Animal Waste, Winter Cover Crops, and Biological Antagonists for Sustained Management of Nematodes on Cotton
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; and 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 F/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 Results
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.
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 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. Decmber 1998.