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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #149274
Title: EVALUATION OF COMMERCIAL INORGANIC AND ORGANIC FERTILIZER EFFECTS ON ARBUSCULAR MYCORRHIZAE

Author
item Linderman, Robert
item Davis, Elizabeth

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2003
Publication Date: 3/1/2004
Citation: Linderman, R.G., Evaluation Of Commercial Inorganic And Organic Fertilizer Effects On Arbuscular Mycorrhizae. HortTechnology. 2004. v14(2) p. 196-202.

Interpretive Summary: Establishment of a symbiotic association between plant roots and mycorrhizal fungi is affected my many environmental and cultural conditions, among which fertilization is one of the most important. Growers need to know which fertilizers are the most compatible with the formation of mycorrhizae, so we compared different commercially available fertilizers, both inorganic and organic, to determine which group was generally more conducive to mycorrhiza formation, and which allowed the best mycorrhiza-induced growth response under P-limiting conditions. Experiments showed that generally organic fertilizers were more compatible with mycorrhiza formation than inorganic fertilizers, unless the P content of the latter was low. However, the lower N:P:K formulations of the organic fertilizers and the release of nutrients as a result of microbial degradation resulted in poorer overall plant growth of onions or miniature roses. Furthermore, organic fertilizers enhanced growth only if mycorrhizae were present, a result that could be attributed to several possible factors not addressed in this study. This research will provide growers with some guidelines to use in selecting fertilizers that would best allow for inoculation with mycorrhizal fungi and the realization of their benefits of improved water and nutrient use efficiency, tolerance of soil toxicities, improved transplantability, and greater disease resistance.

Technical Abstract: Summary: Arbuscular mycorrhizae (AM) are affected by fertility in soil or soilless container mixes. Several controlled-release inorganic (CRI) fertilizers were compared with several organic (OR) fertilizers at different rates (1/2-4X the recommended rate) to determine (1) threshold levels of tolerance by the AM fungus Glomus intraradices in relation to root colonization, and (2) growth responses of `Guardsman¿ bunching onion (Allium cepa) and `Orange Cupido¿miniature rose (Rosa sp.) plants, inoculated or not with AM. AM colonization in soil was decreased or totally inhibited by CRI fertilizers with high P at the 2-4X rates, whereas colonization was decreased but never eliminated by low-P OR fertilizers at the 34X rates. Shoot growth of onions was similar with or without AM inoculation when fertilized with CRI, but generally was only enhanced by OR fertilizers if inoculated with AM fungi, compared to the non¿AM controls. Shoot and root growth of onions were significantly increased by AM inoculation with OR fertilizers at 1X. In contrast, root growth was not increased with CRI fertilizers and AM fungal inoculation. Inoculation of miniature roses grown in sandy loam and fertilized with all the CRI or OR fertilizers resulted in high AM colonization, but without much AM-induced growth increase except where OR or CRI fertilizers with low P were used. In a soilless potting mix, growth of miniature roses was less with OR than CRI fertilizers, but mycorrhiza formation was greater in the former unless P was low in the latter. These results indicate that release of nutrients from organic fertilizers, as a result of microbial activity, favors AM establishment and function more than most inorganic fertilizers unless P levels of the latter are low.