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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #140514
Title: VESICULAR-ARBUSCULAR MYCORRHIZA AND GROWTH RESPONSES OF SEVERAL ORNAMENTAL PLANTS GROWN IN SOILLESS PEAT-BASED MEDIUM AMENDED WITH COCONUT DUST (COIR)

Author
item Linderman, Robert
item DAVIS, E. - OREGON STATE UNIVERSITY

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2003
Publication Date: 7/1/2003
Citation: Linderman, R.G., Davis, E.A. 2003. Vesicular-arbuscular mycorrhiza and growth responses of several ornamental plants grown in soilless peat-based medium amended with coconut dust (coir). HortTechnology. 13(3):482-487.

Interpretive Summary: A recent material being used by the nursery industry as an amendment to potting mixes is coconut dust (coir). The literature indicates that the physical and chemical properties of coirs could be favorable to plant growth. However, no studies have been reported on its effect on beneficial microbes that might be added to potting mixes to enhance plant growth and health, such as mycorrhizal fungi. We evaluated the effects of different proportions of coir added to a peat-based medium on establishment of the VA mycorrhizal fungus, Glomus intraradices, and growth responses of several ornamental plants. We found that mycorrhiza formation was not affected significantly by coir amendment, but growth response of the several hosts was, probably due to changed nutrient-holding properties of the mixtures. These results indicate that mycorrhizae would not be adversely affected by coir amendment, but that chemical and even biological properties of the coir-peat mixtures could affect plant growth.

Technical Abstract: Coconut fiber dust (coir) is being used as a peat substitute or amendment to potting mixes because of its availability as well as its physical and chemical properties. Its effect on growth of different plants has been varied. Furthermore, its microbial composition and compatibility with beneficial microbes that might be added to growth media in the nursery, such as mycorrhizal fungi, has not been determined. In this study, coir was added as an amendment to a peat-based medium to determine growth effects on several ornamental plants heretofore not reported, and to determine its interaction with the VA mycorrhizal fungus Glomus intraradices. Mycorrhizae formed at least as well with coir amendment as with peat alone, and usually better. However, plant growth responses appeared to be independent of level of mycorrhizal colonization, and were plant species dependent. Consistent growth enhancement from mycorrhizae only occurred with marigold, and in one case (germander), growth was depressed with mycorrhizal inoculation at the 60% level of coir. Growth of lavender was depressed at all levels of coir compared to the unamended control. These results suggest that nutrient availability is changed in a peat-based potting medium by the addition of coir, but coir amendment generally has no deleterious effect on mycorrhiza formation. However, the magnitude of growth enhancement due to mycorrhizae was small for the plants tested in these media compared to that which occurs in a soil-based medium, presumably due to differences in nutrient P availability.