application tended to suppress the activity of the fungus in the presence of rye. A possible explanation is that the system may have been overloaded with amendments. Cotton yield was significantly increased (P = 0.06) by a rye cover crop when the sting nematode was present (Appendix A, Table 17). This nematode is a highly destructive pest when present even in low numbers, and any reduction in its pathogenic potential is important. The chicken litter X rye interaction was significant (P = 0.03). In 1998, the combinations of rye and poultry litter resulted in the highest cotton yield (up to 68% over control) while greatly suppressing host-gall development and enhancing reproduction of bacteria and fungal-feeding nematodes (Table 18).
MAJOR PROBLEMS ENCOUNTERED: The main difficulties encountered in carrying out this project have concerned timing. It has been difficult harvesting plots then getting cover crops in before it is too cold. Most cooperators have been willing to work with us. They have not, however, been interested in attending meetings on sustainable agriculture. Southern SARE has been helpful in most instances. A later reporting date – January would allow for more meaningful results. Typically, cotton is harvested in November; so, we are pressed to analyze data before we can initiate field work (winter cover crops in November) for next year. The philosophical framework, provided by SARE has been the most helpful aspect of Southern SARE. Their flexibility in allowing extensions is also a great help.
Educational & Outreach Activities
BARKER, K. R., and S. R. KOENNING. 1997. Interactions of Meloidogyne incognita populations with selected cotton cultivars. J. Nematol. 29:569 (Abstr.). BARKER, K. R., and S. R. KOENNING. 1998. Developing sustainable systems for nematode management. Annu. Rev. Phytopathol. 36:165-205. BARKER, K. R., S. R. KOENNING, and K. M. PARKER. 1998. Relative host suitability of small grains for Meloidogyne species and potential problems with their use as green-manure crops. J. Nematol. 30:(in press) Abstr. BARKER, K. R., S. R. KOENNING, and D. T. BOWMAN. 1996. Management of Columbia lance nematode with animal manure and winter cover crops. Cotton Incorporated Agricultural Research Projects Summary Reports, 1995, p. 77. BARKER, K. R., S. R. KOENNING, R. L. MIKKELSEN, K. L. EDMISTEN, D. T. BOWMAN, and D. E. MORRISON. 1996. Management of plant-parasitic nematodes in cotton production with poultry litter and winter rye. Proceedings of The Third National IPM Symposium/Workshop. p. A-54. KOENNING, S. R., K. R. BARKER, and K. L. EDMISTEN. 1996. Changes in nematode community structure and cotton productivity as affected by poultry-litter amendments. Proceedings of The Third National Nematology Congress, p. 170. KOENNING, S. R., and K. R. BARKER. 1997. Changes in population densities of plant-parasitic nematodes in cotton fields amended with poultry litter. J. Nematol. 29:590. McBRIDE, R. G. 1998. The contribution of low molecular weight organic acids from decomposing rye to suppression of root-knot nematode populations on cotton. M.S. Thesis, North Carolina State University, Raleigh.
Discussion of this work and related interaction/collaboration with growers and county extension personnel were initiated in 1994. Information and available data on the potential use of poultry litter and cover crops for managing Columbia lance nematode were disseminated at the Cotton Quality Improvement Meeting in March of 1994 and 1997 when additional support for related research from Cotton Incorporated was solicited. Approximately 30 individuals associated with cotton production were in attendance. These were largely cotton growers, but also included cotton ginners and other members of the cotton-production community such as cotton breeders, and other industry members. Preliminary information was presented at the Scotland County Cotton Tour in the summer of 1994 and at the Tri-County Cotton winter meeting held jointly for Hoke, Robeson, and Scotland Counties at Midway, NC, in February of 1995, 1996, 1997, and 1998, approximately 75 growers attended each meeting. The Scotland County Commissioners viewed one of these research plots as an example of the benefits of the Cooperative Extension Service in the spring of 1995. The management of nematodes through the use of poultry litter and a rye cover crop was the main feature of the combined Scotland-Robeson County tour in September of 1995 and the Scotland County Cotton Tour in 1997. This information was also included in training for county extension agents at the North Carolina Annual Fall Cooperative Extension In-Service Training for agricultural agents involved in cotton production with 56 agents registered in 1995. One experiment was featured on the North Carolina Cotton Field Day held in September 1997. As a result of the field day, this information was featured in the Southeast Farm Press (24:20 3,12). More of this information was utilized in February, 1997, for the Greene County Nematode Management Series. Nematode management, including the use of poultry litter, was presented at the Southeast Cotton Conference in January, 1998, and at the North Carolina Crop Protection School in December, 1998.
The use of cover crops and poultry litter to manage nematode pests of cotton and promote soil health provides a method of biorational pest control that can also reduce the rates of application of chemical pesticides and fertilizers while converting a waste product into a useful material. The proper selection and management of winter cover crops can enhance pest management programs, scavenge surplus nutrients that would otherwise move into ground and surface waters, improve soil health, soil tilth, improve soil-moisture retention in porous soils, and also serve their primary purpose of preventing erosion of top soils. All of the aforementioned factors serve to enhance sustainability of agricultural production by providing for a better and healthier agroecosystem.
North Carolina has approximately 900 cotton growers who utilize between 650 – 800 thousand acres of land for cotton production. The estimated 1.4 million tons of poultry litter produced in this state is enough to supply more than enough nutrients for the entire NC cotton crop. As a result of this project, some 300 growers and numerous consultants and extension service personnel have been made aware of the potential for managing plant-parasitic nematodes in cotton and other crops with poultry litter. This provides an additional incentive for growers to utilize these materials on high-value crops such as vegetables or cotton that can utilize the nitrogen rather than soybean where this nutrient is not necessary.
Similarly, the increased use of cover crops by cotton growers will reduce the amount of nutrient-laden sediment that pollutes surface waters (48% of pollution). Now that growers are aware of the benefits of winter cover crops for nematode management, this is yet another incentive to employ cover crops. In addition, cover crops scavenge residual nutrients and prevent their movement into ground and surface waters.
Areas needing additional study
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