Mycorrhizal Infection and Growth of Onion in the Field in Relation to Phosphorus and Water Availability

Abstract

Vesicular-arbuscular (VA) mycorrhizal colonization of onion ( Allium cepa L.) roots was found at high levels in commercially used soils only when P concentrations were below 30 µg/cm 3 . Soils sampled were muck soils with varying amounts of organic matter and sand and marl soils, and the P range was 10-250 µg/cm 3 . Onions were also seeded in 2 fields of Houghton muck soil, at 4 P levels, with and without inoculum of Glomus etunicatus Becker & Gerdemann. High colonization occurred when soil P concentrations were below 15-20 µg/cm 3 . High yields and high colonization past midseason were achieved simultaneously upon the addition of 30 kg/ha P. In a separate experiment, onions were grown at 3 P levels and 2 watering regimes. The P concentrations associated with limited mycorrhizal root colonization shifted from 15 to 30 µg/cm 3 with a decrease in water availability. The results demonstrate the need for control of soil water conditions, as well as P, when attempting to utilize VA mycorrhizae.