Use of biological amendments in vegetable transplant production may affect plant development. Rhizosphere bacteria can alter conditions in the root zone and affect plant growth even if root tissue is not colonized. Arbuscular mycorrhizae (AM) affect plant development through symbiotic relations. Abiotic factors may mediate effects of biotic amendments. Organically certified potting medium was inoculated with a mix of Sinorhizobium sp. bacteria or a mix of AM fungi. Controls consisted of no amendment. Bell pepper, Capsicum annuum L., cv. Jupiter, seed were sown in the medium and irrigated either twice a day for 3 minutes per application or three times a day for 2 minutes per application. Seedlings were treated with 8, 16, 24, or 32 mL·L–1 of an organically certified liquid fertilizer beginning 3 weeks after sowing. Use of bacteria improved plant height and dry weight. Interactions of bacteria and fertilizer rate or irrigation regime affected plant height or dry weight. When irrigated twice a day, plants were tallest when provided 16 mL·L–1 fertilizer, and heaviest when provided 24 mL·L–1 fertilizer. When irrigated three times a day, plants were taller at the lower rates of fertilizer and heaviest at the highest rate of fertilizer. Use of AM had little effect on plant height and dry weight. Most of the responses when AM was the amendment were the result of fertilizer rate and irrigation regime. When irrigated twice a day, AM-treated plants were tallest and heaviest when provided at least 24 mL·L–1 fertilizer. Regardless of biological amendment, plant heights were correlated with plant dry weights over fertilizer rates and irrigation regime. Use of Sinorhizobium sp. appeared to provide a benefit to the development of bell pepper transplants.
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