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- Author or Editor: H.A.J. Hoitink x
A variety of publications from the United States (9, 10, 16, 22, 28), Norway (27), Belgium (4, 5, 6), Finland (18), and Japan (30) have discussed composting of tree barks for use in container media. Although differences in properties of bark from tree species are considerable, established methods for production of high quality composts are remarkably similar. The composting process comprises a complex series of biological events that remove mostly cellulose (wood and cambium) and various toxins (24, 29) from bark and leave humic acid, lignins and a variety of microorganisms as major end products. In this article, key factors are discussed that affect the composting rate of tree barks and quality of the end product. Information presented is based on research performed at the Ohio Agricultural Research and Development Center during the past 8 years as well as research at other institutions. Some guidelines were established in cooperation with various commercial operations that produce compost for container media.
Many factors affect the potential for composts to provide biological control of diseases caused by soilborne plant pathogens. Heat exposure during composting kills or inactivates pathogens and weed seeds if the process is monitored properly. Unfortunately, most beneficial microorganisms also are killed by this heat treatment. Conditions must be provided after peak heating that enhance natural recolonization of composts by biocontrol agents. The raw feedstock, the environment in which the compost is produced, as well as conditions during curing and utilization, determine the potential for recolonization by this microflora and the induction of disease suppression. Controlled inoculation of compost with biocontrol agents has proved necessary to induce consistent levels of suppression on a commercial scale. Compost stability is another important factor. Immature composts serve as food for pathogens and increase disease even when biocontrol agents are present. On the other hand, excessively stabilized organic amendments, such as highly decomposed peats, do not support the activity of biocontrol agents and disease therefore develops. Finally, salinity, C to N ratio, and other factors affect suppressiveness. Each of these factors will be discussed.
Rhizoctonia and Pythium crown and root rot of Euphorbia pulcherrima willd ex Kotzch cv. Annette Hegg Dark Red were suppressed in a composted hardwood bark medium amended with sphagnum peat. The suppression equalled that obtained in an aerated steam-treated peat medium drenched with fungicidies. Growth of ‘Annette Hegg Dark Red’ produced in the sphagnum peat-amended bark was improved over plants produced in a sterilized and fungicide drenched soil-peat-perlite medium. Addition of muck to composted hardwood bark negated the desirable growth effects.