Vesicular‐Arbuscular Mycorrhizal Fungus Infestation and Phosphorus Fertigation to Overcome Pepper Stunting after Methyl Bromide Fumigation1

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Abstract
Fumigation with methyl bromide (MB) is practiced to control pepper (Capsicum annuum L.) collapse disease, but in P‐sorbing soils the plants grow poorly after fumigation. A field trial was conducted on a high P‐sorbing soil (fossiliferous Typic Torriorthents) to compare P‐fertigation effects on plants grown on fumigated soil subsequently inoculated with Glomus macrocarpum Tul. & Tul. [MB plus vesicular‐arbuscular mycorrhizal fungus (MB+VAMF)] and not inoculated (MB), and on nonfumigated soil (NF). Pepper plants in MB+VAMF were most mycorrhizal, and MB plants the least. Both VAMF inoculation and P fertigation controlled early season stunting. Plants fertigated with 1.3 mmol P L−1 weighed the most 9 weeks after seeding, and among them the MB+VAMF plants were the heaviest. After 9 weeks, all plots were fertigated with 0.6 mmol P L−1. Yields were high (61 to 65 Mg ha−1) where 0.4 mmol P L−1 and more was supplied early in the season, and highest (73 to 74 Mg ha−1) where both P fertigation and VAMF inoculation were used. The presence of significant quantities of mycorrhiza early in the growth season induced the highest percentage of large‐size fruit, thus making P fertilization with VAMF inoculation most beneficial. Phosphorus fertilization recommendations may have to be adjusted when used in conjunction with soil treatments that significantly reduce VAMF populations in the soil. High sorption made it impossible to raise the P concentration in the soil solution to a level that would support maximum nonmycorrhizal‐pepper growth, unless large quantities of P were supplied frequently in the irrigation water.