The practice of agriculture produces, as a by-product, large amounts of waste materials of vegetable origin. Heretofore, such waste materials were disposed of by burning or by removal to a dump. The lack of available dump sites and increasingly more stringent federal and local regulations regarding burning, transporting and dumping of waste materials has made disposal of such materials more difficult.
It is known that waste materials of vegetable origin can be converted by composting to a humus-like substance, or organic soil, useful in supporting plant growth, while at the same time suppressing or eliminating soil-borne plant pathogenic microorganisms, viruses, insects, weed seeds and certain organic insecticidal and herbicidal residues and related materials harmful to animals and to plant growth. The beneficial effort of mixing of soil with humus obtained by composting vegetable waste, or the application of such humus to soil, was attributed to the presence of organic fibers, nutrients and various trace minerals in the humus.
Cotton gin waste is an example of troublesome, yet potentially valuable vegetable waste material. As taught in U.S. Pat. Nos. 4,164,405 and 4,229,442, cotton gin waste is produced in great quantities, about 150 pounds of waste per each 500-pound bale of cotton lint. In previous years, cotton gin waste was burned in open refuse burners producing a smoke which contained various toxic substances, including those derived from pesticidal chemicals used to treat growing cotton. Primarily for that reason, the open burning of cotton gin waste is now prohibited. Also, because cotton gin waste may contain plant pests, it cannot legally be moved off the premises where the gin is located unless certified free of pests by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service.
Cotton gin waste is an excellent organic fertilizer, except that like other agricultural waste materials it may contain plant disease-causing agents, insects, weed seeds and pesticidal residues detrimental to plant growth. Likewise, it also contains microorganisms, the most commonly present being mesophylic forms of bacterial, fungi and actinomycetes commonly found in soil at temperatures up to about 105.degree. F.
Various composting processes are known for converting cotton gin waste into a useful humus-like material. As the temperature increases during composting, most of the insects, weed seeds and pesticidal residues are killed or destroyed. Also, essentially all of the mesophylic plant pathogens are killed. Then, the thermophyllic fungi, bacteria and actinomycetes flourish bringing the temperature of the compost pile up to about 140.degree. to 150.degree. F.
During and after composting, various microbial biodegradation products are released in the compost as metabolic by-products of the multiplicity of microbial species present in the compost pile. Certain of these microbial biodegradation compounds are antagonistic to Rhizoctonia solani and other plant disease-causing agents, and can be designated as antibiotics. Contrary to the situation in untreated soils, these antibiotics are continuously regenerated for several months as the microorganisms present continue to ferment the carbon and nitrogen containing sources still available.
U.S. Pat. Nos. 3,420,936 and 3,346,447 teach the use of hexachlorophene, 2,2'-methylene-bis-(3,4,6-trichlorophenol), and its salts, as an antimicrobial to control fungal and bacterial diseases attacking the foliage of plants and to control plant fungal diseases in the soil. Previous workers assumed that the beneficial results obtained by the treatment of soil or the like with chemical antimicrobials was due to control of one or more of the fungal pathogens present. However, in 1982, Schroth and Hancock reported, in Science, Vol. 216, June, 1982, that microorganisms in and around the roots of a plant could influence the growth of the plant in a positive manner. They reported that root microflora can be altered qualitatively and quantitatively by inoculation of seeds, seed pieces or roots with beneficial bacteria and fungi, such as certain species of Rhizobacteria, and this can lead to substantial increases in plant growth.
Schroth and Hancock classified microorganisms as plant growth-promoting rhizobacteria (PGPR) and deleterious rhizobacteria (DR). They pointed out that the greatest prospects for substantially increasing plant yields and making a dramatic change in agricultural practices may involve beneficial microorganisms that protect plant roots from the many deleterious microorganisms that occur in all agricultural soils.