Impact of Arbuscular Mycorrhizal Fungi on P Use Efficiency and Root Diseases of Onion Crops in the Columbia Basin: Progress Report

This progress report summarizes field research evaluating arbuscular mycorrhizal fungi (AMF) inoculants and phosphorus (P) fertilization in onion production systems. Trials were conducted to assess how AMF and P availability influence onion growth, yield, and nutrient uptake under field conditions. Treatments included combinations of mycorrhizal inoculation and varying phosphorus levels to determine whether AMF can enhance nutrient acquisition or reduce fertilizer needs. Measurements included plant growth, yield, and tissue nutrient concentrations. Results to date indicate variable responses to AMF inoculation, with outcomes dependent on soil conditions and phosphorus availability. In some cases, AMF did not significantly improve plant performance, suggesting that benefits may be context-specific and influenced by existing soil microbial communities or nutrient status. This work contributes to understanding when biological inputs such as mycorrhizal inoculants are effective in commercial vegetable systems and helps inform management strategies aimed at improving nutrient efficiency.