The Effect of Soil Phosphorus Levels on Colonization of Onion Roots by Arbuscular Mycorrhizal Fungi, 2016–2017

Researchers conducted a controlled growth chamber study in 2016 to evaluate how formulation and application method influence the effectiveness of arbuscular mycorrhizal fungi (AMF) inoculants in onion seedlings. The experiment tested five treatments using the commercial AMF product Mykos Gold: a non-inoculated control, liquid formulation applied as a seed treatment, liquid formulation applied as a soil drench, granular formulation banded on soil, and granular formulation incorporated into soil. Onion seeds were planted in pasteurized soil collected from an organic field with relatively low phosphorus levels, and seedlings were grown under controlled temperature and light conditions. Researchers measured emergence, plant height, dry biomass, foliar nutrient concentrations, and AMF root colonization. The granular AMF treatments resulted in significant colonization of onion roots, averaging 34% when banded on soil and 39% when incorporated. In contrast, the liquid formulation did not result in detectable colonization. Despite increased colonization and some increases in foliar nitrogen and calcium, AMF treatments did not significantly affect seedling growth or biomass.